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Publication
- Yoo, S., and C.-H. Ho, 2024, Development of interpretable probability ellipse in tropical cyclone track forecasts using multiple operational ensemble prediction systems, Journal of Geophysical Research: Atmospheres, 129(4), e2023JD039295, https://doi.org/10.1029/2023JD039295
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- Ho, C.-H., D. Hyeon, M. Chang, G. McFarquhar, and S.-H. Won, 2024, Geostationary satellite-derived positioning of a tropical cyclone center using artificial intelligence algorithms over the western North Pacific, Bulletin of the American Meteorological Society, 105(3), E486-500, https://doi.org/10.1175/BAMS-D-23-0130.1
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- Chen, W., C.-H. Ho, S. Yang, Z. Wu, and H. Chen, 2024, Modulations of Madden-Julian oscillation and quasi-biweekly oscillation on early summer tropical cyclone genesis over Bay of Bengal and South China Sea, Journal of Climate, 37(6), 1951–1964, https://doi.org/10.1175/JCLI-D-23-0376.1
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- Kim, H.-A., J. Ho, G. Zhang, K. J. Ha, S.-Y. Hong, and C.-H. Ho, 2024, Polarimetric radar signatures in various lightning activities during Seoul (Korea) flood on August 8, 2022, Asia-Pacific Journal of Atmospheric Sciences, 2023, published online, https://doi.org/10.1007/s13143-023-00346-0
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- Park, D.-S. R., E. Seo, M. Lee, D.-H. Cha, D. Kim, C.-H. Ho, M.-I. Lee, H.-S. Kim, and S.-K. Min, 2024, Sea surface temperature warming to inhibit mitigation of tropical cyclone destructiveness over East Asia in El Niño, npj Climate and Atmospheric Science, 7, 24
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- Chang, M., C.-H. Ho, J. Ho, and E.-J. Cha, 2023, Centennial analysis in tropical cyclone induced precipitation in Korea, Weather and Climate Extremes, 39, 100549
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- Choi, W., C.-H. Ho, and K.-Y. Kim, 2023, Critical contribution of moisture to the air quality deterioration in a warm and humid weather, Scientific Reports, 13, 4260
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- Ho, C.-H., and K.-Y. Kim, 2023, Ineffective implementation of emergency reduction measures against high concentrations of particulate matter in Seoul, Repulic of Korea, Environmental Monitoring and Assessment, 195, 1127
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- Nam, C. C., D.-S. R. Park, and C.-H. Ho, 2023, Major decisive factors of tropical cyclone risk in the Republic of Korea: Intensity, track, and extratropical transition, Asia-Pacific Journal of Atmospheric Sciences, 59, 359-366
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- Ho, C.-H., I. Park, J. Kim, and J.-B. Lee, 2023, PM2.5 forecast in Korea using the long short-term memory (LSTM) model, Asia-Pacific Journal of Atmospheric Sciences, 59, 563-576
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- Moon, M., K.-J. Ha, D. Kim, C.-H. Ho, D.-S. R. Park, J.-E. Chu, S.-S. Lee, and J. C. L. Chan, 2023, Rainfall strength and area from landfalling tropical cyclones over the North Indian and western North Pacific oceans under increased CO₂ conditions, Weather and Climate Extremes, 41, 100581
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- Yun, J., S. Jeong, C.-H. Ho, N. Gruber, S. Piao, P. Ciais, D. Schimel, L. Gregor, and E. Y. Kwon, 2022, Enhanced seasonal amplitude of atmospheric CO2 by the Southern Ocean, Science Advances ,
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- Kripalani, R., K.-J. Ha, C.-H. Ho, J.-H. Oh, P. Bhaskar, M. Mujumdar, and A Prabhu, 2022, Erratic Asian summer monsoon 2020: Covid-19 lockdown initiatives possible cause for these episodes? , Climate Dynamics, https://doi.org/10.1007/s00382-021-06042-x
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- Kim, H.-S., D.-S. R. Park, C.-H. Ho, I.-J. Moon, and J.C.L. Chan, 2022, Latitudinal variation of the lifetime maximum intensity location of Atlantic tropical cyclones controlled by the Atlantic Multidecadal Oscillation, Geophysical Research Letters, 49, e2021GL097459
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- Park, C.-K., D.-S. R. Park, C.-H. Ho, J.-Y. Park, J. Kim, and S. Yang, 2022, Possible influence of ENSO Modoki and Arctic Oscillation on spatiotemporal variability of spring precipitation over the western North Pacific, Asia-Pacific Journal of Atmospheric Sciences, https://doi.org/10.1007/s13143-022-00277-2
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- Choi, W., C.-H. Ho, J.-W. Heo, K.-Y. Kim, S.-W. Kim, and J. Kim, 2022, Recent air quality deterioration on weekends in Seoul, South Korea: A focus on external contribution, Asia-Pacific Journal of Atmospheric Sciences, https://doi.org/10.1007/s13143-022-00287-0
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- Kim, D., C.-H. Ho, I. Park, J. Kim, L.-S. Chang, and M.-H. Choi, 2022, Untangling the contribution of input parameters to an artificial intelligence PM2.5 forecast model using the layer-wise relevance propagation method, Atmospheric Environment, 276, 119034
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- Kim, D., C.-H. Ho, M. Hiroyuki, and D.-S. R. Park, 2021, Assessing the influence of large-scale environmental conditions on rainfall structure of Atlantic tropical cyclones: An observational study, Journal of Climate, 34, 2093–2106
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- Bherwani, H., S. Kumar, K. Musugu, M. Nair, S. Gautam, A. Gupta, C.-H. Ho, A. Anshul, R. Kumar, 2021, Assessment and valuation of health impacts of fine particulate matter during COVID-19 lockdown: A comprehensive study of tropical and sub tropical countries, Environmental Science and Pollution Research, 28, 44522–44537. doi: 10.1007/s11356-021-13813-w.
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- Chang-Hoi Ho, Chang-Kyun Park, Jeongmin Yun, Eun-Ju Lee, Jinwon Kim, Hee-Dong Yoo, 2021, Asymmetric expansion of summer season on May and September in Korea, Asia-Pacific Journal of Atmospheric Sciences, https://doi.org/10.1007/s13143-020-00220-3
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- Ho, C.-H. I. Park, H.-R. Oh, H.-J. Gim, S.-K. Hur, J. Kim, and D.-R. Choi, 2021, Development of a PM2.5 prediction model using a recurrent neural network algorithm for the Seoul metropolitan area, Republic of Korea, Atmospheric Environment, 245, 118021
[abstract]
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The National Institute of Environmental Research, the Ministry of Environment, has been forecasting the concentrations of particulate matter (PM) with a diameter ≤ 2.5 μm (PM2.5) over Seoul, Republic of Korea, in terms of four PM2.5 concentration categories (low, moderate, high, and very high) since August 31, 2013. The current model, the Community Multiscale Air Quality (CMAQ) model, is run four times a day to forecast air quality for up to two days in 6-h intervals. In 2018, the hit ratio (i.e., accuracy) of the model was 60%, with an additional increase of 10% with the involvement of a forecaster. The CMAQ was improved in this study by incorporating a recurrent neural network (RNN) algorithm for the Seoul Metropolitan Area. Input datasets to the RNN model—PM values, meteorological parameters, and back-trajectory tracks obtained from both observations and model forecasts—were sorted according to time as the RNN algorithm learns time sequence series information, unlike typical neural network algorithms. To reflect the seasonality of the meteorological parameters that influence the PM2.5 concentrations in the region, one year was divided into 36 sets of three-month periods (i.e., there are three sets for July: May–June–July, June–July–August, and July–August–September). Several indices representing the accuracy of the forecast were calculated based on the RNN model results for 2018 after training the model for the previous three years (2015–2017). The accuracy of the RNN model is 74–81% for forecast lead times up to two days, about 20% higher than the CMAQ-only forecasts and ~10% higher than the combined CMAQ-forecaster forecast. The RNN model probabilities of detection for both high and very high PM2.5 events are comparable to those of the CMAQ model; however, the RNN model notably reduces the false alarm rate. Overall, the RNN model yields higher performance than the current forecast methods. Hence, this model can be adopted as an operational forecast model in Korea. |
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- Cheung, H. M., Ho, C.-H., Chang, M., Kim, D., Kim, J., & Choi, W., 2021, Development of a track-pattern-based medium-range tropical cyclone forecasting system for the western North Pacific, Weather and Forecasting, 36(4), 1505-1518.
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- Altman, J., M. Saurer, J. Dolezal, N. Maredova, J.-S. Song, C.-H. Ho, and K. Treydte, 2021, Large volcanic eruptions reduce landfalling tropical cyclone activity: Evidence from tree rings, Science of the Total Environment, 775, 145899
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- Chang, M., D.-S. R. Park and C.-H. Ho, 2021, Possible cause of seasonal inhomogeneity in interdecadal changes of tropical cyclone genesis frequency over the western North Pacific, Journal of Climate, 34(2), 635-642, doi: https://doi.org/10.1175/JCLI-D-20-0268.1.
[abstract]
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An abrupt decrease in annual tropical cyclone genesis frequency (TCGF), which is statistically significant
only from October to December (OND), has been noticed over the western North Pacific Ocean. However, the seasonal
inhomogeneity of interdecadal changes in TCGF betweenONDand the other seasons (from January to September) and the
associated mechanisms are not clearly documented. This study examines and compares the different interdecadal changes in
OND and in January–September from 1979 to 2018. According to our analysis, the TCGF decrease in OND (2.2) accounts
for 79% of the total decrease (2.8) in annual TCGF after 1998, whereas the TCGF in January to September remains
unchanged. The key differences in large-scale environment are found from the extension of equatorial easterly wind
anomalies and attendant anticyclone anomalies in the subtropics. Under similar sea surface temperature (SST) warming
pattern in the tropical Indo-Pacific region (i.e., the La Niña–like SST warming), tropical precipitation is significantly enhanced
over the area where its seasonal peak occurs: the tropical Indian Ocean in OND and the tropical western Pacific in
January–September. Thus, the equatorial easterly wind anomalies extend westward to 1108E in OND and to 1458E in
January–September. Different extension of easterly wind anomalies results in different expansion of attendant large-scale
anticyclone anomaly over the subtropical western Pacific, which dominates the entire main development region inONDbut
not in January–September. To summarize, the different extensions of easterly wind anomalies under similar La Niña–like
SST warming are responsible for the seasonal inhomogeneity of interdecadal changes in TCGF. |
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- Chang, L.-S., G. Lee, H. Im, D. Kim, S.-M. Park, W. J. Choi, Y. Lee, D.-W. Lee, D.-G. Kim, Y.-W. Kim, J. Kim, and C.-H. Ho, 2021, Quantifying the impact of synoptic weather systems on high PM2.5 episodes in the Seoul metropolitan area, Korea, Journal of Geophysical Research, 126, e2020JD034085
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- Ho, Chang-Hoi, Jin-Woo Heo, Minhee Chang, Woosuk Choi, Jinwon Kim, Sang-Woo Kim, Hye-Ryun Oh, 2021, Regulatory measures significantly reduced air-pollutant concentrations in Seoul, Korea, Atmospheric Pollution Research,
[abstract]
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The Government of the Republic of Korea has enforced strict regulations to improve air quality since the early 2000s. The regulations are mainly focused on reducing vehicle emissions in the Seoul metropolitan region by conforming to the European emissions standards, replacing diesel buses with compressed natural gas buses, incentives for installing diesel exhaust after-treatment systems and buying eco-friendly vehicles. There was a 20% reduction in 2010s compared to the 2000s in terms of the mean concentrations of particulate matter (PM) with mean aerodynamic diameters of ≤10 μm (PM10) and 2.5 μm (PM2.5) during cold seasons (October through following February) although the decrease may not be entirely attributable to the regulations. The influences of other external factors such as transboundary transport of air pollutants and regional meteorological conditions cannot be neglected.
This study analyzes the change in the diurnal variations—two maxima at around 11 and 22 local time (LT) and two minima at around 6 and 16 LT—of air pollutant concentrations that may be closely related to the regulatory action in reducing local vehicle emissions. A reduction of over 40% for the amplitude of two PM concentrations at 11 LT was revealed when values from the 2010s were compared to those from the 2000s. There was a similar reduction for other vehicle exhaust gases including nitrogen dioxide, carbon monoxide, and sulfur dioxide. Additional analysis of the long-term trend in mixed layer height and surface wind speed showed that the change in environmental conditions in the diurnal time scale was either negligible or unfavorable for conditions which reduce PM concentrations. This study suggests that the mean concentration estimation may underestimate the regulatory effects, but the approach based on the diurnal variation may be a more accurate indicator. |
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- Lee, G., Y. G. Lee, E. Jeong, and C.-H. Ho, 2021, Roles of meteorological factors in inter-regional variations of fine and coarse PM concentrations over the Republic of Korea, Atmospheric Environment, 264, 118706
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- Choi, W., C.-H. Ho, J. Jung, M. Chang, and K.-J. Ha, 2021, Synoptic conditions controlling the seasonal onset and days of heatwaves over Korea, Climate Dynamics, 57, 3045–3053
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- Sun-Kyong Hur, Chang-Hoi Ho, Jinwon Kim, Hye-Ryun Oh, Youn-Seo Koo, 2021, Systematic bias of WRF-CMAQ PM10 simulations for Seoul, Korea, Atmospheric Environment, 244, 117904
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- Park, C.-K., M. Chang, C.-H. Ho, K.-J. Ha, J. Kim, and B.-J. Sohn, 2021, Two types of diurnal variations in heavy rainfall during July over Korea, Advances in Atmospheric Sciences, 38, 2201–2211
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- Chang-Kyun Park, Doo-Sun R. Park, Chang-Hoi Ho, Tae-Won Park, Jinwon Kim, Sujong Jeong, Baek-Min Kim, 2020, A dipole mode of spring precipitation between southern China and Southeast Asia associated with the eastern and central Pacific types of ENSO, Journal of Climate, 33(23), 10097-10111
[abstract]
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Because spring precipitation in East Asia is critical for recharging water resources after dry winter, its spatiotemporal variations and related mechanisms needs in-depth research. This study analyzed a leading spatiotemporal variability of precipitation over East Asia for the boreal springs (March–May) in 1979−2017. We found that a dipole mode dominates the anomalous spring precipitation between southern China and Southeast Asia with significant interannual and decadal variations. The interannual dipole mode is attributable to the eastern Pacific (EP) type El Niño-Southern Oscillation (ENSO) while the decadal dipole mode is related to the decadal variation of the central Pacific (CP) type ENSO. In the El Niño phases of both time scales, the anticyclonic anomaly over the South China Sea and Philippines causes moisture convergence (divergence) over southern China (Southeast Asia), resulting in positive (negative) precipitation anomalies therein; the opposite occurs in the La Niña phases. The ensemble experiments using the Community Atmosphere Model version 5.1 confirmed that the tropical sea surface temperature (SST) in the EP and CP-type ENSO can be the major drivers of the interannual and decadal dipole modes, respectively. About half of 15 climate models participating in the Coupled Model Intercomparison Project phase 5 (CMIP5) showed that the El Niño phase of dipole mode will become dominant in the future. The individual models' future projections however considerably vary, implying that there is still large uncertainty. |
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- Lee, G., C.-H. Ho, L.-S. Chang, J. Kim, M.-K. Kim, S.-J. Kim, 2020, Dominance of large-scale atmospheric circulations in long-term variations of winter PM10 concentrations over East Asia, Atmospheric Research, 238, 104871, https://doi.org/10.1016/j.atmosres.2020.104871
[abstract]
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Concentrations of wintertime particulate matters of diameters below 10 μm (PM10) in South Korea and China have decreased since the 2000s largely owing to the emissions reduction policies of the two countries; however, this decreasing tendency has been notably weakened, or even been reversed, in recent years. This study examines the influence of large-scale atmospheric circulations on this PM10 change over East Asia for the winters (December–February) of the 2004/05–2015/16 period using an empirical orthogonal function (EOF) analysis. The first EOF mode, which accounts for 32.7% of the total variance, indicates decreases in PM10 concentrations until 2012 and thereafter increases in them particularly at most stations in eastern and northeastern China. Regression patterns of meteorological variables with respect to the first EOF time series indicate that the wintertime PM10 variations over East Asia are greatly influenced by the Ural blocking; the weakening of the Ural blocking after 2014 led to the weakening of cold air flows from the north and provided atmospheric conditions favorable for bad air quality events over East Asia. The second EOF mode, which accounts for 20.1% of the total variance, shows a similar spatial distribution as the linear trend of PM10 concentrations during the analysis period and would be related to the long-term changes in emissions. Our findings emphasize that the long-term variations in air quality over East Asia are affected primarily by the variations in large-scale atmospheric circulations with secondary contributions from the changes in emissions. |
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- Yun, J., S.-J. Jeong, C.-H. Ho, H. Park, J. Liu, H. Lee, S. Sitch, P. Friedlingstein, S. Lienert, D. Lombardozzi, V. Haverd, A. Jain, S. Zaehle, E. Kato, H. Tian, N. Vuichard, A. Wiltshire, N. Zeng, 2020, Enhanced regional terrestrial carbon uptake over Korea revealed by atmospheric CO2 measurements from 1999 to 2017, Global Change Biology, https://doi.org/10.1111/gcb.15061
[abstract]
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Understanding changes in terrestrial carbon balance is important to improve our knowledge of the regional carbon cycle and climate change. However, evaluating regional changes in the terrestrial carbon balance is challenging due to the lack of surface flux measurements. This study reveals that the terrestrial carbon uptake over the Republic of Korea has been enhanced from 1999 to 2017 by analyzing long‐term atmospheric CO2 concentration measurements at Anmyeondo Station (36.53°N, 126.32°E) located in the western coast. The influence of terrestrial carbon flux on atmospheric CO2 concentrations (ΔCO2) is estimated from the difference of CO2 concentrations that were influenced by the land sector (through easterly winds) and the Yellow Sea sector (through westerly winds). We find a significant trend in ΔCO2 of −4.75 ppmv decade‐1 (p < 0.05) during the vegetation growing season (May through October), suggesting that the regional terrestrial carbon uptake has increased relative to the surrounding ocean areas. Combined analysis with satellite measured normalized difference vegetation index and gross primary production shows that the enhanced carbon uptake is associated with significant nationwide increases in vegetation and its production. Process‐based terrestrial model and inverse model simulations estimate that regional terrestrial carbon uptake increases by up to 9.9 and 4.2 Tg C decade−1, accounting for 13.4 and 5.7% of annual domestic carbon emissions averaged for the study period, respectively. Atmospheric chemical transport model simulations indicate that the enhanced terrestrial carbon sink is the primary reason for the observed ΔCO2 trend rather than anthropogenic emissions and atmospheric circulation changes. Our results highlight the fact that atmospheric CO2 measurements could open up the possibility of detecting regional changes in the terrestrial carbon cycle even where anthropogenic emissions are not negligible. |
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- Oh, H.-R., C.-H. Ho, Y.-S. Koo, K.-G. Baek, H.-Y. Yun, S.-K. Hur, D.-R. Choi, J.-G. Jhun, and J.-S. Shim, 2020, Impact of Chinese air pollutants on a record-breaking PMs episode in South Korea for 11-15 January 2019, Atmospheric Environment, doi: https://doi.org/10.1016/j.atmosenv.2020.117262
[abstract]
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A record-breaking episode of highly concentrated particulate matter (PM) with diameters ≤ 2.5 μm (PM2.5) and ≤10 μm (PM10) occurred in South Korea during the period January 11–15, 2019: the hourly PM2.5 (PM10) in Seoul was 188 μg m−3 (262 μg m−3) on January 14. At the Baengnyeong and Socheongcho stations, located in the Yellow Sea between China and Korea, the hourly PM2.5 concentration reached up to 155 μg m−3 and 119.8 μg m−3, respectively, 16−19-h prior to this episode. This and the fact that the maximum PM10 concentration at Baengnyeong was 199 μg m−3 indicated a westerly transport of air pollutants. Satellite observations and 72-h back trajectory analysis clearly indicate that air pollutants from China flowed into Korea via the westerlies. According to contribution analysis using particulate matter source apportionment technology in the Comprehensive Air-quality Model with extension, air pollutants originating from northeastern China including Hebei and Shandong provinces were largely linked to the present record-breaking high concentration event in Seoul. This study will elucidate the mechanism of transboundary transport of air pollutants and help East Asian countries cooperate on air quality management. |
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- Gim, Hyeon-Ju, Chang-Hoi Ho, Sujong Jeong, Jinwon Kim, Song Feng, Michael J.Hayese, 2020, Improved mapping and change detection of the start of the crop growing season in the US Corn Belt from long-term AVHRR NDVI, Agricultural and Forest Meteorology,
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- Chang-Kyun Park, Chang-Hoi Ho, Doo-Sun R. Park, Tae-Won Park, Jinwon Kim, 2020, Interannual variations of spring drought-prone conditions over three subregions of East Asia and associated large-scale circulations, Theoretical and Applied Climatology, 142, 1117-1131
[abstract]
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For proactive prevention of water shortage problems, it is important to understand the spatiotemporal variabilities of droughts and their development mechanisms. This study identified an interannual variation of spring drought-prone condition in each region of East Asia (EA)—northern, mid, and southern EA—for the period 1979–2015 by using the standardized precipitation evapotranspiration index (SPEI) and a hierarchical clustering analysis. According to our analyses, spring drought-prone condition in the northern EA region mainly depends on local surface heating and precipitation deficit due to adiabatic compression by a high-pressure anomaly over the region during the preceding winter to spring. The high-pressure anomaly was driven by an upper-level wave train propagating from the Europe related to a positive phase of the Arctic Oscillation. For drought-prone conditions in the mid and the southern EA regions, the local precipitation deficit caused by the negative moisture advection/convergence therein acts as a primary factor. During the preceding winter, the negative moisture advection/convergence anomalies both in mid and southern EA regions were induced by anomalous low-level cyclonic circulations over the western North Pacific related to the La Niña. In spring, however, the moisture condition in the southern EA region was affected by persistent La Niña while that in the mid-EA region was by the negative phase of North Pacific Oscillation. This gap makes the main location of the negative moisture advection/convergence anomalies just slightly different, but considerably alter the region exposed to the drought-prone condition. |
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- Park, C.-K., C.-H. Ho, R. J. Park, J.-H. Woo, C. Lim, D.-S. R. Park, H. Park, M. J. Kim, Y. Kim, S.-C. Hong, J. Kim, 2020, Projections of future drought intensity associated with various local greenhouse gas emission scenarios in East Asia, Terrestrial, Atmospheric and Oceanic Sciences, 31(1), 9-19
[abstract]
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Efforts to reduce greenhouse gas emissions are ongoing in many East Asian countries; however, their influences on future drought remain unknown. We analyzed future changes in drought intensity over East Asia using the Representative Concentration Pathway (RCP) 8.5 and the new two limiting local greenhouse gas emission scenarios in East Asia: National Institute of Environmental Research (NIER)-H scenario for high emission and NIER-L scenario for low emission. The two scenarios were made by a fully coupled global climate model with prescribed gas boundaries of high and low greenhouse gas emissions from an atmospheric chemistry model reflecting the up-to-date environmental policies of South Korea, China, and Japan. The application of a clustering analysis to the calculated drought index time series identified four zonally distributed drought regions in the present-day period (1951 - 2016). Among these regions, higher latitude regions showed a more rapidly increasing trend in drought intensity than other regions for the present-day period. All future scenarios projected the continuation of this meridional intensification trend of drought until 2100; however, the intensification rates in the NIER-L were much smaller than those in the RCP8.5 and NIER-H scenarios. Our results suggest that reducing greenhouse gas emissions is critical for East Asian countries to alleviate the potential damages of future droughts. |
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- Cho, H., S.-Y. Jun, C.-H. Ho, and G. McFarquhar, 2020, Simulations of winter Arctic clouds and associated radiation fluxes using different cloud microphysics schemes in the Polar WRF: Comparisons with CloudSat, CALIPSO, and CERES, Journal of Geophysical Research: Atmospheres, https://doi.org/10.1029/2019JD031413
[abstract]
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Arctic cloud simulations of the polar-optimized version of the Weather Research and Forecasting (Polar WRF) model were compared with retrievals using the CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation measurements. For the period from December 1, 2015 to January 31, 2016, a series of 24- to 48-hour simulations initialized daily at 00 UTC were examined. In particular, two cloud microphysics schemes, the Morrison double moment and the WRF single-moment 6-class (WSM6), were tested. The modelled cloud top heights had a correlation coefficient (r) of 0.69-0.72 with those from satellite retrievals, and a mean bias of less than 400 m. For the mean ice water content profile and mixed-phase cloud occurrence, the Morrison scheme's clouds were in better agreement with satellite retrievals than the WSM6. However, the use of the Morrison scheme resulted in underestimates of outgoing longwave radiation by -11.7 W m-2 compared to satellite observations. The bias was reduced to -0.4 W m-2 with the WSM6 which produced a stronger precipitation rate (by 10%) resulting in a drier and less-cloudy atmosphere. This also leads to the 7 W m-2 mean difference in the surface downward longwave radiation (DLR) between the schemes, which is large enough to explain the spread of the Arctic DLR in the current climate models. However, as the temporal variation in DLR showed good agreement with ground observations (r: 0.68-0.92), it is concluded that the Polar WRF can be useful for studying cloud effects on the winter Arctic surface climate. |
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- Ha, K.-J., J.-H. Yeo, Y.-W. Seo, E.-S. Chung, J.Y. Moon, X. Feng, Y.W. Lee, C.-H. Ho, 2020, What caused the extraordinarily hot 2018 summer in Korea?
, Journal of the Meteorological Society of Japan, https://doi.org/10.2151/jmsj.2020-009
[abstract]
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In 2018, heatwaves (HWs), which are defined as period of abnormally hot weather with the daily maximum temperature (T_Max) exceeding its 95th percentile threshold for at least three consecutive days, were prevalent during June to August, and temperature records were broken in many countries over East Asia (EA) including China (CH), Japan (JP), and the Korean Peninsula (KP). In particular, extreme HWs through July to August lasted for the longest duration with 21.3 days with T_Max reaching 36.9°C. The highest T_Max, recorded since 1907, exceeded to 41°C in Hongcheon, located east of Seoul in the KP. Here, we examine the factors that influenced the 2018 HW, and how these relate to the 1994 HW, which was second longest HW recorded in the KP. The results show that abnormally strong and northwestward extended anticyclone features observed in July 2018 lasted as a persistent North Pacific anticyclone anomaly until August 2018 centered at the northern KP. These anticyclone features subsequently formed as a modon-like blocking with a cyclonic anomaly in the East China Sea. Meanwhile, in August 1994, the North Pacific High (NPH) extended to eastern EA, which broked the meridional dipole structure and HWs do not persist. The NPH, which persisted till August 2018, was accompanied by a sinking motion, suppression of precipitation, anomalous maximum temperature, weakening of the westerly jet stream, and increased insolation due to clear sky. We find that the prolonged and northwestward-shifted NPH including the KP drove the extraordinarily hot 2018 summer in Korea. In addition, low precipitation and massive evapotranspiration with the persistent insolation in July 2018 influenced the dry condition at the surface. We suggest that the predictions for the location and duration of the NPH associated with the HWs are required to reduce heat-related mortality and the impact on agriculture due to excessive evapotranspiration. |
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- Jeong, S.-J., H. Park, C.-H. Ho, and J. Kim, 2019, Impact of urbanization on spring and autumn vegetation phenology in the Seoul capital area, South Korea, International Journal of Biometeorology, 63, 627-637
[abstract]
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Urbanization exerts anthropogenic forcing that affects regional climate and ecosystems. With increasing levels of urbanization associated with urban population growth in the near future, understanding of the impact of urbanization on terrestrial ecosystems is important for predicting future environmental changes. This study evaluates the impact of urbanization on spring and autumn phenology by addressing the relationship between population density and phenology at nine stations in the Seoul Capital Area (SCA), South Korea during 1991–2010. We analyze the spring budburst dates for the six species (Prunus mume, Forsythia koreana, Rhododendron mucronulatum, Prunus yedoensis, Prunus persica, and Prunus pyrifolia) and the leaf coloring date for the two species (Ginkgo biloba and Acer palmatum). Regardless of species, the density of the urban population shows significant negative (positive) relationships with spring (autumn) phenology. In the SCA, urban population increases are related to earlier spring budburst up to 13 days and delayed leaf coloring up to 15 days. The most apparent spring budburst sensitivity is observed in Prunus mume, whereas the most dominant autumn leaf coloring sensitivity is observed in Acer palmatum. The relationship between population density and phenology is supported by the difference in nocturnal temperatures between stations which varies with the population density. Our results suggest that, in addition to global warming, future population growth should be considered in ecosystem assessments of human-induced environmental changes. |
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- Kim, D., C.-H. Ho, D.-S. R. Park, and J. Kim, 2019, Influence of vertical wind shear on wind- and rainfall areas of tropical cyclones making landfall over South Korea, PLOS One, 14, 1, https://doi.org/10.1371/journal.pone.0209885
[abstract]
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The wind- and rainfall areas of tropical cyclones (TCs) making landfall over South Korea were examined for the period 1998–2013 by using the Modern Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) and Tropical Rainfall Measuring Mission (TRMM) 3B42 data. Here, the wind- and rainfall areas were defined as the regions where wind speeds and precipitation rates exceed 14 m s-1 and 80 mm day-1 within 1000 km from the TC center, respectively. In general, TCs show significantly asymmetric wind and rainfall structures, with strong vertical wind shear appearing over South Korea during the landfall period. The rainfall area significantly increases with environmental vertical wind shear while the wind area is not sensitive to it. Composite analyses of the cases of strong and weak vertical wind shear confirm that the increase of rainfall area is related to the asymmetric convection (rising/sinking motion in the downshear-left/upshear-right side) induced by the vertical wind shear. This work highlights the importance of local atmospheric environment in determining the area primarily affected by strong winds or heavy rainfall during TC landfalls. |
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- Choi, W., C.-H. Ho, J. Kim, and J. C. L. Chan, 2019, Near-future tropical cyclone predictions in the western North Pacific: Fewer tropical storms but more typhoons, Climate Dynamics, 53, 1341-1356
[abstract]
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This study presents forecasts of near-future tropical cyclone (TC) activities over the western North Pacific (WNP) using a TC track-pattern-based prediction model in conjunction with long-term free-run simulations from the National Centers for Environmental Prediction Climate Forecast System. The prediction shows that the East Asian coastal area will be affected by fewer TC landfalls. However, the number of stronger TC landfalls may increase in the near future (2016–2030) compared to the present-day period (2002–2015). The potential candidates for modulating the near-future TC activity are three large-scale climate variability: El Niño–Southern Oscillation (ENSO), the North Pacific sea surface temperature (NPSST) variation, and basin-wide warming of the Pacific. More frequent El Niño episodes in the near future may contribute to the activation of TC formations in the far-eastern tropical ocean, which generates a favorable influence on TC intensification due to longer distances and development periods over the ocean. NPSST variations have contrasting effects, i.e., they have unfavorable effects on TC genesis due to weak vorticity, while creating favorable conditions for TC intensification by providing more humid environments in the subtropics. The impact of overall Pacific warming on the changes in TC activities is low compared to that of the other two factors. Our results physically demonstrate the contributions of three WNP sea surface temperature variability on near-future TC activity, emphasizing the critical roles of ENSO and NPSST rather than the near-term warming effect. |
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- Kim, J.-H., M.-K. Kim, C.-H. Ho, R. J. Park, M. J. Kim, J. Lim, S.-J. Kim, C.-K. Song, 2019, Possible link between Arctic Sea ice and January PM10 concentrations in South Korea, Atmosphere, 10, 619, https://doi.org/10.3390/atmos10100619
[abstract]
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In this study, we investigated the possible teleconnection between PM10 concentrations in South Korea and Arctic Sea ice concentrations at inter-annual time scales using observed PM10 data from South Korea, NCEP R2 data, and NOAA Sea Ice Concentration (SIC) data from 2001 to 2018. From the empirical orthogonal function (EOF) analysis, we found that the first mode (TC1) was a large-scale mode for PM10 in South Korea and explained about 27.4% of the total variability. Interestingly, the TC1 is more dominantly influenced by the horizontal ventilation effect than the vertical atmospheric stability effect. The pollution potential index (PPI), which is defined by the weighted average of the two ventilation effects, is highly correlated with the TC1 of PM10 at a correlation coefficient of 0.75, indicating that the PPI is a good measure for PM10 in South Korea at inter-annual time scales. Regression maps show that the decrease of SIC over the Barents Sea is significantly correlated with weakening of high pressure over the Ural mountain range region, the anomalous high pressure at 500 hPa over the Korean peninsula, and the weakening of the Siberian High and Aleutian low. Moreover, these patterns are similar to the correlation pattern with the PPI, suggesting that the variability of SIC over the Barents Sea may play an important role in modulating the variability of PM10 in South Korea through teleconnection from the Barents Sea to the Korean peninsula via Eurasia. |
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- Chang, M., C.-H. Ho, J. C. L. Chan, M.-S. Park, S.-W. Son, and J. Kim, 2019, The tropical transition in the western North Pacific: The case of tropical cyclone Peipah (2007), Journal of Geophysical Research: Atmospheres, 124, 5151-5165, https://doi.org/10.1029/2018JD029446
[abstract]
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This study examines the transition of an extratropical disturbance to a tropical cyclone (TC), Peipah (2007), in the western North Pacific (WNP), using reanalysis and geostationary satellite data. Instead of regular diurnal fluctuations of deep convection, the pre‐TC disturbance accompanies deep convection only for short durations every other day. When the pre‐TC vorticity is traced back to 7 days prior to its formation, the traced‐back vorticity indicates a strong potential vorticity (PV) trough in the subtropical upper troposphere that originated from the midlatitude lower stratosphere. The quasi‐geostrophic forcing and reduced static stability at the leading edge of the PV trough result in the formation of an extratropical disturbance. The vertical structure of the extratropical disturbance shows maximum vorticity in the upper troposphere and cold temperature anomaly within it throughout the entire troposphere. As the extratropical disturbance moved into the tropical WNP, deep convection associated with quasi‐geostrophic dynamics over the warm ocean initiated tropical transition of the extratropical disturbance to a TC through diabatic redistribution of PV in the tropospheric column as well as transition of the cold anomaly into a warm anomaly within the vortex. With additional contribution of barotropic energy conversion in the lower troposphere, the warm‐core low system finally developed into a TC‐strength vortex. These results indicate that PV troughs of the stratospheric origin over the subtropical Pacific Ocean can contribute to TC formations in the WNP. |
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- Park, D.-S. R., C.-H. Ho, D. Kim, N.-Y. Kang, Y. Han, and H.-R. Oh, 2019, Tropical Cyclone as a possible remote controller of air quality over the Republic of Korea through poleward propagating Rossby waves, Journal of Applied Meteorology and Climatology, 58, 2523–2530
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- Chen, A., C.-H. Ho, D. Chen, and C., 2019, Tropical cyclone rainfall in the Mekong River Basin for 1983–2016, Atmospheric Research, 226, 66-75, https://doi.org/10.1016/j.atmosres.2019.04.012
[abstract]
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As home to about 70 million people, the Mekong River Basin (MRB), located in Mainland Southeast Asia, is often influenced by tropical cyclones (TCs) landfalling. The TCs not only cause flood and storm hazards, but also play important roles in providing freshwater resource and welcomed sediment transports. Our study focuses on the climatology of TCs and associated rainfall (TCR) in the MRB for 1983–2016. Results show that: (i) the mean landfall occurrence of TCs is 6.2 yr−1, leading to 36.7 mm yr−1 of annual mean TCR (2.5% of the annual total precipitation), which mainly occur in monsoon-TC season (i.e., June–November); (ii) TCs highly concentrate on the lower eastern MRB, generating the largest TCR contribution of 12.4% to the annual total precipitation; (iii) the annual mean contribution of TCs induced extreme precipitation - R20mm and R50mm (days of heavy precipitation rate ≥20 mm day−1 and ≥50 mm day−1, respectively) - to that from annual total precipitation is large in the lower eastern MRB; (iv) over 60% of the basin area is influenced by TCR on average; and (v) a significant weakening trend of the TC frequency has been observed. The present findings lay a foundation for further in-depth research of the potential influence of the dynamic TCs and the associated rainfall in the MRB. |
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- Knutson, T., S. J. Camargo, J. C. L. Chan, K. Emanuel, C.-H. Ho, J. Kossin, M. Mohapatra, M. Satoh, M. Sugi, K. Walsh, L. Wu., 2019, Tropical cyclones and climate change assessment: Part I. Detection and attribution, Bulletin of the American Meteorological Society, https://doi.org/10.1175/BAMS-D-18-0189.1
[abstract]
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An assessment was made of whether detectable changes in tropical cyclone (TC) activity are identifiable in observations and whether any changes can be attributed to anthropogenic climate change. Overall, historical data suggest detectable TC activity changes in some regions associated with TC track changes, while data quality and quantity issues create greater challenges for analyses based on TC intensity and frequency. A number of specific published conclusions (case studies) about possible detectable anthropogenic influence on TCs were assessed using the conventional approach of preferentially avoiding type I errors (i.e., overstating anthropogenic influence or detection). We conclude there is at least low to medium confidence that the observed poleward migration of the latitude of maximum intensity in the western North Pacific is detectable, or highly unusual compared to expected natural variability. Opinion on the author team was divided on whether any observed TC changes demonstrate discernible anthropogenic influence, or whether any other observed changes represent detectable changes. The issue was then reframed by assessing evidence for detectable anthropogenic influence while seeking to reduce the chance of type II errors (i.e., missing or understating anthropogenic influence or detection). For this purpose, we used a much weaker “balance of evidence” criterion for assessment. This leads to a number of more speculative TC detection and/or attribution statements, which we recognize have substantial potential for being false alarms (i.e., overstating anthropogenic influence or detection) but which may be useful for risk assessment. Several examples of these alternative statements, derived using this approach, are presented in the report. |
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- Knutson, T., S. J. Camargo, J. C. L. Chan, K. Emanuel, C.-H. Ho, J. Kossin, M. Mohapatra, M. Satoh, M. Sugi, K. Walsh, L. Wu., 2019, Tropical cyclones and climate change assessment: Part II. Projected response to anthropogenic warming, Bulletin of the American Meteorological Society, https://doi.org/10.1175/BAMS-D-18-0194.1
[abstract]
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We assess model-projected changes in tropical cyclone activity for a 2°C anthropogenic warming. Medium-to-high confidence projections include increased tropical cyclone rainfall rates, intensity, and proportion of storms that reach Category 4-5 intensity globally.
Model projections of tropical cyclone (TC) activity response to anthropogenic warming in climate models are assessed. Observations, theory, and models, with increasing robustness, indicate rising global TC risk for some metrics -- that are projected to impact multiple regions.
A 2°C anthropogenic global warming is projected to impact TC activity as follows: i) The most confident TC-related projection is that sea level rise accompanying the warming will lead to higher storm inundation levels, assuming all other factors are unchanged. ii) For TC precipitation rates, there is at least medium-to-high confidence in an increase globally, with a median projected increase of 14%, or close to the rate of tropical water vapor increase with warming, at constant relative humidity. iii) For TC intensity, ten of 11 authors had at least medium-to-high confidence that the global average will increase. The median projected increase in lifetime maximum surface wind speeds is about 5% (range 1–10%) in available higher resolution studies. iv) For the global proportion (as opposed to frequency) of TCs that reach very intense (Category 4–5) levels, there is at least medium-to-high confidence in an increase, with a median projected change of +13%. Author opinion was more mixed and confidence levels lower for the following projections: v) a further poleward expansion of the latitude of maximum TC intensity in the western North Pacific; vi) a decrease of global TC frequency, as projected in most studies; vii) an increase in global very intense TC frequency (Category 4–5), seen most prominently in higher resolution models; and viii) a slowdown in TC translation speed. |
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- Heo, J.-W., C.-H. Ho, T.-W. Park, W. Choi, J.-H. Jeong, and J. Kim, 2018, Changes in cold surge occurrence over East Asia in the future: Role of thermal structure , Atmosphere, 9, 222; doi:10.3390/atmos9060222
[abstract]
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The occurrence of wintertime cold surges (CSs) over East Asia is largely controlled by the surface air temperature (SAT) distribution at high latitudes and thermal advection in the lower troposphere. The thermodynamic background state over northeastern Asia is associated with the strength of the East Asian winter monsoon and the variation of Arctic Oscillation. This study assesses the importance of the SAT structure with thermal advection in determining the frequency of CS occurrences over East Asia through the analysis of nine atmosphere–ocean coupled global climate models participating in the Coupled Model Intercomparison Project Phase 5. The historical simulations can reproduce the observed typical characteristics of CS development. On the basis of this model performance, ensemble-averaged future simulations under the representative concentration pathway 8.5 project a reduction in CS frequency by 1.1 yr−1 in the late 21st century (2065–2095) compared to the present-day period (1975–2005). The major reason for less frequent CSs in the future is the weakened cold advection, caused by notable SAT warming over the northern part of East Asia. These results suggest that changes in the meridional SAT structure and the associated changes in thermal advection would play a more substantial role than local warming in determining future changes in the frequency of CS occurrences over East Asia. |
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- Jeong, S. J., H. Park, C.-H. Ho,and J. Kim, 2018, Impact of urbanization on spring and autumn phenology of deciduous trees in the Seoul Capital Area, South Korea, International Journal of Biometeorology, DOI: 10.1007/s00484-018-1610-7
[abstract]
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Urbanization exerts anthropogenic forcing that affects regional climate and ecosystems. With increasing levels of urbanization associated with urban population growth in the near future, understanding of the impact of urbanization on terrestrial ecosystems is important for predicting future environmental changes. This study evaluates the impact of urbanization on spring and autumn phenology by addressing the relationship between population density and phenology at nine stations in the Seoul Capital Area (SCA), South Korea during 1991–2010. We analyze the spring budburst dates for the six species (Prunus mume, Forsythia koreana, Rhododendron mucronulatum, Prunus yedoensis, Prunus persica, and Prunus pyrifolia) and the leaf coloring date for the two species (Ginkgo biloba and Acer palmatum). Regardless of species, the density of the urban population shows significant negative (positive) relationships with spring (autumn) phenology. In the SCA, urban population increases are related to earlier spring budburst up to 13 days and delayed leaf coloring up to 15 days. The most apparent spring budburst sensitivity is observed in Prunus mume, whereas the most dominant autumn leaf coloring sensitivity is observed in Acer palmatum. The relationship between population density and phenology is supported by the difference in nocturnal temperatures between stations which varies with the population density. Our results suggest that, in addition to global warming, future population growth should be considered in ecosystem assessments of human-induced environmental changes. |
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- Yun, Jeongmin, Su‐Jong Jeong, Chang‐Hoi Ho, Chang‐Eui Park, Hoonyoung Park, Jinwon Kim, 2018, Influence of winter precipitation on spring phenology in boreal forests, Global Change Biology, 10.1111/gcb.14414
[abstract]
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Understanding the variations in spring vegetation phenology associated with preseason climate conditions can significantly improve our knowledge on ecosystem dynamics and biosphere‐atmosphere interactions. Recent studies have shown that wet winters can delay the start date of the vegetation growing season (SOS) in the high latitudes. However, associated underlying mechanisms remain unclear due to the lack of observation sites as well as complex interactions between various climate and ecosystem variables. In this study, the impact of winter precipitation on year‐to‐year variations of the SOS in boreal forests from 1982−2005 was investigated. Two experiments were performed using the Community Land Model version 4.5. In the control experiment, observed precipitation was used; in the sensitivity experiment, precipitation in the year 1982 was repeated throughout the period. The SOS in the control experiment shows high temporal correlations with the SOS estimated from the satellite‐retrieved leaf area index, indicating that the land model is capable of simulating realistic response of vegetation to interannual climate variability. The effects of winter precipitation on the SOS are examined by comparing the two model experiments for wet‐ and dry winters. After wet winters, the SOS was delayed by 2.7 days over 70.1% of the boreal forests than after dry winters; this accounts for 42.5% of the interannual variation in the SOS. The SOS delay is related to the decrease in the growing degree‐days (GDD) based on soil temperatures, suggesting that the effects of heat exposure on vegetation growth is strongly modulated by winter precipitation. The GDD decrease is related to both the increase in snowmelt heat flux and reduced absorption of solar radiation, which are proportional to the amount of winter precipitation and the ratio of short plants to tall trees, respectively. Our results provide a physical basis for the winter precipitation‐SOS relationship, suggesting that an increase in winter precipitation can alleviate strong advancing trends in spring vegetation growth in conjunction with global warming even for temperature‐limited ecosystems. |
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- Chang-Eui Park, Su-Jong Jeong, Manoj Joshi, Timothy J. Osborn, Chang-Hoi Ho, Shilong Piao, Deliang Chen, Junguo Liu, Hong Yang, Hoonyoung Park, Baek-Min Kim, and Song Feng, 2018, Keeping global warming within 1.5 °C constrains emergence of aridification, Nature Climate Change, doi:10.1038/s41558-017-0034-4
[abstract]
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Aridity—the ratio of atmospheric water supply (precipitation; P) to demand (potential evapotranspiration; PET)—is projected to decrease (that is, areas will become drier) as a consequence of anthropogenic climate change, exacerbating land degradation and desertification1,2,3,4,5,6. However, the timing of significant aridification relative to natural variability—defined here as the time of emergence for aridification (ToEA)—is unknown, despite its importance in designing and implementing mitigation policies7,8,9,10. Here we estimate ToEA from projections of 27 global climate models (GCMs) under representative concentration pathways (RCPs) RCP4.5 and RCP8.5, and in doing so, identify where emergence occurs before global mean warming reaches 1.5 °C and 2 °C above the pre-industrial level. On the basis of the ensemble median ToEA for each grid cell, aridification emerges over 32% (RCP4.5) and 24% (RCP8.5) of the total land surface before the ensemble median of global mean temperature change reaches 2 °C in each scenario. Moreover, ToEA is avoided in about two-thirds of the above regions if the maximum global warming level is limited to 1.5 °C. Early action for accomplishing the 1.5 °C temperature goal can therefore markedly reduce the likelihood that large regions will face substantial aridification and related impacts. |
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- Hye-Ryun Oh, Chang-Hoi Ho, Doo-Sun R. Park, Jinwon Kim, Chang-Keun Song, and Sun-Kyong Hur, 2018, Possible relationship of weakened Aleutian Low and air quality improvement in Seoul, South Korea, Journal of Applied Meteorology and Climatology, 57, 2363-2373, https://doi.org/10.1175/JAMC-D-17-0308.1
[abstract]
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Cold-season air quality in Seoul, South Korea, has been improved noticeably between 2001 and 2015 with a near-50% decrease in the mean concentration of particulate matter with aerodynamic diameters ≤10 μm (PM10). Like the change in mean concentration, the occurrence frequency and intensity of the extreme-high-PM10 episodes exceeding 100 μg m−3 has significantly decreased as well. In addition to the multilateral efforts of the South Korean government to reduce air pollutant emissions, this study proposes that large-scale circulation changes also could have contributed to the air quality improvements. Specifically, the recent weakening of the Aleutian low may have intensified the tropospheric westerlies around the Korean Peninsula, resulting in a shorter residence time of particulate matter over South Korea. Thus, despite constant governmental effort to reduce pollutant emissions, the improvement in air quality over South Korea may be delayed if the Aleutian low recovers its past strength in the future. This study emphasizes the importance of the meteorological field in determining the air quality over South Korea. |
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- Choi, Woosuk, Chang-Hoi Ho, Maeng-Ki Kim, Jinwon Kim, Hee-Dong Yoo, Jong-Ghap Jhun, and Jee-Hoon Jeong, 2018, Season-dependent warming characteristics observed at twelve stations in South Korea over the recent 100 years, International Journal of Climatology, in press
[abstract]
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A number of studies on the surface warming in the Korean Peninsula reported that there has been a notable increasing trend of surface air temperatures over the past several decades. Here, by analysing long‐term surface air temperature data at 12 stations in South Korea that have records longer than 60 years, the authors show that the warming of spring and autumn temperatures is characterized by quasi‐linear increases with time whereas the warming in winter and summer is characterized by one or two abrupt jumps. Change‐point analysis of the seasonal‐mean temperature time series shows that abrupt jumps in winter temperatures occurred in the late 1940s and late 1980s, while the jump in summer temperatures occurred in 1994 at most stations. The shape of the frequency distribution of the daily‐mean temperature anomalies at all stations shifts to the warmer side after the jumps for both winter and summer. This shift in turn results in the decrease of cold extremes in winter and the increase of warm extremes in summer at all stations. Our results indicate that recent temperature records in South Korea are characterized by the two different types of warming according to seasons. |
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- Lee, G., H.-R. Oh, C.-H. Ho, D.-S. R. Park, J. Kim, L.-S. Chang, J.-B. Lee, J. Choi, M. Sung, 2018, Slow decreasing tendency of fine particles compared to coarse particles associated with recent hot summers in Seoul, Korea, Aerosol and Air Quality Research, 18, 2185-2194, doi: 10.4209/aaqr.2017.10.0403
[abstract]
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In Seoul, South Korea, particulate matters (PMs) significantly decreased for the period 2005-2015 in concert with the implementation of air pollution reduction policies. This study reveals that PM with a diameter smaller than 2.5 μm (PM2.5) has a slower decreasing tendency than PM in the 2.5-10-μm range (PM2.5-10) during summer and that this discrepancy is attributable to the large increase in the summer surface air temperature for the analysis period (0.13°C year-1). During the daytime, especially in the afternoon when the hourly surface air temperature and its increasing rate are high, the difference between the decreasing rates of PM2.5 and PM2.5-10 is pronounced. The slower decrease in PM2.5 compared to PM2.5-10 likely results from the secondary PM2.5 formation being accelerated by the increase in the surface air temperature. Other atmospheric variables that can affect concentrations of PMs, such as insolation, relative humidity, precipitation, wind speed, and sea-level pressure, do not show a meaningful relationship with the discrepancy in the decreasing tendency between the two PMs. Our finding emphasizes the necessity of continuous monitoring and analysis of long-term variability in concentrations of PMs and related meteorological conditions, and the independent establishment of reduction policies for PM2.5 and PM2.5-10 to prepare for anthropogenic climate change and the subsequent air quality change. |
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- Park, H., S. J. Jeong, C. H. Ho, C. E. Park, and J. Kim, 2018, Slowdown of spring green-up advancements in boreal forests, Remote Sensing of Environment, DOI: 10.1016/j.rse.2018.08.012
[abstract]
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There is a consensus that the spring phenology of deciduous forests is advancing in response to global warming. Since the late 1990s, however, this tendency of spring phenology advancement has been weakened in over 60% of boreal forests, particularly in Siberia (−0.58 day yr⁻¹ for 1982–1997 vs. −0.17 day yr⁻¹ for 1982–2013) and northwestern North America (NWNA; −0.42 day yr⁻¹ for 1982–1997 vs. 0.07 day yr⁻¹ for 1982–2013). This study investigated the major factor in the weakening trends in the advancement of the start of the growing season (SOS) based on the satellite-observed normalized difference vegetation index (NDVI) in two regions by quantifying the effects of four climatic fields—winter duration (WD; the number of freezing days), pre-season temperature (PT; accumulated temperature from late winter to early spring), green-up temperature (GT; accumulated temperature around the green-up date), and pre-season precipitation (PR; accumulated precipitation before the green-up date)—on changes in the spring green-up trend. The GT explained the majority of the slowdown in the SOS trends in recent decades. In Siberia, the GT increases contributed to the advancement of the SOS during the 1980s and 1990s; however, the GT increase reduced to less than half of these periods resulting in a slowdown of the SOS advancing trend since the early 2000s. In NWNA, GT increases and WD shortening drove the SOS advancement until the late 1990s; however, both effects have been diminished to near zero to result in no further SOS advancements. This study demonstrates that the recent slowdown of the SOS advancing trends over Siberia and NWNA was largely attributed to the weakening of the warming trends, rather than the sensitivity changes of spring phenology to climate variables. This study suggests that the natural climate variability strongly affects the decadal variations in the boreal forest spring phenology.
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- Kim, D., C.-H. Ho, D.-S. R. Park, J. C. L. Chan, and Y. Jung, 2018, The relationship between tropical cyclone rainfall area and environmental conditions over the subtropical oceans, Journal of Climate, 31, 4605-4616, doi: 10.1175/jcli-d-17-0712.1.
[abstract]
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In this study, the variation of tropical cyclone (TC) rainfall area over the subtropical oceans is investigated using the Tropical Rainfall Measuring Mission precipitation data collected from 1998 to 2014, with a focus on its relationship with environmental conditions. In the subtropics, higher moving speed and larger vertical wind shear significantly contribute to an increase in TC rainfall area by making horizontal rainfall distribution more asymmetric, while sea surface temperature rarely affects the fluctuation of TC rainfall area. This relationship between TC rainfall area and environmental conditions in the subtropics is almost opposite to that in the tropics. It is suggested that, in the subtropics, unlike the tropics, dynamic environmental conditions are likely more crucial to varying TC rainfall area than thermodynamic environmental ones. |
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- Cheung, H. M., C.-H. Ho, J.-G. Jhun, D.-S. R. Park, and S. Yang, 2018, Tropical cyclone signals on rainfall distribution during strong vs. weak Changma/Baiu years, Climate Dynamics, https://doi.org/10.1007/s00382-017-4014-1.
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- Gim, Hyeon-Ju
Ho, Chang-Hoi
Kim, Jinwon
Lee, Eun Ju, 2018, Urbanization may reduce the risk of frost damage to spring flowers: A case study of two shrub species in South Korea, PLOS ONE, 10.1371/journal.pone.0191428
[abstract]
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Regional warming, owing to urbanization, leads to earlier spring phenological events and may expose plants to hard freeze damage. This study examined the influence of urbanization on the risk of frost damage to spring flowers in South Korea from 1973 to 2015. For the analysis period, we categorized 25 cities into two groups: those showing rapid population growth (rPG) ≥ 200,000, including 13 cities, and those showing no or decreased population growth (nPG), including 12 cities. We then investigated the time from the last frost dates (LFDs) in spring to the first flowering dates (FFDs) for each group. The rPG group experienced significant spring warming of 0.47°C per decade, resulting in earlier LFDs and FFDs. For this group, the advancement of LFD was more rapid than that of FFD, and the days between these two dates increased from 0.42 to 0.47 days per decade, implying a reduced risk of frost damage. Spring warming and the advancement of FFDs and LFDs were relatively small for the nPG group, and the LFDs were rather delayed. Consequently, the days between LFDs and FFDs were reduced from −1.05 to −1.67 days per decade, indicating an increased risk of frost damage. The contrasting changes in the frost-damage risk between the two city groups can be attributed to distinct urban warming at night, which makes the LFDs substantially earlier in the rPG group. Therefore, this study suggests that the warming associated with urbanization may lessen the risk of spring frost damage to plants in rapidly growing urban areas. |
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- Gim, Hyeon-Ju
Park, Seon Ki
Kang, Minseok
Thakuri, Bindu Malla
Kim, Joon
Ho, Chang-Hoi, 2017, An improved parameterization of the allocation of assimilated carbon to plant parts in vegetation dynamics for Noah-MP, Journal of Advances in Modeling Earth Systems, doi: 10.1002/2016MS000890
[abstract]
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In the land surface models predicting vegetation growth and decay, representation of the seasonality of land surface energy and mass fluxes largely depends on how to describe the vegetation dynamics. In this study, we developed a new parameterization scheme to characterize allocation of the assimilated carbon to plant parts, including leaves and fine roots. The amount of carbon allocation in this scheme depends on the climatological net primary production (NPP) of the plants. The newly developed scheme is implemented in the augmented Noah land surface model with multiple parameterization options (Noah-MP) along with other biophysical processes related to variations in photosynthetic capacity. The scheme and the augmented biophysical processes are evaluated against tower measurements of vegetation from four forest sites in various regions—two for the deciduous broadleaf and two for the needleleaf evergreen forest. Results from the augmented Noah-MP showed good agreement with the observations and demonstrated improvements in representing the seasonality of leaf area index (LAI), gross primary production (GPP), ecosystem respiration (ER), and latent heat flux. In particular, significant improvements are found in simulating amplitudes and phase shift timing in the LAI seasonal cycle, and the amount of GPP and ER in the growing season. Furthermore, the augmented Noah-MP performed reasonably well in simulating the spatial distributions of LAI, GPP, and NPP in East Asia, consistent with the satellite observations. |
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- Choi, Yong-Sang
Gim, Hyeon-Ju
Ho, Chang-Hoi
Jeong, Su-Jong
Park, Seon Ki
Hayes, Michael J., 2017, Climatic influence on corn sowing date in the Midwestern United States, International Journal of Climatology, DOI: 10.1002/joc.4799
[abstract]
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This study investigated the climatic influence on the corn sowing date in the Midwestern United States by comparing the survey data of corn cultivation with meteorological records in nine states for the last 36 years (1979–2014). The results show that the year-to-year changes in the sowing date were significantly affected by springtime air temperature and precipitation in the nine states, although large state-to-state differences were found in the degree of sowing date–meteorology relationship. We determined that the 36-year climatological warm period (CWP) with daily mean temperatures ≥10 °C plays an important role in the state-to-state differences. For the states with longer CWPs, the influence of air temperature (precipitation) was generally weaker (stronger). This observed counteractive relationship should be considered for crop modelling for more effective assessment of the impact of climate change on agriculture. |
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- Chang-Eui Park, Su-Jong Jeong, Chang-Hoi Ho, Hoonyoung Park, Shilong Piao, Jinwon Kim, and Song Feng, 2017, Dominance of climate warming effects on recent drying trends over wet monsoon regions, Atmospheric Chemistry and Physics, 17(17):1-18, DOI: 10.5194/acp-17-10467-2017
[abstract]
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Understanding changes in background dryness over land is key information for adapting to climate change because of its critical socioeconomic consequences. However, causes of continental dryness changes remain uncertain because various climate parameters control dryness. Here, we verify dominant climate variables determining dryness trends over continental eastern Asia, which is characterized by diverse hydroclimate regimes ranging from arid to humid, by quantifying the relative effects of changes in precipitation, solar radiation, wind speed, surface air temperature, and relative humidity on trends in the aridity index based on observed data from 189 weather stations for the period of 1961–2010. Before the early 1980s (1961–1983), change in precipitation is a primary condition for determining aridity trends. In the later period (1984–2010), the dominant climate parameter for aridity trends varies according to the hydroclimate regime. Drying trends in arid regions are mostly explained by reduced precipitation. In contrast, the increase in potential evapotranspiration due to increased atmospheric water-holding capacity, a secondary impact of warming, works to increase aridity over the humid monsoon region despite an enhanced water supply and relatively less warming. Our results show significant drying effects of warming over the humid monsoon region in recent decades; this also supports the drying trends over warm and water-sufficient regions in future climate. |
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- Chang, Minhee, Chang-Hoi Ho, Myung-Sook Park, Jinwon Kim, and Myoung-Hwan Ahn, 2017, Multiday evolution of convective bursts during western North Pacific tropical cyclone development and nondevelopment using geostationary satellite measurements, Journal of Geophysical Research: Atmospheres, 122, doi:10.1002/2016JD025535
[abstract]
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Tropical cyclones (TCs) develop through latent heating from a series of deep convection. To investigate the evolution of diurnal convective burst (CB) activities prior to TC formation, we analyzed 463 tropical disturbances that developed (80) or not developed (383) into TCs over the western North Pacific during the 2007-2009 period. Geostationary satellite data allowed defining deep convection where infrared (IR) brightness temperature is lower than that of water vapor (WV). Diurnal expansions from time series of IR minus WV < 0 areas near disturbance vortex centers for 5 days are defined as CB events. Combined analysis with the Modern Era Retrospective-Analysis shows that the multiday convective-environmental evolution for TC formation is entirely different from nonformation processes in terms of the occurrence of two consecutive diurnal CB events. Multiday CBs (mCB) are observed in 67.5% of the 80 TC formation cases and in 13.8% of the 383 nonformation cases. Intensities of the middle-to-low tropospheric relative vorticity of these two groups are comparable on 4 to 5 days prior to TC formation. However, vorticity intensification is weak for nondeveloping disturbances in environments of strong vertical wind shear; these disturbances eventually decay. The vorticity of developing disturbances continuously intensifies to TC strengths. The remaining 32.5%of the TC cases without mCB show weaker initial vorticity, but rapid intensification over 3 day periods before TC formation. The present results reveal that mCB is a common feature in pre-TC stages, and large-scale environments of weak vertical wind shear are critical for the formation of TC-strength circulations. |
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- Choi, Woosuk, Chang-Hoi Ho, Doo-Sun R. Park, Jinwon Kim, and J.C.L. Chan, 2017, Near-Future Prediction of Tropical Cyclone Activity Over the North Atlantic, Journal of Climate, 30, 8795-8809
[abstract]
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Prediction of tropical cyclone (TC) activity is essential to better prepare for and mitigate TC-induced disasters. Although many studies have attempted to predict TC activity on various time scales, very few have focused on near-future predictions. Here a decrease in seasonal TC activity over the North Atlantic (NA) for 2016–30 is shown using a track-pattern-based TC prediction model. The TC model is forced by long-term coupled simulations initialized using reanalysis data. Unfavorable conditions for TC development including strengthened vertical wind shear, enhanced low-level anticyclonic flow, and cooled sea surface temperature (SST) over the tropical NA are found in the simulations. Most of the environmental changes are attributable to cooling of the NA basinwide SST (NASST) and more frequent El Niño episodes in the near future. The consistent NASST warming trend in the projections from phase 5 of the Coupled Model Intercomparison Project (CMIP5) suggests that natural variability is more dominant than anthropogenic forcing over the NA in the near-future period. |
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- Chang-Kyun Park, Chang-Hoi Ho, Su-Jong Jeong, Eun Ju Lee, Jinwon Kim, 2017, Spatial and temporal changes in leaf coloring date of Acer palmatum and Ginkgo biloba in response to temperature increases in South Korea, PLOS ONE, https://doi.org/ 10.1371/journal.pone.0174390
[abstract]
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Understanding shifts in autumn phenology associated with climate changes is critical for preserving forest ecosystems. This study examines the changes in the leaf coloring date (LCD) of two temperate deciduous tree species, Acer palmatum (Acer) and Ginkgo biloba (Ginkgo), in response to surface air temperature (Ts) changes at 54 stations of South Korea for the period 1989–2007. The variations of Acer and Ginkgo in South Korea are very simi- lar: they show the same mean LCD of 295th day of the year and delays of about 0.45 days year-1 during the observation period. The delaying trend is closely correlated (correlation coefficient > 0.77) with increases in Ts in mid-autumn by 2.8 days ̊C-1. It is noted that the LCD delaying and temperature sensitivity (days ̊C-1) for both tree species show negligible dependences on latitudes and elevations. Given the significant LCD-Ts relation, we project LCD changes for 2016–35 and 2046–65 using a process-based model forced by tempera- ture from climate model simulation. The projections indicate that the mean LCD would be further delayed by 3.2 (3.7) days in 2016–35 (2046–65) due to mid-autumn Ts increases. This study suggests that the mid-autumn warming is largely responsible for the observed LCD changes in South Korea and will intensify the delaying trends in the future. |
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- Lee, G., H.-R. Oh, C.-H. Ho, J. Kim, C.-K. Song, L.-S. Chang, J.-B. Lee, S. Lee, 2016, Airborne Measurements of High Pollutant Concentration Events in the Free Troposphere over the West Coast of South Korea between 1997 and 2011, Aerosol and Air Quality Research, 16, 1118-1130, DOI: 10.4209/aaqr.2015.06.0407
[abstract]
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Aircrafts enable the direct measurement of chemical components in the free troposphere (FT). This study employed airborne measurements to examine the occurrences of high concentrations of SO2 and NOx in the FT over the coastal region west of the Seoul metropolitan area, South Korea. The data from a long-term (1997-2011) airborne measurement campaign were used to determine the meteorological conditions favorable for carrying these pollutants into the Seoul area. The back trajectory analyses of 21 instances of high FT pollutant concentration events showed ascending patterns from the major pollutant sources, mainly the industrial complexes in eastern China, in 9 instances and passing patterns in 12 instances. In the ascending instances, developing low-pressure systems over the source regions provide favorable conditions to uplift air pollutants from the surface into the FT. In the passing instances, an anomalous low-pressure system near the surface prevented airflows from descending into the boundary layer and upper-level anticyclonic systems helped to keep the ascending airflows in the FT. This study proposes the basic mechanisms for predicting air quality in the Seoul area, considering that air pollutants in the FT often entrain into the boundary layer to increase local concentrations. |
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- Choi, Woosuk, Chang-Hoi Ho, Jinwon Kim, Hyeong-Seog Kim, Song Feng, KiRyong Kang, 2016, A track-pattern-based seasonal prediction of tropical cyclone activity over the North Atlantic, Journal of Climate, 29, 481-494
[abstract]
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A seasonal prediction model of tropical cyclone (TC) activities for the period August–October over the North Atlantic (NA) has been developed on the basis of TC track patterns. Using the fuzzy c-means method, a total of 432 TCs in the period 1965–2012 are categorized into the following four groups: 1) TCs off the East Coast of the United States, 2) TCs over the Gulf of Mexico, 3) TCs that recurve into the open oceans of the central NA, and 4) TCs that move westward in the southern NA. The model is applied to predict the four TC groups separately in conjunction with global climate forecasts from the National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2). By adding the distributions of the four TC tracks with pre-calculated weighting factors, this seasonal TC forecast model provides the spatial distribution of TC activities over the entire NA basin. Multiple forecasts initialized in six consecutive months from February to July are generated at monthly intervals to examine the applicability of this model in operational TC forecasting. Cross-validations of individual forecasts show that the model can reasonably predict the observed TC frequencies over NA at the 99% confidence level. The model shows a stable spatial prediction skill, proving its advantage for forecasting regional TC activities several months in advance. In particular, the model can generate reliable information on regional TC counts in the near-coastal regions as well as in entire NA basin. |
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- Ho, Chang-Hoi, Woosuk Choi, Jinwon Kim, Maeng-Ki Kim, and Hee-Dong Yoo, 2016, Does El Niño-Southern Oscillation affect the precipitation in Korea on seasonal time scales?, Asia-Pacific Journal of Atmospheric Sciences, 52, 395-403
[abstract]
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A number of studies in the past two decades have attempted to find the relationship between the precipitation in Korea and the El Niño-Southern Oscillation (ENSO) on various time scales. Comprehensive analyses of station precipitation data in Korea for the 61-year period, 1954-2014, in this study show that the effects of ENSO on the seasonal precipitation in Korea are practically negligible. The correlation between summer precipitation and ENSO is insignificant regardless of the intensity, type (e.g., eastern-Pacific or central-Pacific), and stage (e.g., developing, mature, or decaying) of ENSO. Somewhat meaningful correlation between ENSO and precipitation in Korea occurs only in the ENSO-developing fall. Because summer rainfall accounts for over half of the annual total and fall is a dry season in Korea, the overall effects of ENSO on precipitation in Korea are practically nonexistent. |
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- Sun-Kyong Hur, Hye-Ryun Oh, Chang-Hoi Ho, Jinwon Kim, Chang-Keun Song, Lim-Seok Chang, Jae-Bum Lee, 2016, Evaluating the predictability of PM10 grades in Seoul, Korea using a neural network model based on synoptic patterns, Environmental Pollution, 218, 1324-1333
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- Doo-Sun R. Park, Chang-Hoi Ho, Jinwon Kim. KiRyong Kang, Chaehyeon C. Nam, 2016, Highlighting socioeconomic damages caused by weakened tropical cyclones in the Republic of Korea, Natural Hazards, 82, 1301-1315
[abstract]
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To alleviate enormous socioeconomic damages by tropical cyclones (TCs), the Korean Meteorological Administration (KMA) retains a special warning system for strong TCs (STCs, maximum wind speed of the best-track data > 17m/s), but not for relatively weak TCs (WTCs) which are not regarded as threatening as STCs; the warning system encompasses complex extreme phenomena such as gust, downpour, storm surge, and wind wave possbily arising from STCs. However, it is necessary to examine if WTCs can be actually as harmful as STCs with various extreme phenomena. Here, we compare the risks and intensities of WTCs with those of STCs for each province by analyzing the national damage reports and the near-surface wind and rainfall records from 60 weather stations in the Republic of Korea. According to our result, WTCs bring huge damages comparable to STCs in the northwestern Korea, the most populated and the richest area in the country, while WTCs cause much less destruction that STCs in the southeast. The large damages in the northwestern Korea can be explained by different mean landfall locations between WTCs and STCs; the storm centers of WTCs make landfall closer to the northwestern coastline than STCs'. Significant correlations between wind/rainfall can the damage amount by WTCs suggest that WTCs can also induce multiple extreme phenomena like STCs. Thus, the KMA needs to develop a special warning system for WTC like for STCs. |
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- Choi, Woosuk, Chang-Hoi Ho, Chun-Sil Jin, Jinwon Kim, Song Feng, Doo-Sun R. Park, and Jae-Kyung E. Schemm, 2016, Seasonal forecasting of intense tropical cyclones over the North Atlantic and the western North Pacific basins, Climate Dynamics, 47, 3063-3075
[abstract]
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Intense tropical cyclones (TCs) accompanying torrential rain and powerful wind gusts often cause substantial socio-economic losses in the regions around their landfall. This study analyzes intense TCs in the North Atlantic (NA) and the western North Pacific (WNP) basins during the period 1982-2013. Different intensity criteria are used to define intense TCs for these two basins, category 1 and above for NA and category 3 and above for WNP, because the number of TCs in the NA basin is much smaller than that in the WNP basin. Using a fuzzy clustering method, intense TC tracks in the NA and the WNP basins are classified into two and three representative patterns, respectively. On the basis of the clustering results, a track-pattern-based model is then developed for forecasting the seasonal activities of intense TCs in the two basins. Cross-validation of the model skill for 1982-2013 as well as verification of a forecast for the 2014 TC season suggest that our intense TC model is applicable to operational uses. |
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- Park,T.-W., C.-H. Ho, J.-H. Jeong, J.-W. Heo and Yi Deng, 2015, A new dynamical index for classification of cold surge types over East Asia, Climate dynamics,
[abstract]
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The cold surges over East Asia can be classified into wave-train type and blocking type according to their dynamic origins. In the present study, two dynamic indices are proposed to objectively identify cold surge types using potential temperature (θ) on the dynamic tropopause at 2-potential vorticity units (2-PVU) surface. The two indices are designed to represent primary characteristics of the two types of cold surge. The wave-train index (WI) is defined as a difference of anomalous θ on the 2-PVU surface between the western North Pacific and northeast China, which captures a southward (northward) intrusion of cold (warm) air mass related to the trough-ridge pattern. The blocking index (BI) is defined as a difference of anomalous θ between the subarctic region and northeast China, which indicates air mass overturning related to a reversal of the usual meridional θ gradient commonly observed in the occurrence of blocking type cold surge. Composite analyses based on the distribution of the WI and BI clearly demonstrate the dynamic evolutions of corresponding cold surge types. The wave-train cold surge is associated with a southeastward expansion of the Siberian High and northerly wind near surface, which is caused by growing baroclinic waves. During the blocking cold surge, a geopotential height dipole indicating the subarctic blocking and deepening of East Asian coastal trough induces a southward expansion of the Siberian High and northeasterly wind. Compared to the wave-train type, the blocking cold surge exhibits a longer duration and stronger intensity. In the new framework of these dynamic indices, we can detect a third type of cold surge when both the wave-train and the blocking occur together. In addition, we can exclude the events that do not have the essential features of the upper tropospheric disturbances or the subarctic anticyclonic circulation, which are responsible for cold surge occurrence, using the new indices. |
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- Kim, D., C.-S. Jin, C.-H. Ho, J. Kim, and J.-H. Kim, 2015, Climatological features of WRF-simulated tropical cyclones over the western North Pacific, Climate Dynamics, 44, 3223-3235, doi: 10.1007/s00382-014-2410-3.
[abstract]
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Tropical cyclones (TCs) over the western North Pacific (WNP) are simulated for the 29 TC seasons of July–October from 1982 to 2010 using the regional Weather Research and Forecasting (WRF) model nested within global WRF model simulations. Averaged over the entire 29-year period, the nested global–regional WRF has reasonably simulated the climatology of key TC features such as the location/frequency of genesis and tracks. The dynamical and thermal structures of the simulated TCs are weaker than observations owing to the coarse spatial resolution of the regional WRF (50 km × 50 km). TC frequencies are somewhat underestimated over the East China Sea but are substantially overestimated over the South China Sea and the Philippine Sea with neighboring oceans between 10°N and 15°N. Categorization of the simulated TCs into six clusters based on the observed TC clusters and the associated large-scale circulation show that the nested simulation depicts the observed TC characteristics well except for two clusters associated with TCs traveling from the Philippine Sea to the East China Sea. Errors in the simulated TC genesis and tracks are mostly related to these two clusters. In the simulation, the monsoon confluent zone over the Philippine Sea is too strong, and the mid-latitude jet stream expands farther south than that in the observations. Overall results from this study suggest that the nested global–regional WRF can be useful for studying the TC climatology over the WNP. |
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- Choi, Y.-S. and C.-H. Ho, 2015, Earth and environmental remote sensing community in South Korea: A review, Remote Sensing Applications: Society and Environment, 2, 66-76,
[abstract]
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This paper is a review of the satellite remote sensing community in South Korea, in the field of Earth and environmental sciences. The community has been invigorated by the Communication, Ocean, and Meteorological Satellite (COMS), the first Korean geostationary satellite project. Since its successful launch on July 26, 2010, about 300 organizations have officially received remotely sensed COMS data. This paper describes how satellite remote sensing has been used for decision-making in Korea, and the evolution of the associated education system. Despite the rapid development of remote sensing, Korea is facing shortcomings in the applicability of remote sensing to industry and society. The two future geostationary satellites planned by the Korean Government, GK (Geo-KOMPSAT)-2A and GK-2B, for monitoring climate and the environment in East Asia from 2018/2019 will alleviate these shortcomings. |
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- Doo-Sun R. Park, Chang-Hoi Ho, Chaehyeon C. Nam,Hyeong-Seog Kim, 2015, Evidence of reduced vulnerability against tropical cyclones in the Republic of Korea, Environmental Research Letters, 10/054003
[abstract]
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On average, three tropical cyclones (TCs) affect the Republic of Korea each year, causing extensive
damage. To alleviate the TC-induced disasters, the Korean government has invested nearly 4% of its
annual budget in recent decades in prevention efforts; however, the effectiveness of this costly
program has not been evaluated. This study determined whether any evidence shows a reduced
vulnerability to TCs in Korea over 1979–2010 by utilizing multi-linear regression. Homelessness,
casualties, and property losses were individually examined. These explained variables were normalized
into the socio-economic circumstances of 2005 before the regression to eliminate the effect of
changing exposure by dealing with population and wealth at provincial levels. Three potential
explanatory variables based on nationwide weather-station data were considered, including the
maximum wind, maximum rainfall, and number of affected stations over each TC’s damaging period.
In addition, the annual per capita income, showing a quasi-linear increasing tendency, was used as an
additional explanatory variable to examine how vulnerability is altered. The results revealed that each
empirical model of homelessness, casualties, and property losses can account for 47%, 57%, and 57%
of each variance, respectively, which is highest when considering all four explanatory variables.
Consistently negative coefficients of the per capita income terms for all damage types suggest that the
vulnerability to TCs has been significantly reduced. This finding appears to be partly the result of the
national prevention effort, although it also can be attributed to other unintended adaptation factors,
such as building codes, industrial structures, and land use. |
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- Kim, M. J., R. J. Park, C.-H. Ho, J.-H. Woo, K.-C. Choi, C.-K. Song, and J.-B. Lee, 2015, Future ozone and oxidants change under the RCP scenarios, Atmospheric Environment, 101, 103-115,
[abstract]
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We investigate ozone air quality changes in 2050 caused by global changes in climate and anthropogenic emissions of ozone precursors by using a global chemical transport model driven by meteorological fields from a general circulation model. We use projected emissions based on the Representative Concentration Pathway (RCP) scenarios and conduct model simulations to quantify the effects of climate and emission changes on future air quality, focusing on ozone in surface air. Our model results show that annual mean concentrations of surface ozone will be lower in 2050 relative to 2000 by −3.3, −3.7, and −4.2 ppbv under RCP6.0, RCP4.5, and RCP2.6, respectively. In contrast, the RCP8.5 projection results in a slight increase of 2.1 ppbv caused by a methane increase. The ozone reductions are driven primarily by decreases in NOx emission, which dominate the climate penalty on ozone driven by temperature increases. We also estimate the effect of 21st century climate change on ozone air quality, assuming no changes in anthropogenic emissions of ozone precursors in the future. We further use a statistical method to analyze the results in order to quantify the effect of each meteorological variable change on ozone concentration in summer. Temperature increase is found to result in ozone increases of up to 2.2 ppbv over land. Ozone over the oceans, however, is largely reduced with specific humidity increase, particularly in the Northern Hemisphere, where the ozone concentration decreases by 0.8 ppbv. We find that future increases in natural NOx emissions from lightning and soil make an important contribution to the formation of nitric acid and might seriously offset future decreases in nitrogen deposition caused by anthropogenic NOx emission reduction. |
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- Oh, H.-R. C.-H. Ho, J. Kim, D. Chen, S. Lee,
Y.-S. Choi, L.-S. Chang, C.-K. Song, 2015, Long-range transport of air pollutants originating in China: A possible
major cause of multi-day high-PM10 episodes during cold season in
Seoul, Korea, Atmospheric Environment, 109, 23-30
[abstract]
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Massive air pollutants originating in China and their trans-boundary transports are an international
concern in East Asia. Despite its importance, details in the trans-boundary transport of air pollutants over
East Asia and its impact on regional air quality remain to be clarified. This study presents an evidence
which strong support that aerosols emitting in China play a major role in the occurrence of multi-day (4
days) severe air pollution episodes in cold seasons (October through March) for 2001e2013 in Seoul,
Korea, where the concentration of PM10 (particulates with diameters 10 mm) exceeds 100 mg m3.
Observations show that these multi-day severe air pollution episodes occur when a strong high-pressure
system resides over the eastern ChinaeKorea region. In such weather conditions, air pollutants emitted
in eastern China/southwestern Manchuria are trapped within the atmospheric boundary layer, and
gradually spread into neighboring countries by weak lower tropospheric westerlies. Understanding of
trans-boundary transports of air pollutants will advance the predictability of local air quality, and will
encourage the development of international measures to improve air quality. |
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- Park, H., Jeong, S. J., Ho, C. H., Kim, J., Brown, M. E., & Schaepman, M. E. , 2015, Nonlinear response of vegetation green-up to local temperature variations in temperate and boreal forests in the Northern Hemisphere, Remote Sensing of Environment, 165, 100-108
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- Lee, J.-B., J.-S. Cha, S.-C. Hong, J.-Y. Choi, J.-S. Myoung, R. J. Park, J.-H. Woo, C.-H. Ho, J.-S. Han, and C.-K. Song, 2015, Projection of summertime ozone concentration over East Asia under multiple IPCC SRES emission scenarios, Atmospheric Environment, 106, 335-346,
[abstract]
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We have developed the Integrated Climate and Air Quality Modeling System (ICAMS) through the one-way nesting of global–regional models to examine the changes in the surface ozone concentrations over East Asia under future climate scenarios. Model simulations have been conducted for the present period of 1996–2005 to evaluate the performance of ICAMS. The simulated surface ozone concentrations reproduced the observed monthly mean concentrations at sites in East Asia with high R2 values (0.4–0.9), indicating a successful simulation to capture both spatial and temporal variability. We then performed several model simulations with the six IPCC SRES scenarios (A2, A1B, A1FI, A1T, B1, and B2) for the next three periods, 2016–2025 (the 2020s), 2046–2055 (the 2050s), and 2091–2100 (the 2090s). The model results show that the projected changes of the annual daily mean maximum eight-hour (DM8H) surface ozone concentrations in summertime for East Asia are in the range of 2–8 ppb, −3 to 8 ppb, and −7 to 9 ppb for the 2020s, the 2050s, and the 2090s, respectively, and are primarily determined based on the emission changes of NOx and NMVOC. The maximum increases in the annual DM8H surface ozone and high-ozone events occur in the 2020s for all scenarios except for A2, implying that the air quality over East Asia is likely to get worse in the near future period (the 2020s) than in the far future periods (the 2050s and the 2090s). The changes in the future environment based on IPCC SRES scenarios would also influence the change in the occurrences of high-concentrations events more greatly than that of the annual DM8H surface ozone concentrations. Sensitivity simulations show that the emissions increase is the key factor in determining future regional surface ozone concentrations in the case of a developing country, China, whereas a developed country, Japan would be influenced more greatly by effects of the regional climate change than the increase in emissions. |
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- Lee, Y. G., C.-H. Ho, J.-H. Kim, and J. Kim, 2015, Quiescence of Asian dust events in South Korea and Japan during 2012 spring: Dust outbreaks and transports, Atmospheric Environment, 114, 92-101,
[abstract]
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This study examined the quiescence of Asian dust events in South Korea and Japan during the spring of 2012, presenting a synoptic characterization and suggesting possible causes. Synoptic observation reports from the two countries confirmed that spring 2012 had the lowest number of dust events in 2000–2012. The monthly dust frequency (DF) in March 2012 over the dust source regions, i.e., deserts in northern China and Mongolia, indicated a significant decrease compared to the 12 year (2000–2011) March climatology. The DF in April 2012 was comparable to the 12 year climatology values, but in May 2012 it was slightly lower. The daily Ozone Monitoring Instrument Aerosol Index and the Navy Aerosol Analysis and Prediction System simulations revealed stagnant dust movement in March and May 2012. Anomalous anticyclones north of the source regions decreased the dust outbreaks and enhanced the southeasterly winds, resulting in few dust events over the downwind countries (i.e., South Korea and Japan). By contrast, in April 2012, a strong anomalous cyclone east of Lake Baikal slightly increased the dust outbreaks over northeastern China. However, the major dust outbreaks were not transported downwind because of exceptional dust pathways, i.e., the southeastward pathway of dust transport was unusually blocked by the expansion of an anomalous anticyclonic circulation over the Sea of Okhotsk, with dust being transported northeast. |
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- Park, C.-E., S.-J. Jeong, C.-H. Ho, J. Kim, 2015, Regional variations in potential plant habitat changes in response to multiple global warming scenarios, Journal of Climate, In Press, doi:10.1175/JCLI-D-13-00753.1
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- Park, M.-S., C.-H. Ho, H. Cho, and Y.-S. Choi, 2015, Retrieval of Outgoing Longwave Radiation from COMS Narrowband Infrared Imagery, Advances in Atmospheric Sciences, 32(3),375-388. doi: 10.1007/s00376-014-4013-7.
[abstract]
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Hourly outgoing longwave radiation (OLR) from the geostationary satellite Communication Oceanography Meteorological Satellite (COMS) has been retrieved since June 2010. The COMS OLR retrieval algorithms are based on regression analyses of radiative transfer simulations for spectral functions of COMS infrared channels. This study documents the accuracies of OLRs for future climate applications by making an intercomparison of four OLRs from one single-channel algorithm (OLR12.0 using the 12.0 μm channel) and three multiple-channel algorithms (OLR10.8+12.0 using the 10.8 and 12.0 μm channels; OLR6.7+10.8 using the 6.7 and 10.8 μm channels; and OLRAll using the 6.7, 10.8, and 12.0 μm channels). The COMS OLRs from these algorithms were validated with direct measurements of OLR from a broadband radiometer of the Clouds and Earth’s Radiant Energy System (CERES) over the full COMS field of view [roughly (50°S–50°N, 70°–170°E)] during April 2011.
Validation results show that the root-mean-square errors of COMS OLRs are 5–7 W m−2, which indicates good agreement with CERES OLR over the vast domain. OLR6.7+10.8 and OLRAll have much smaller errors (~6 W m−2) than OLR12.0 and OLR10.8+12.0 (~8 W m−2). Moreover, the small errors of OLR6.7+10.8 and OLRAll are systematic and can be readily reduced through additional mean bias correction and/or radiance calibration. These results indicate a noteworthy role of the 6.7 μm water vapor absorption channel in improving the accuracy of the OLRs. The dependence of the accuracy of COMS OLRs on various surface, atmospheric, and observational conditions is also discussed. |
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- Lee, Y. G., J. Kim, C.-H. Ho, S.-I. An, H.-K. Cho, R. Mao, B. Tian, D. Wu, J. N. Lee, O. Kalashnikova, Y. Choi, and S.-W. Yeh, 2015, The effects of ENSO under negative AO phase on spring dust activity over northern China: An observational investigation, International Journal of Climatology, 35, 935-947,
[abstract]
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The effects of El Niño/Southern Oscillation (ENSO) under negative Arctic Oscillation (AO) phase on the Asian dust activity are investigated for springs of the period 1961–2002. The spring dust index (DI) describing the monthly frequencies of three types of dust events (e.g. dust storm, blowing dust, and floating dust) exhibits a significant increase in the years of negative AO phase (hereafter AO−) and El Niño, compared with that in the years of AO− and La Niña. Averaged over all observation stations, the spring DI (49.7) during the El Niño/AO− years is higher by 11.4% or 29.8% than that (38.3) during the La Niña/AO− years. We suggest possible physical mechanism that the anomalous large-scale environments associated with AO− and El Niño are more effective to provide favourable conditions to enhance Asian dust activity. During the El Niño/AO− years, meridional gradients of pressure and temperature over the dust source regions are significantly enhanced by decreasing the geopotential height and warming air temperature that originated from the north and south of source regions, respectively, under the influence of AO− and El Niño. These also intensify the zonal wind shear and atmospheric baroclinicity, thereby producing enhanced cyclogenesis and dust occurrences over the major source regions. At the same time, dust transport paths with the stronger westerly winds are developed by the combined constraints of anomalous cyclone over the Siberia and the Mongolia and anomalous anticyclone over the western North Pacific, and thus strengthen dust transport to the downwind regions. |
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- Park, M.-S., H.-S. Kim, C.-H. Ho, R. L. Elsberry, M.-I. Lee, 2015, Tropical Cyclone Mekkhala's (2008) Formation over the South China Sea: Mesoscale, Synoptic-scale and Large-scale Contributions, Monthly Weather Review, 143(1), 88-110 . doi:10.1175/MWR-D-14-00119.1
[abstract]
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Tropical cyclone formation close to the coastline of the Asian continent presents a significant threat to heavily populated coastal countries. A case study of Tropical Storm Mekkhala (2008) that developed off the coast of Vietnam is presented using the high-resolution analyses of the European Center for Medium-range Weather Forecasts/Year of Tropical Convection and multiple satellite observations. We have analyzed contributions to the formation from large-scale intraseasonal variability, synoptic perturbations, and Mesoscale Convective Systems (MCSs). Within a large-scale westerly wind burst (WWB) associated with the Madden Julian Oscillation (MJO), synoptic perturbations generated by two preceding tropical cyclones initiated the pre-Mekkhala low-level vortex over the Philippine Sea. Typhoon Hagupit produced a synoptic-scale wave train that contributed to the development of Jangmi, but likely suppressed the Mekkhala formation. The low-level vortex of the pre-Mekkhala disturbance was then initiated in a confluent zone between northeasterlies in advance of Typhoon Jangmi and the WWB.
A key contribution to the development of Mekkhala was from diurnally-varying MCSs that were invigorated in the WWB. The oceanic MCSs, which typically develop off the west coast of the Philippines in the morning and dissipate in the afternoon, were prolonged beyond the regular diurnal cycle. A combination with the MCSs developing downstream of the Philippines led to the critical structure change of the oceanic convective cluster, which implies the critical role of mesoscale processes. Therefore, the diurnally-varying mesoscale convective processes over both the ocean and land are concluded to have an essential role in the formation of Mekkhala in conjunction with large-scale MJO and the synoptic-scale TC influences.
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- Park, T.-W., C.-H. Ho, and Y. Deng, 2014, A synoptic and dynamical characterization of wave-train and blocking cold surge over East Asia, Climate Dynamics, 43, 753–770, doi: 10.1007/s00382-013-1817-6
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- Choi, Y.-S., B.-M. Kim, S.-K. Hur, S.-J. Kim, J.-H. Kim, and C.-H. Ho, 2014, Connecting early summer cloud-controlled sunlight and late summer sea ice in the Arctic, Journal of Geophysical Research, 119, 11,087–11,099, doi:10.1002/2014JD022013.
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- Jeong, S.-J., C.-H. Ho, S. Piao, J. Kim, P. Ciais, Y.-H. Lee, J.-G. Jhun, and S. K. Park, 2014, Effects of double cropping on summer climate of the North China Plain and neighbouring regions, Nature Climate Change, 4, 615-619
[abstract]
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The North China Plain (NCP) is one of the most important agricultural regions in Asia and produces up to 50% of the cereal consumed in China each year1, 2. To meet increasing food demands without expanding croplands, annual agricultural practice in much of the NCP has changed from single to double cropping3, 4. The impact of double cropping on the regional climate, through biophysical feedbacks caused by changes in land surface conditions, remains largely unknown. Here we show that observed surface air temperatures during the inter-cropping season (June and July) are 0.40 °C higher over double cropping regions (DCRs) than over single cropping regions (SCRs), with increases in the daily maximum temperature as large as 1.02 °C. Using regional climate modelling, we attribute the higher temperatures in DCRs to reduced evapotranspiration during the inter-cropping period. The higher surface temperatures in June and July affect low-level circulation and, in turn, rainfall associated with the East Asian monsoon over the NCP and neighbouring countries. These findings suggest that double cropping in the NCP can amplify the magnitude of summertime climate changes over East Asia. |
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- Park, D.-S. R., C.-H. Ho, and J.-H. Kim, 2014, Growing threat of intense tropical cyclones to East Asia during the period 1977–2010, Environmental Research Letters, 9, 014008, doi:10.1088/1748-9326/9/1/014008
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- Choi, Y.-S., C.-H. Ho, C.-E. Park, T. Storelvmo, and I. Tan, 2014, Influence of cloud phase composition on climate feedbacks, Journal of Geophysical Research, 119, 3687-3700, DOI: 10.1002/2013JD020582
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- Choi, Y.-S., H. Cho, C.-H. Ho, R. S. Lindzen, S. K. Park, and X. Yu, 2014, Influence of non-feedback variations of radiation on the determination of climate feedback, Theoretical and Applied Climatology, 115(1-2), 355-364. doi:10.1007/s00704-013-0998-6
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- Feng, S., Q. Hu, W. Huang, C.-H. Ho, R. Li, and Z. Tang, 2014, Projected climate regimes shift under future global warming from 4 multi-model, multi-scenarios CMIP5 simulations, Global and Planetary Change, 112, 41–52
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- Jun, S.-Y., C.-H. Ho, B.-M. Kim, and J.-H. Jeong, 2014, Sensitivity of Arctic warming to sea surface temperature distribution over sea-ice melted region in AGCM experiments, Climate Dynamics, 42, 941-955, doi: 10.1007/s00382-013-1897-3
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- Lee, Y. G., J. Kim, C.-H. Ho, S.-I. An, H.-K. Cho, R. Mao, B. Tian, D. Wu, J. N. Lee, O. Kalashnikova, Y. Choi, S.-W. Yeh, 2014, The effects of ENSO under negative AO phase on spring dust activity over northern China: An observational investigation, International Journal of Climatology (accepted),
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- Kwon, M., S.-W. Yeh, Y.-G. Park, and Y.-K. Lee, 2013, Changes in the linear relationship of ENSO-PDO under the global warming, INTERNATIONAL JOURNAL OF CLIMATOLOGY, 33(5), 1121–1128.
[abstract]
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We examine changes in El Niño and Southern Oscillation (ENSO)/Pacific Decadal Oscillation(PDO) relationship under the global warming using coupled climate models participated in the Intergovernmental Panel on Climate Change(IPCC) Fourth Assessment Report(AR4). The temporal structure for the ENSO–PDO relationship is changed remarkably. The relationship between ENSO and PDO during the boreal winter (December, January and February) becomes stronger so that there would be more frequent in phase occurrence of ENSO and PDO (i.e. El Niño–a positive phase of PDO or La Niña–a negative phase of PDO). As PDO could constructively interfere with the ENSO-related climate when ENSO and PDO are in phase, in the future one may expect stronger climate signal because of ENSO in the mid latitude. The IPCC AR4 model also shows that the Pacific North America-like pattern is slightly shifted eastward and much stronger. We also discuss the possible reason for these changes |
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- Oh, H.-R., C.-H. Ho, and Y.-S. Choi, 2013, Comments on “Direct radiative forcing of anthropogenic aerosols over oceans from satellite observation”, Advances in Atmospheric Science, 30(1), 10-14, doi: 10.1007/s00376-012-1218-5
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- Jin, C.-S., C.-H. Ho, J.-H. Kim, D.-K. Lee, D.-H. Cha, S.-W. Yeh, 2013, Critical role of northern off-equatorial sea surface temperature forcing associated with central Pacific El Niño in more frequent tropical cyclone movements toward East Asia, Journal of Climate, 26, 2534–2545.
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- Oh, H. R., Choi, Y. S., Ho, C. H. and M. J. Jeong, 2013, Estimation of aerosol direct radiative effects for all-sky conditions from CERES and MODIS observations, Journal of Atmospheric and Solar-Terrestrial Physics, 102 : 311-320
[abstract]
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Satellite observations have shown the global average of the aerosol direct radiative effect (DRE) at the top of the atmosphere to be approximately −5.0 W m−2. Although there is a general consensus on this quantity, it is essentially biased toward clear-sky conditions. To circumvent this limitation, the present study introduces a new method for retrieving the global DRE of aerosol over the region of 60°S–60°N for all-sky conditions (both clear and cloudy skies). The all-sky DRE was calculated on a monthly basis by combining the measured DRE for a clear sky and the simulated DRE for a cloudy sky in 1°×1° grids. For the measured clear-sky DRE, we employed aerosol, cloud, and radiation fluxes from the Cloud and Earth's Radiant Energy System (CERES) instrument and the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra satellite for May 2000–December 2005. For the simulated cloudy-sky DRE, we performed radiative transfer modeling with the MODIS cloud properties in addition to the aerosol optical properties independently estimated in this study that include asymmetry factor and single scattering albedo. The results show that the global mean±standard deviation of DRE for the all-sky scene is −3.1±1.0 W m−2, which is weaker than that for the clear-sky only. This is in good agreement with the global estimates from previous studies based on different methods. The main advantage of our method is near-real-time estimation of monthly global all-sky DRE that has physical consistency with the CERES data. |
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- Lee, S., C.-H. Ho, Y. G. Lee, H.-J. Choi, C.-K. Song, 2013, Influence of transboundary air pollutants from China on the high-PM10 episode in Seoul, Korea for the period October 16-20, 2008, Atmospheric Environment,
[abstract]
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This study examines the extraordinarily long-lasting episode of high concentrations of particulate matter with diameter <10 mm (PM10) in Seoul, Korea over the period October 16e20, 2008. The concentration of PM10 increased up to 197.2 mg m3 and continually stayed above the daily environmental control standard value (100 mg/㎥) for the period. Satellite retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS), Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) showed pronounced transport of aerosols from China to the Korean peninsula prior to the high-PM10 episode. The updraft of air pollutants from the source region in China, transport by westerlies, and
subsequent descent to Seoul metropolitan regions are examined in the context of horizontal and vertical airflows. The connection between PM10 concentration over the Chinese source region and the Seoul target area is verified by wind back trajectory analysis. The meteorological conditions favorable for maintenance of the high PM10 levels are investigated through the analysis of weather maps and low-level stability. In this high-PM10 episode, the stagnant high-pressure system over Korea may play a decisive role in the descent and accumulation of air pollutants. The influence of transboundary air pollutants from China on the air quality in Korea and relevant meteorological environment found in the present study will provide a theoretical underpinning to potential cooperation between East Asian countries in
monitoring and controlling atmospheric conditions. |
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- Su-Jong Jeong, Chang-Hoi Ho, Sung-Deuk Choi, Jinwon Kim, Eun-Ju Lee, Hyeon-Ju Gim, 2013, Satellite Data-Based Phenological Evaluation of the
Nationwide Reforestation of South Korea, PLOS ONE, doi:10.1371/journal.pone.0058900
[abstract]
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Through the past 60 years, forests, now of various age classes, have been established in the southern part of the Korean
Peninsula through nationwide efforts to reestablish forests since the Korean War (1950–53), during which more than 65% of
the nation’s forest was destroyed. Careful evaluation of long-term changes in vegetation growth after reforestation is one of
the essential steps to ensuring sustainable forest management. This study investigated nationwide variations in vegetation
phenology using satellite-based growing season estimates for 1982–2008. The start of the growing season calculated from
the normalized difference vegetation index (NDVI) agrees reasonably with the ground-observed first flowering date both
temporally (correlation coefficient, r = 0.54) and spatially (r = 0.64) at the 95% confidence level. Over the entire 27-year
period, South Korea, on average, experienced a lengthening of the growing season of 4.5 days decade21, perhaps due to
recent global warming. The lengthening of the growing season is attributed mostly to delays in the end of the growing
season. The retrieved nationwide growing season data were used to compare the spatial variations in forest biomass carbon
density with the time-averaged growing season length for 61 forests. Relatively higher forest biomass carbon density was
observed over the regions having a longer growing season, especially for the regions dominated by young (,30 year)
forests. These results imply that a lengthening of the growing season related to the ongoing global warming may have
positive impacts on carbon sequestration, an important aspect of large-scale forest management for sustainable
development. |
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- Park, D.-S. R., C.-H. Ho, J.-H. Kim, and H.-S. Kim, 2013, Spatially inhomogeneous trends of tropical cyclone intensity over the western North Pacific for 1977-2010, Journal of Climate, In press, doi:10.1175/JCLI-D-12-00386.1
[abstract]
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The spatial distribution of trends in tropical cyclone (TC) intensity over the western North Pacific (WNP) during the period 1977-2010 was examined using five TC datasets. The spatial distribution of the TC intensity was expressed by seasonally averaged maximum wind speeds in 5°×5° horizontal grids. The trends show a spatial inhomogeneity, with a weakening in the tropical Philippine Sea (TP) and a strengthening in southern Japan and its southeastern ocean (SJ). This distribution can be described by TC intensification rate and genesis frequency, with the aid of the climatological direction of TC movement. The increasing intensification rate around the center of the WNP can mostly account for the increasing intensity over the SJ region due to the less genesis effect there, while the influence of both intensification rate and local genesis frequency matters in the TP region due to the effect of the newly generated and less developed weak TCs on the TC intensity. Thermodynamic variables (e.g., sea surface temperature, potential intensity, and 26°C isotherm depth) show almost homogeneous changes in space, possibly favoring intensification rate and genesis frequency over the entire WNP. However, the decreasing intensification rate and genesis frequency in some tropical regions conflict with the impact of thermodynamic variables, but rather accord with the impact of dynamic variables (i.e., vorticity and wind shear). In conclusion, the spatially inhomogeneous trends in TC intensity can be explained by considering the thermodynamic and dynamic aspects in combination through intensification rate and genesis frequency. |
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- Ho, C.-H., J.-H. Kim, H.-S. Kim, W. Choi, M.-H. Lee, H.-D. Yoo,T.-R. Kim, and S. Park, 2013, Technical note on a track-pattern-based model for predicting seasonal tropical cyclone activity over the western North Pacific, Adv. Atmos. Sci., 30, 1260-1274. doi:10.1007/s00376-013-2237-6
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- Kim, J.-H., C.-H. Ho, W. Choi and H.-S. Kim, 2012, 2010 Western North Pacific Typhoon Season: Seasonal Overview and Forecast using Track-pattern-based Model, Weather and Forecasting, 27, 730–743. doi:10.1175/WAF-D-11-00109.1.
[abstract]
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Fourteen named tropical cyclones (TCs) formed in the western North Pacific (WNP) in 2010, representing the lowest count since 1951. Both low activity during the typhoon season (June-October) and quiescence during the pre- and posttyphoon seasons were major contributing factors. Despite overall low activity, TC activity along land boundaries was enhanced because the overall genesis locations of TCs shifted to the north and west and a majority of them affected the coastal countries in the WNP. These features are attributed to the expansion of the subtropical high and weakening of the monsoon trough associated with the rapid transition of the 2009/10 El Nino to the 2010/11 La Nina. The National Typhoon Center (NTC) in South Korea utilizes the recently developed track-pattern-based model of the hybrid statistical-dynamical type as the operational long-range TC forecast system. This model fairly forecast the anomalous spatial distribution of TC track density for the 2010 typhoon season. A higher-than-normal track density was successfully forecast near Korea and Japan. This is attributed to the overall skillful forecast of TC count for each pattern by the NTC model, though some deficiencies in forecasting extremes for some patterns are evident. The total seasonal genesis frequency integrated over the seven patterns is well below normal (about 16.4) close to the observations. The fair predictability in 2010 using the NTC model is attributed to the skillful forecast of the ENSO transition by the National Centers for Environmental Prediction’s Climate Forecast System, in addition to the validity of the NTC model itself. |
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- Lee, M.-H., C.-H. Ho, J. Kim, and C.-K. Song, 2012, Assessment of the changes in extreme vulnerability over East Asia due to global warming, Climatic Change, 113(2), 301-321, doi: 10.1007/s10584-011-0345-9
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- Feng, S., C.-H. Ho, Q. Hu, R. J. Oglesby, S.-J. Jeong, and B.-M. Kim, 2012, Evaluating observed and projected future climate changes for the Arctic using the Köppen-Trewartha climate classification, Climate Dynamics, 38, 1359-1373, doi: 10.1007/s00382-011-1020-6
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- Jeong, J.-H., J.-S. Kug, B.-M. Kim, S.-K. Min, H. W. Linderholm, C.-H. Ho, D. Rayner, D. Chen, and S.-Y. Jun, 2012, Greening in the circumpolar high-latitude may amplify warming in the growing season, Climate Dynamics, 38, 1421x1431, doi: 10.1007/s00382-011-1142-x
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- Lee, M.-H., C.-H. Ho, J.-H. Kim, and H.-J. Song, 2012, Low-frequency variability of tropical cyclone-induced heavy rainfall over East Asia associated with tropical and North Pacific sea surface temperatures, Journal of Geophysical Research, 117, D12101, doi:10.1029/2012JD017565
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- Kim, H.-S., C.-H. Ho, J.-H. Kim, and P.-S. Chu, 2012, Track-pattern-based model for seasonal prediction of tropical cyclone activity over the western North Pacific, Journal of Climate, 25, 4660–4678. doi:10.1175/JCLI-D-11-00236.1.
[abstract]
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Skillful predictions of the seasonal tropical cyclone (TC) activity are important in mitigating the potential destruction from the TC approach/landfall in many coastal regions. In this study, a novel approach for the prediction of the seasonal TC activity over the western North Pacific is developed to provide useful probabilistic information on the seasonal characteristics of the TC tracks and vulnerable areas. The developed model, which is termed the “track-pattern-based model,” is characterized by two features: 1) a hybrid statistical=dynamical prediction of the seasonal activity of seven track patterns obtained by fuzzy c-means clustering of historical TC tracks and 2) a technique that enables researchers to construct a forecasting map of the spatial probability of the seasonal TC track density over the entire basin. The hybrid statistical-dynamical prediction for each pattern is based on the statistical relationship between the seasonal TC frequency of the pattern and the seasonal mean key predictors dynamically forecast by the National Centers for Environmental Prediction Climate Forecast System in May. The leave-one-out cross validation shows good prediction skill, with the correlation coefficients between the hindcasts and the observations ranging from 0.71 to 0.81. Using the predicted frequency and the climatological probability for each pattern, the authors obtain the forecasting map of the seasonal TC track density by combining the TC track densities of the seven patterns. The hindcasts of the basinwide seasonal TC track density exhibit good skill in reproducing the observed pattern. The El Nino/La Nina-related years, in particular, tend to show a better skill than the neutral years. |
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- Jeong, S.-J., C.-H. Ho, B.-M.Kim, S. Feng, and D. Medvigy, 2012, Nonlinear response of vegetation to coherent warming over northern high latitudes, Remote Sensing Letters, 4(2), 123-130
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- Ho, C.-H., S.-J. Park, S.-J. Jeong, J. Kim, and J.-G. Jhun, 2012, Observational evidences of double cropping impacts on the climate in the northern China plains, Journal of Climate , 25, 4721–4728.
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- Lee, Y.-G., C.-H. Ho, J. Kim, J. Kim, 2012, Potential impacts of northeastern Eurasian snow cover on generation of dust storms in northwestern China during spring, Climate Dynamics, doi: 10.1007/s00382-012-1522-x
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- Song, U., S. Mun, C.-H. Ho, and E.-J. Lee, 2012, Responses of two invasive plants under various microclimate conditions in the Seoul metropolitan region, Environmental Management, 49, 1238–1246, doi: 10.1007/s00267-012-9852-3
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- Park, J.-H., M.-L. Ou, S. Kim, and H. Cho, 2012, Sensitivity of satellite-derived wind retrieval over cloudy scenes to target selection in tracking and pixel selection in height assignment, IEEE Transactions on Geoscience and Remote Sensing, 50(5), 2063–2073
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- Cho, H., C.-H. Ho, and Y.-S. Choi, 2012, The observed variation in cloud-induced longwave radiation in response to sea surface temperature over the Pacific warm pool from MTSAT-1R imagery, Geophysical Research Letters, 39, L18802. doi:10.1029/2012GL052700
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- Park, C.-E., C.-H. Ho, S.-J. Jeong, J. Kim, and S. Feng, 2012, The potential of vegetation feedback to alleviate climate aridity over the United States associated with a 2xCO2 climate condition, Climate Dynamics, 38, 1489-1500, doi: 10.1007/s00382-011-1150-x
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- Kim, J.-H., C.-C. Wu, C.-H. Sui, and C.-H. Ho, 2012, Tropical cyclone contribution to the interdecadal change in summer rainfall over South China in the early 1990s, Terrestrial, Atmospheric and Oceanic Sciences, 23, 49-58, doi: 10.3319/TAO.2011.08.26.01(A)
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- Ho, C.-H., T.-W. Park, S.-Y. Jun, M.-H. Lee, C.-E. Park, J. Kim, S.-J. Lee, Y.-D. Hong, C.-K. Song, and J.-B. Lee, 2011, A projection of extreme climate events in the 21st century over East Asia using the Community Climate System Model 3, Asian-Pacific Journal of Atmospheric Sciences, 47(4), 329-344, doi:10.1007/s13143-011-0020-0.
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- Jeong, S.-J., C.-H. Ho, M. Brown, J.-S. Kug, and S. Piao , 2011, Browning in desert boundaries over Asia in the recent decades , Journal of Geophysical Research, VOL. 116, D02103, 7 PP., 2011
doi:10.1029/2010JD014633
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- Park, T-W, C.-H. Ho, S.-J Jeong, Y.-S. Choi, S. K. Park, and C.-K. Song, 2011, Different Characteristics of Cold Day and Cold Surge Frequency over East Asia in a Global Warming Situation, Journal of Geophysical Research , 116, D12118, doi:10.1029/2010JD015369
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- Park, M.-S., C.-H. Ho, J. Kim, R. L. Elsberry, 2011, Diurnal circulations and their multi-scale interaction leading to rainfall over the South China Sea upstream of the Philippines during intraseasonal monsoon westerly wind bursts, Climate Dynamics, 37, 1483-1499, DOI:10.1007/s00382-010-0922-z
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- Lee, S., C.-H. Ho, and Y.-S. Choi, 2011, High-PM10 concentration episodes in Seoul, Korea: Background
sources and related meteorological conditions, Atmospheric Environment, 45, 7240-7247
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- Cha, D.-H., C.-S. Jin, D.-K. Lee, and Y.-H. Kuo, 2011, Impact of intermittent spectral nudging on regional climate simulation using Weather Research and Forecasting model., Journal of Geophysical Research, 116, D10103, doi:10.1029/2010JD015069
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- Cha, D.-H., C.-S. Jin, and D.-K. Lee, 2011, Impact of local sea surface temperature anomaly over the western North Pacific on extreme East Asian summer monsoon., Climate Dynamics, 37, 1691–1705, doi:10.1007/s00382-010-0983-z
[abstract]
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In this study, the anomalous characteristics of observed large-scale synoptic fields in the extreme East Asian summer monsoon (EASM) years are analyzed, and the impact of the local sea surface temperature (SST) anomaly over the western North Pacific (WNP) on the extreme EASM is investigated through sensitivity experiments of 28 years EASM simulations to the local SST over the WNP. The observation analysis reveals that the extreme EASM is influenced more by anomalous large-scale atmospheric features such as monsoon circulations and the western North Pacific subtropical high than the local SST anomaly over the WNP. However, the results of the sensitivity experiments show that the local SST anomaly has an implicit impact on the extreme EASM. The patterns of differences in precipitation between the experiment forced by observed SST in each year and the experiment forced by climatological SST over the WNP are opposite to anomaly patterns of observed precipitation in the extreme EASM years. This is because the SST anomaly over the WNP plays a role in reducing precipitation anomaly by hanging surface latent heat flux and monsoon circulations. In particular, the local SST anomaly over the WNP decreases anomalies of large-scale circulations, i.e., the local Hadley and the Walker circulations. Thus, the local SST anomaly over the WNP plays a role in decreasing the interannual variability of the EASM. |
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- Jeong, J.-H., C.-H. Ho, S.-J. Jeong, Y.-S. Choi, H. Linderholm, and D. Chen, 2011, Impact of urban warming on earlier spring flowering in Korea, International Journal of Climatology, Online first, doi: 10.1002/joc.2178
[abstract]
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Using long-term (1954-2004) observations of four selected species in South Korea: goldenbell (Forsythia koreana), azalea (Rhododendron mucronulatum), cherry (Prunus yedoensis), and peach (Prunus persica), the impact of urban warming on spring flowering was investigated. Trends of early spring temperatures and first-flowering dates (FFDs) of the four plants were cross-compared among nine differently urbanized cities. It was clearly observed that urban warming has led to an advance in the timing of first-flowering of several days to weeks during recent decades, while the intrinsic physiology of plants to sense thermal energy has not been changed. The degree of advancement of the FFD was observed to be roughly proportional to degree of urbanization. Moreover, the sensitivity of the FFD to urban warming was estimated to be higher for the shrub species (-9.07 and -6.64 days °C−1 for goldenbell and azalea, respectively) than the tree species (−2.46 and −2.90 days °C−1 for peach and cherry, respectively). Our results suggest that the impact of urban warming should be considered as an influential factor which drives changes in the regional natural environment, especially in regions of rapid urbanization. |
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- Jeong, S.-J., C.-H. Ho, T.-W Park, J. Kim, and S. Levis, 2011, Impact of vegetation feedback on the temperature and its diurnal range over the Northern Hemisphere during summer in a 2xCO2 climate, Climate Dynamics, Online first, doi:10.1007/s00382-010-0827
[abstract]
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This study examines the potential impact of vegetation feedback on the changes in the diurnal temperature range (DTR) due to the doubling of atmospheric CO2 concentrations during summer over the Northern Hemisphere using a global climate model equipped with a dynamic vegetation model. Results show that CO2 doubling induces significant increases in the daily mean temperature and decreases in DTR regardless of the presence of the vegetation feedback effect. In the presence of vegetation feedback, increase in vegetation productivity related to warm and humid climate lead to (1) an increase in vegetation greenness in the mid-latitude and (2) a greening and the expansion of grasslands and boreal forests into the tundra region in the high latitudes. The greening via vegetation feedback induces contrasting effects on the temperature fields between the mid- and high-latitude regions. In the mid-latitudes, the greening further limits the increase in T max more than T min, resulting in further decreases in DTR because the greening amplifies evapotranspiration and thus cools daytime temperature. The greening in high-latitudes, however, it reinforces the warming by increasing T max more than T min to result in a further increase in DTR from the values obtained without vegetation feedback. This effect on T max and DTR in the high latitude is mainly attributed to the reduction in surface albedo and the subsequent increase in the absorbed insolation. Present study indicates that vegetation feedback can alter the response of the temperature field to increases in CO2 mainly by affecting the T max and that its effect varies with the regional climate characteristics as a function of latitudes.
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- Rui, M., C.-H. Ho, Y. Shao, D.-Y. Gong, J. Kim, 2011, Influence of Arctic Oscillation on Dust Activity over Northeast Asia, Atmospheric Environment, 45(2), 326-337
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- Kim, H.-S., J.-H. Kim, C.-H. Ho, and P.-S. Chu, 2011, Pattern classification of typhoon tracks using the fuzzy c-means clustering method, Journal of Climate, 24(2), 488-508, doi: 10.1175/2010JCLI3751.1
[abstract]
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A fuzzy c-means clustering method (FCM) is applied to cluster tropical cyclone (TC) tracks. FCM is suitable for the data where cluster boundaries are ambiguous, such as a group of TC tracks. This study introduces the feasibility of a straightforward metric to incorporate the entire shapes of all tracks into the FCM, i.e., the interpolation of all tracks into equal number of segments. Four validity measures (e.g., partition coefficient, partition index, separation index, and Dunn index) are used objectively to determine the optimum number of clusters. This results in seven clusters from 855 TCs over the western North Pacific (WNP) from June through October during 1965–2006. The seven clusters are characterized by 1) TCs striking Korea and Japan with north-oriented tracks, 2) TCs affecting Japan with long trajectories, 3) TCs hitting Taiwan and eastern China with west-oriented tracks, 4) TCs passing the east of Japan with early recurving tracks, 5) TCs traveling the easternmost region over the WNP, 6) TCs over the South China Sea, and 7) TCs moving straight across the Philippines. Each cluster shows distinctive characteristics in its lifetime, traveling distance, intensity, seasonal variation, landfall region, and distribution of TC-induced rainfall. We also discuss the roles of large-scale environments (e.g., sea surface temperatures, low-level relative vorticity and steering flows) on cluster-dependent genesis locations and tracks.
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- Jeong, S.-J., C.-H. Ho, H.-J.Gim, and M. Brown, 2011, Phenology shifts at start versus end of growing season in temperate vegetation over the Northern Hemisphere for the period 1982-2008, Global Change Biology (online first), doi: 10.1111/j.1365-2486.2011.02397.x.
[Faculty of 1000 selection]
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- Ho, C.-H., and H.-S. Kim, 2011, Reexamination of the influence of ENSO on landfalling tropical cyclones in Korea, Asia-Pacific Journal of Atmospheric Sciences, 47(5), 457-462, doi: 10.1007/s13143-011-0030-y
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- Park, T.-W., C.-H. Ho, and S. Yang, 2011, Relationship between Arctic Oscillation and Cold Surges over East Asia, Journal of Climate, 24(1), 68-83
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- Park, D.-S. R., C.-H. Ho, J.-H. Kim, and H.-S. Kim , 2011, Strong landfall typhoons in Korea and Japan in a recent decade, Journal of Geophysical Research, 116, D07105, doi:10.1029/2010JD014801
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- Lee Y.-K., S.W. Yeh, Boris D., B.-K. Moon, and J.-G. Jhun, 2011, The influences of interannual stratification variability and wind stress forcing on ENSO before and after the 1976 climate shift, Theoretical and Applied Climatology, 107, 623-631, doi: 10.1007/s00704-011-0514-9
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- Choi, Y.-S., C.-H. Ho, S.-W. Kim, and R. S. Lindzen, 2010, Abundant supercooled clouds in the winter Antarctic atmosphere observed in MODIS and CALIOP measurements, Advances in Atmospheric Science, 27(6), 1233-1245
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- Chu P.-S., X. Zhao, C.-H. Ho, H.-S. Kim, M.-M. Lu, and J.-H. Kim, 2010, Bayesian forecasting of seasonal typhoon activity: A track-pattern-oriented categorization approach for Taiwan, Journal of Climate, 23(24), 6654–668, doi: 10.1175/2010JCLI3710.1
[abstract]
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A new approach to forecasting regional and seasonal tropical cyclone (TC) frequency in the western North Pacific using the antecedent large-scale environmental conditions is proposed. This approach, based on TC track types, yields probabilistic forecasts and its utility to a smaller region in the western Pacific is demonstrated. Environmental variables used include the monthly mean of sea surface temperatures, sealevel pressures, low-level relative vorticity, vertical wind shear, and precipitable water of the preceding May. The region considered is the vicinity of Taiwan and typhoon season runs from June through October. Specifically, historical TC tracks are categorized through a fuzzy clustering method into seven distinct types. For each cluster, a Poisson or probit regression model cast in the Bayesian framework is applied individually to forecast the seasonal TC activity. With a noninformative prior assumption for the model parameters, and following Chu and Zhao (2007) for the Poisson regression model, a Bayesian inference for the probit regression model is derived. A Gibbs sampler based on the Markov Chain Monte Carlo method is designed to integrate the posterior predictive distribution. Because the cluster 5 is the most dominant type affecting Taiwan, a leave-one-out cross-validation procedure is applied to predict seasonal TC frequency for this type for the period of 1979–2006 and the correlation skill is found to be 0.76 |
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- Kim, J.-H., C.-H. Ho, and P.-S. Chu , 2010, Dipolar redistribution of summertime tropical cyclone genesis between the Philippine Sea and the northern South China Sea and its possible mechanism, Journal of Geophysical Research, 115, D06104, doi:10.1029/2009JD012196.
[abstract]
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Recent observational records show that the dipole oscillation between the Philippine Sea (PS) and the northern South China Sea (nSCS) is a leading empirical orthogonal function (EOF) of summertime tropical cyclone (TC) genesis in the western North Pacific (WNP). This PS-nSCS oscillation is characterized by a distinguished decadal variability in addition to an interannual variability. Meanwhile, the typical El Nino/Southern Oscillation (ENSO)-related mode is found in the second EOF mode, which is predominantly interannual. With regard to the PS-nSCS oscillation, its interannual component appears to be linked with the previous wintertime ENSO event, but the linkage is not so robust in the sense that about half of its significant events are classified as the ENSO-related case, whereas its decadal component is coupled to a sea surface temperature anomaly (SSTA) in the central Pacific with its equatorial core near the Nino-4 region, which is flanked by an opposite SSTA on both sides along the latitudinal belt. Interestingly, this SSTA pattern resembles that related to the ENSO Modoki, and equivalently, the transitional phase of ENSO. The ENSO Modoki is regionally manifested by the anomalous zonal SST gradient between the equatorial western and central Pacific; thus the decadal modulation of this anomalous zonal SST gradient can be regarded as an actual forcing that forms and modulates the decadal PS-nSCS oscillation. In addition, the decadal PS-nSCS oscillation is compared with the decadal basin-wide TC genesis variation in terms of the Pacific SSTA pattern and the associated anomalous large-scale environments. |
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- Lee, M.-H., C.-H. Ho, and J.-H. Kim, 2010, Influence of tropical cyclone landfalls on spatiotemporal variations in typhoon season rainfall over South China, Advances in Atmospheric Sciences, 27(2), 443–454.
[abstract]
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This study examined the impact of tropical cyclone (TC) landfalls on the spatiotemporal variations in the rainfall over South China for the period 1957-2005. The target region was selected to show the noteworthy contribution of TC landfalls to the total rainfall during the typhoon season (July-October). Two prevailing spatial variations in the rainfall were obtained from an empirical orthogonal function (EOF) analysis. The first EOF mode displays single-sign variability over South China with an explained variance of 23.4%. The associated time series of this mode fluctuates on a decadal timescale and was found to be correlated with the TC genesis in the South China Sea. The second EOF mode shows a seesaw pattern between Hainan Island/Guangdong Province and the remaining regions with an explained variance of 11.4%. This seesaw pattern results from an anti-correlation in seasonal TC landfalls between two regions, which was found in previous studies. This is related to the strengthening (weakening) of the upper tropospheric jets and the corresponding development of a massive anticyclonic (cyclonic) circulation over East Asia. The EOF analysis was also conducted using just the data of rainfall caused by TC landfall. This revealed that the first EOF mode with just the TC-induced rainfall is nearly identical to the second mode with the total rainfall. The obvious seesaw pattern of the first mode when applying just the TC-induced rainfall to the EOF analysis implies that this pattern has a larger temporal variation than the single-signed pattern (i.e., the first EOF mode using the total rainfall) in terms of TC landfalls. This study suggests that TC landfalls over South China and the accompanying rainfall significantly modulate the spatial variation of the typhoon season rainfall there. |
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- Park, T.-W., C.-H. Ho, S. Yang, and J.-H. Jeong, 2010, Influences of the AO and the MJO on cold surges and heavy snowfalls over Korea: A cast study during 2009/10 winter, Journal of Geophysical Research, 115, D23122, doi:10.1029/2010JD014794
[abstract]
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In the winter of 2009–2010, frequent and long‐lasting cold weather affected Korea. Four major cold surges and several heavy snowfall events were observed, including a record‐breaking event on 4 January 2010. These four cold surges had distinct properties with regard to their relationships to the phases of the Arctic Oscillation (AO) and the Madden‐Julian Oscillation (MJO), suggesting the possible influences of the AO and MJO on the cold surges and heavy snowfalls. The four cold surges were of two distinct types: the wave train type and the blocking type, which were differentiated by their mechanisms. With regard to the relationships of the cold surges to the AO, three cold surges occurred during a strongly negative AO period, which lasted for more than 1 month. The Siberian High expanded from the Arctic high‐pressure region to East Asia during the negative AO period. A cold surge occurred during a positive AO, with the expansion of the Siberian High across the Eurasian continent. An MJO‐induced circulation, corresponding to strong tropical convection over the tropical Indian Ocean, seems to have reinforced the cold surges over East Asia. In addition, the active local Hadley circulation modulated by a convection center over the Indian Ocean tends to enhance midlatitude synoptic disturbances across East Asia and provides favorable conditions for upward motion over the region. In short, the effects of the AO and MJO, along with the existing low‐level moisture supply, contributed to heavy snowfalls associated with strong cold surges over Korea during the winter of 2009–2010. |
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- Yoo,S.-H., J. Fasullo, S. Yang, and C.-H. Ho, 2010, On the relationship between Indian Ocean sea surface temperature and the Transition from El Nino to La Nina, Journal of Geophysical Research, 115, D15114, doi:10.1029/2009JD012978.
[abstract]
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The relationship between Indian Ocean sea surface temperature and the transition of El Niño events into either La Niña or El Niño–Southern Oscillation neutral conditions is examined in both observations and the retrospective ensemble hindcasts of the National Center for Environmental Prediction Climate Forecast System. The southern Indian Ocean is shown to demonstrate a particularly robust and consistent relationship with the evolution of these transitions. These associations are described, and a physical mechanism involving air-sea interaction in the Indian and western Pacific Oceans is proposed. Observations suggest that easterly surface wind anomalies in the western Pacific Ocean are associated with the emergence of La Niña during boreal summer and fall. Here it is shown that these winds are significantly correlated to southern Indian Ocean sea surface temperature in the preceding spring that is characterized by a large-scale zonal dipole of cool and warm anomalies in the southwestern and southeastern Indian Oceans, respectively. These associations are particularly pronounced for strong El Niño conditions, during the dissipation of which a pronounced wavetrain-like atmospheric pattern accompanies sea surface temperature anomalies in the southern Indian Ocean. Together, the circulation and sea surface temperature anomalies increase the meridional cross-equatorial temperature gradient in the western Indian Ocean and mute intraseasonal variability while strengthening surface equatorial easterly winds in the Indo-Pacific warm pool. Collectively, these anomalies favor subsequent La Niña development. On the basis of these observed associations, a predictive model that demonstrates skill in anticipating the nature of El Niño transitions, involving the southern Indian Ocean, Asian monsoon, and El Niño–Southern Oscillation, is proposed. In the National Center for Environmental Prediction Climate Forecast System, the relationships described above are simulated both consistently and realistically, despite model weaknesses, further bolstering a key role of southern Indian Ocean and predictive relationship. Comparison of fully coupled and sea surface temperature–forced simulations suggests a key role for air-sea interaction in the observed associations. Moreover, it is demonstrated that coupled simulations of El Niño–Southern Oscillation may benefit substantially from improved representation of Indian Ocean variability and Indo-Pacific interaction. |
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- Jeong, S.-J., C.-H. Ho, K.-Y.Kim, J.-H. Jeong, J. Kim, and T.-W. Park, 2010, Potential impact of vegetation feedback on European heat wave in a doubled-CO2 climate, Climatic Change, 99, 625-635.
[abstract]
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Inclusion of the effects of vegetation feedback in a global climate change simulation suggests that the vegetation–climate feedback works to alleviate partially the summer surface warming and the associated heat waves over Europe induced by the increase in atmospheric CO2 concentrations. The projected warming of 4°C over most of Europe with static vegetation has been reduced by 1°C as the dynamic vegetation feedback effects are included.. Examination of the simulated surface energy fluxes suggests that additional greening in the presence of vegetation feedback effects enhances evapotranspiration and precipitation, thereby limiting the warming, particularly in the daily maximum temperature. The greening also tends to reduce the frequency and duration of heat waves. Results in this study strongly suggest that the inclusion of vegetation feedback within climate models is a crucial factor for improving the projection of warm season temperatures and heat waves over Europe. |
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- Park, S.-J., S.-U. Park, and C.-H. Ho, 2010, Roughness Length of Water Vapor over Land Surfaces and Its Influence on Latent Heat Flux, Terrestrial, Atmospheric and Oceanic Sciences , 21(5), doi: 10.3319/TAO.2009.11.13.01(Hy)
[abstract]
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Latent heat flux at the surface is largely dependent on the roughness length for water vapor (z0q). The determination of z0q is still uncertain because of its multifaceted characteristics of surface properties, atmospheric conditions and insufficient observations. In this study, observed values from the Fluxes Over Snow Surface II field experiment (FLOSS-II) from November 2002 to March 2003 were utilized to estimate z0q over various land surfaces: bare soil, snow, and senescent grass. The present results indicate that the estimated z0q over bare soil is much smaller than the roughness length of momentum (z0m); thus, the ratio z0m/z0q is larger than those of previous studies by a factor of 20 - 150 for the available flow regime of the roughness Reynolds number, Re* > 0.1. On the snow surface, the ratio is comparable to a previous estimation for the rough flow (Re* > 1), but smaller by a factor of 10 - 50 as the flow became smooth (Re* < 1). Using the estimated ratio, an optimal regression equation of z0m/z0q is determined as a function of Re* for each surface type. The present parameterization of the ratio is found to greatly reduce biases of latent heat flux estimation compared with that estimated by the conventional method, suggesting the usefulness of current parameterization for numerical modeling. |
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- Choi, Y.-S., C.-H. Ho, J. Kim, and R. S. Lindzen, 2010, Satellite retrievals of (quasi-)spherical particles at cold temperatures, Geophysical Research Letters, 37, L05703, doi:10.1029/2009GL041818
[abstract]
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Measurements from NASA's A-train satellites indicate that spherical or quasi-spherical particles may constitute up to 30% of the total cloud particles at temperatures below −30°C, and up to 10% even for temperatures below −40°C, the temperature range typically found in the upper troposphere and the lower stratosphere. Current climate models calculate cloud radiative forcing on the basis on an assumption that essentially no spherical or quasi-spherical particles exist below −40°C (even below −15°C). The findings in this study show that this widely used assumption in climate models may need re-examination. Further research is also needed to confirm and quantify these findings, especially improvements in the satellite retrievals of cloud particle shapes that, in the mean, currently contain about 10% uncertainties.
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- Kim, H.-S., C.-H. Ho, P.-S. Chu, and J.-H. Kim, 2010, Seasonal prediction of summertime tropical cyclone activity over the East China Sea using the least absolute deviation regression and the Poisson regression, International Journal of Climatology, 30(2), 210-219, doi:10.1002/joc.1878.
[abstract]
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In the present study, we have employed two statistical models to predict summertime
(July-September) tropical cyclone (TC) activity over the East China Sea using the least
absolute deviation (LAD) regression and the Poisson regression method. Through a lagged correlation analysis of the relationship between the seasonal TC frequency in the target region and several pre-season environmental parameters for the period 1979-2003,
physically interpretable and statistically significant large-scale environmental parameters
were identified as potential predictors. After applying the predictor screening method based on the stepwise regression, three predictors, i.e. sea surface temperature, outgoing
long-wave radiation and 850-hPa relative vorticity were finally chosen. They are related
to the phase transition of El Nino/Southern Oscillation and the strength of the western
North Pacific summer monsoon. The correlation coefficient between the predicted and
the observed frequency is 0.75 for the LAD model and 0.78 for the Poisson model.
The predictions using the two models have a skill improvement of about 60% compared
to the reference forecasts. The present study suggests that both models are skillful
in predicting summertime TC frequency over the East China Sea with the Poisson model
being slightly more skillful than the LAD model.. |
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- Choi, Y.-S., R. S. Lindzen, C.-H. Ho, J. Kim, 2010, Space observations of cold-cloud phase change, PNAS, 107(25), 11211-11216
[abstract]
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This study examines the vertically resolved cloud measurements from the cloud-aerosol lidar with orthogonal polarization instrument on Aqua satellite from June 2006 through May 2007 to estimate the extent to which the mixed cloud-phase composition can vary according to the ambient temperature, an important concern for the uncertainty in calculating cloud radiative effects. At -20 °C, the global average fraction of supercooled clouds in the total cloud population is found to be about 50% in the data period. Between -10 and -40 °C, the fraction is smaller at lower temperatures. However, there are appreciable regional and temporal deviations from the global mean (> ± 20%) at the isotherm. In the analysis with coincident dust aerosol data from the same instrument, it appears that the variation in the supercooled cloud fraction is negatively correlated with the frequencies of dust aerosols at the -20 °C isotherm. This result suggests a possibility that dust particles lifted to the cold cloud layer effectively glaciate supercooled clouds. Observations of radiative flux from the clouds and earth’s radiant energy system instrument aboard Terra satellite, as well as radiative transfer model simulations, show that the 20% variation in the supercooled cloud fraction is quantitatively important in cloud radiative effects, especially in shortwave, which are 10 - 20 W m-2 for regions of mixed-phase clouds affected by dust. In particular, our results demonstrate that dust, by glaciating supercooled water, can decrease albedo, thus compensating for the increase in albedo due to the dust aerosols themselves. This has important implications for the determination of climate sensitivity. |
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- Chen, D., T. Ou, L. Gong, C.-Y. Xu, W. Li, C.-H. Ho and W. Qian, 2010, Spatial interpolation of daily precipitation in China: 1951-2005, Advances in Atmospheric Sciences, 27(6),1221-123
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- Choi, Y.-S., C.-H. Ho, D.-Y. Gong, J.-H. Jeong, and T.-W. Park, 2009, Adaptive change in intra-winter distribution of relatively cold events to East Asian warming, Terrestrial, Atmospheric and Oceanic Sciences, 20(6), 807-816
[abstract]
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For the past few decades, the daily winter temperatures over East Asia have been higher and less variable. Generally, these simple temperature-distribution shifts should lead to a decrease in the occurrence of cold extremes, but observations of the changes in the extremes are often complicated. In the present study, the change in the occurrence of relatively cold events (daily temperature anomaly, 2σ for that season) in each winter monsoon over East Asia was examined using ground observations of daily temperature for the period 1954-2006. The time-mean temperature for each winter was subtracted to remove the interannual variability and long-term trend. Our analyses reveal that the intraseasonal temperature distribution over East Asia has changed with a negatively skew, and the frequency of the relatively cold events has slightly increased (by 0.09 days per decade) over the past few decades, on an average, for the entire analysis domain (east of 105E, 122 stations). In particular, the increase occurs more dominantly (82% of the total stations) in regions north of 40N where a stronger warming has progressed. The frequency of relative cold events is found to be significantly correlated with the variance of Siberian high and the mean of the Arctic Oscillation. The increasing trend in the frequency of relatively cold events may serve to partly countervail the decrease -1.12 days per decade) in the frequency of absolute 2σ overall) across the entire observation period. |
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- Gong, D.-Y., S.-J. Kim, and C.-H. Ho, 2009, Arctic and Antarctic Oscillation signatures in tropical coral proxies over the South China Sea, Annales Geophysicae, 27, 1979–1988
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- Choi, Y.-S., R. Park, and C.-H. Ho, 2009, Estimates of ground-level aerosol mass concentrations using a chemical transport model with Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol observations over East Asia, Journal of Geophysical Research, 114, D04204, doi:10.1029/2008JD011041
[abstract]
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We estimate ground-level mass concentrations of PM2.5 and PM10 (particulate matter smaller than 2.5 and 10 μm in diameter, respectively) for 2001 using a global chemical transport model with Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth (AOD) retrievals. Our method improves on previous techniques by using a new satellite product (fine-mode fraction (FMF)) and is applied to East Asia, where such an approach has not previously been attempted. We evaluate the method by comparing the PM estimates with the observations from Air Quality System sites and Acid Deposition Monitoring Network sites across East Asia. The spatial patterns of the annual and seasonal means of the estimated PM10 concentrations are in better agreement with the observations than the results of the model alone. The PM2.5 estimates based on both MODIS AOD and FMF data show considerable improvement relative to those using AOD data alone or simply the model and are in better agreement with the observations at three available sites in Korea and Japan. The greatest improvement is found in the cases where the model significantly underestimates the data. Our best estimates of the annual mean PM2.5 and PM10 concentrations over East Asia are 14.7 and 71.2 μg m-3, respectively. However, the uncertainties in our PM2.5 and PM10 estimates are up to 2.5 and 20 μg m-3, respectively.
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- Choi, Y.-S., C.-H. Ho, H.-R. Oh, R. J. Park, and C.-G. Song, 2009, Estimating bulk optical properties of aerosols over the western North Pacific by using MODIS and CERES measurements, Atmospheric Environment , 43, 5654-5660, doi:10.1016/j.atmosenv.2009.07.036
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- Park, S.-J., S.-U. Park, C.-H. Ho, and Larry Mahrt, 2009, Flux-Gradient Relationship of Water Vapor in the Surface Layer Obtained from CASES-99 Experiment, Journal of Geophysical Research, 114, D08115, doi:10.1029/2008JD011157
[abstract]
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The flux-gradient relationship of water vapor was obtained from the Cooperative Atmosphere-Surface Exchange Study-1999 (CASES-99) field experiment, which was conducted on a flat and grassy field in the southeastern part of Kansas, USA, during October 1999. The CASES-99 data include turbulence measurements of wind, temperature, and vapor density along with their time-averaged values at various levels above the ground. Quality control of the data on the turbulent wind velocity, sonic temperature, and vapor density was performed prior to flux calculation. The turbulent sensible heat and latent heat fluxes were calculated using a 30-minute window, and they were subsequently corrected and checked for the fulfillment of the steady-state and for turbulence intensity. Weak fluxes and through-tower wind data were also excluded from the analysis. Vertical gradients of the mean values were obtained by differentiating functions fitted to the measured mean profiles. It was found that the flux-gradient relationship value of water vapor is comparable to that of temperature for weakly stable stratification and less than that of temperature for strongly stable stratification. On the contrary, the flux-gradient relationship value of water vapor was found to be larger than that of temperature by approximately 20% for the neutral and unstable stratifications. The best-fitting functions for water vapor are found to be Φq = 1.21(1 - 13.1z/L)^1/2 and Φq = 1.21(1 + 60.4z/L)^1/3 for the unstable and stable stratifications, respectively. |
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- Jeong, S.-J., C.-H. Ho, and J.-H. Jeong,, 2009, Increase in vegetation greenness and decrease in springtime warming over East Asia, Geophysical Research Letters, 36, L02710
[abstract]
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This study investigates the impact of increased vegetation greening on the springtime temperature over east Asia for 1982–2000. An analysis of station-based temperature records and satellite-measure normalized difference vegetation index (NDVI) indicates that slight warming (<0.4°C 10-yr) occurred over regions that experienced large increase in NDVI (≥0.08 10-yr). On the contrary, strong warming (≥0.8°C 10-yr) occurred over regions that exhibited minor changes in NDVI (<0.04 10-yr). For the most part, this inverse NDVI & temperature relationship observed with the daily maximum temperature. Thus, it is suggested that the decrease in warming was mostly attributable to the increase in evapotranspiration associated with increased vegetation greening. Earlier vegetation growth may have further strengthened the effect of this vegetation–evaporation on spring temperature. |
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- Ho, C.-H., H.-S. Kim, J.-H. Jeong, and S.-W. Son, 2009, Influence of stratospheric Quasi-Biennial Oscillation on tropical cyclone tracks in western North Pacific, Geophysical Research Letters, 36, L06702, doi:10.1029/2009GL037163
[abstract]
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The possible influence of the stratospheric quasi-biennial oscillation (QBO) on
tropical cyclone (TC) passages in the western North Pacific (WNP) is examined using TC
data recorded by the Tokyo Typhoon Center and the QBO index derived from reanalysis
data. The influence is observed to be significant. The number of TCs approaching the
East China Sea is large during the westerly phase of the QBO; however, during the
easterly phase, the number of TCs approaching the eastern offshore of Japan is large.
This difference in the TC tracks is found to be related to the background flow change
associated with the QBO. However, the total number of TC events over the WNP and the
sum of the number of TCs approaching the aforementioned two regions appear to be
unrelated to the QBO phases. |
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- Ho, C.-H., Y.-S. Choi, and S.-K. Hur, 2009, Long-term changes in summer weekend effect over northeastern China and the connection with regional warming
, Geophysical Research Letter, 36, L15706, doi:10.1029/2009GL039509
[abstract]
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The 7-day cycle of human activities may lead to the “weekend effect” in climate variables and air pollutants; this effect is defined as the average value for Saturday through Monday minus the average value for Wednesday through Friday. The weekend effect is a consequence of complex aerosol-meteorology interactions, particularly involving changes in cloud and relative humidity. Over northeastern China during three recent decades (19802005), the weekend effect in the diurnal temperature range significantly increased; conversely, the weekend effects in the relative humidity, cloud amount, and light rain (£5 mm day–1) events significantly decreased. These long-term changes in the weekend effects have a high correlation coefficient (r) with the decrease in relative humidity (|r| ≈ 0.7–0.8), which is likely induced by regional warming over the region. The results suggest that regional warming may largely be responsible for a shift of dominant aerosol effects on a weekly timescale. |
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- Jeong, S.-J., C.-H. Ho, K.-Y.Kim, and J.-H. Jeong, 2009, Reduction of spring warming over East Asia associated with vegetation feedback, Geophysical Research Letters , 36, L18705, doi:10.1029/2009GL039114.
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- Ho, C.-H., H.-S. Kim, and P.-S. Chu, 2009, Seasonal Prediction of Tropical Cyclone Frequency over the East China Sea through a Bayesian Poisson-Regression Method, Asia-Pacific Journal of Atmospheric Sciences, 45(1), 45-54.
[abstract]
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In this study, a Bayesian method has been used to predict the seasonal number of tropical cyclones (TCs) over the East China Sea (25°N-35°N, 120°E-130°E). The method considers two periods each year and provides several different predictions of the number of TCs that will enter the target area during a typhoon season, assigning a probability value to indicate the likelihood of each prediction. The method was used to forecast the number of TCs that would occur over the extended season (June - September) issued by June 1 and over the peak season (July - September) issued by July 1. The three parameters of sea surface temperature (SST), outgoing longwave radiation (OLR), and 850-hPa vorticity (VOR850) were used as predictors, based on lag correlation coefficients with the TCs over the target region for 1979-2003. For the extended season prediction, the SST for February - April, the VOR850 for February 16 - May 15, and the OLR for May 1 - May 15 were chosen as predictors in the TC forecast system. The three predictors for the peak season prediction are delayed one month relative to those for the extended season prediction. The observed TCs over the target region mainly fall into the prediction range within 25% probability from the median during the period from 1979 to 2007. The method predicts the mean TC frequency with a high level of accuracy, yielding a correlation coefficient of 0.69 and 0.71 and a root mean square error of 1.48 and 1.20 between the predicted and observed TCs for the extended and peak season forecasts, respectively. This TC prediction method may soon be used for operational purposes. |
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- Song, C.-K., C.-H. Ho, R. J. Park, Y.-S. Choi, J. Kim, D.-Y. Gong, and Y.-B. Lee, 2009, Spatial and Seasonal Variations of Surface PM10 Concentration and MODIS Aerosol Optical Depth over China, Asia-Pacific Journal of Atmospheric Sciences, 45(1), 33-43.
[abstract]
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We examine the spatial and temporal variabilities of ground-observed concentrations of particulate matter with diameters ≤ 10 μm (PM10) over China and compare them with satellite-retrieved data on the aerosol optical depth (AOD) collected over the period 2003-2005 using a moderate resolution imaging spectroradiometer (MODIS). Annual mean values of the PM10 concentrations and AOD show a strong spatial correlation, indicating the consistent presence of aerosol concentrations. However, the
temporal correlation between the monthly values of the PM10 concentrations and AOD indicates a regional contrast in their seasonality. The correlation coefficients are 0.6 or higher in the southeastern coast region, whereas they are -0.6 or lower in the north-central region. The regional discrepancy is probably caused by the difference in the size distributions of aerosols. This is also supported by the data on the distribution of the Angstrom exponent and fine mode fraction obtained from the MODIS. The characteristics of the aerosols with respect to coarse and fine particles are discussed in this study. |
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- Choi, Y.-S., and C.-H. Ho, 2009, Validation of the cloud property retrievals from the MTSAT-1R imagery using MODIS observations, International Journal of Remote Sensing, 30(22), 5935-5985
[abstract]
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A cloud property retrieval algorithm optimized for five channels (centred at 0.6,
3.7, 6.7, 10.8, and 12.0 mm) has been explored for application to onboard meteorological
radiometers on geostationary satellites; however, its validity remains to be
established. Here, we present validation results for the cloud properties retrieved
by the developed algorithm from the full-disk imagery of the Multi-functional
Transport Satellite (MTSAT-1R) for August 2006. The considered cloud properties
include cloud phase (CP), cloud optical thickness (COT), effective radius (ER)
and cloud top pressure (CTP). Their one-month averages, daily variations, and
respective collocated values are compared with the Moderate Resolution Imaging
Spectroradiometer cloud data. Our validation results show that an additional
6.7 mm brightness temperature test in CP retrieval identifies water and ice phases
that may be overlooked in the 10.8- and 12.0-mm bands. Our method to extract
cloud-reflected radiances at the 0.6- and 3.7-mm bands contributes to the accuracy
of the COT for values between 5 and 60, and the ER for values less than 40 mm.
Estimating high-cloud top pressure from the radiance ratio in the 6.7- and 10.8-mm
bands remarkably reduces (by up to 70%) large uncertainties in the CTP, which
may be found in the presence of high thin cirrus clouds. |
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- Kim, B.-G., M.-H. Choi, and C.-H. Ho, 2009, Weekly periodicities of meteorological variables and their possible association with aerosols in Korea, Atmospheric Environment , 43, 6058-6065, doi:10.1016/j.atmosenv.2009.08.023
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- Lee, S., J.-G. Jhun, M. Kwon and W. Kim, 2008, Change in the Western North Pacific Summer Monsoon Circulation due to the CO2 Increase in IPCC AR4 CGCMs, Asia-Pacific Journal of Atmospheric Sciences, 44, 4, p. 351-368
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- Park, T.-W., J.-H. Jeong, C.-H. Ho, and S.-J. Kim, 2008, Characteristics of Atmospheric Circulation Associated with Cold Surge Occurrences in East Asia: A Case Study during 2005/06 Winter, Advances in Atmospheric Sciences, Vol. 25 No.5, 791 - 804
[abstract]
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The characteristics of the upper-level circulation and thermodynamical properties for the period when two distinct cold surges outbroke over East Asia during the 2005/06 winter are investigated. From early December 2005 to early January 2006 exceptionally cold weather lasted for approximately one month due to two successive cold surges took place on December 2, 2005 and January 2, 2006, respectively. This study reveals that both involve the upper-tropospheric circulation, which induces the amplification and expansion of the surface Siberian High toward East Asia but arose from different causes: the former is caused by the upper-level blocking originated from the North Pacific and the latter is caused by the upper-level wave train across the Eurasian Continent. In particular, it is suggested that the lower-tropospheric anomalous wind caused by upper-level circulation anomalies and steep meridional temperature gradient amplified by phase-locked annual cycle combined to induce very strong cold advection in East Asia, which results exceptional cold weather to last for several weeks. The present results emphasize that the characteristics of the upper-tropospheric circulation can be considered as important precursors to cold surge occurrences in East Asia. |
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- Sui, C.-H., X. Li, C.-H. Ho, and K.-M. Lau, 2008, Effects of radiative cooling on the tropical convective response to sea surface temperature: 2-D large domain cumulus ensemble simulations, Journal of Geophysical Research, 113, D08116, doi:10.1029/2007JD008557.
[abstract]
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The effects of radiative cooling on the tropical convective response to sea surface temperature (SST) are investigated using a series of two-dimensional large domain cloud-resolving simulations. The experiments are designed with an imposed warm-pool SST at 2.5°C, 3.5°C, and 4.5°C higher than the cold-pool SST, which is specified at 26°C. The area ratio of the model cold pool to the warm pool is set to 2.2. It is observed that the warm-pool convection intensifies when the SST difference between the warm and cold pools increases from 2.5°C to 3.5°C, whereas the warm-pool convection strength does not significantly change when the SST difference increases from 3.5°C to 4.5°C, which is qualitatively consistent with the observations. The analysis of the atmospheric heat budgets shows that the cap on the development of convection over the warm pool is due to a radiative cooling over the cold pool that has a small variability. The cloud-resolving model simulations indicate that the area of the radiatively driven subsidence expands to produce an enhanced mass exchange between the warm and cold pools in response to the enhanced SST difference between them. This acts against the tendency for increased clouds by the enhanced upward mass flux in response to the warmer SST over the warm pool; significantly stronger SST differences between the two pools (e.g., ≥ 3.5°C in the cloud-resolving model) do not proportionally produce further intensive convection activities over the warm pool. |
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- Jeong, J.-H., C.-H. Ho, Deliang Chen, and T.-W. Park, 2008, Land Surface Initialization Using an Offline CLM3 Simulation with the GSWP-2 Forcing Dataset and Its Impact on CAM3 Simulations of the Boreal Summer Climate , Journal of Hydrometeorology, Vol.9,1231-1248
[abstract]
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The impacts of initialized land surface conditions on the monthly prediction were investigated using ensemble simulations from the Community Atmosphere Model version 3 (CAM3). The land surface initialization was based on an offline calculation of Community Land Model version 3 driven by observation based meteorological forcings from the Global Soil Wetness Project 2 (GSWP2). A simple but effective correction method was applied to the GSWP2 forcings prior to the offline calculation to reduce the discrepancies between the observation-forced land surface conditions and the modeling system, which can cause climate drift and initial shock problems. The climatological mean of GSWP2 forcings was adjusted to that of the target model (CAM3), while the monthly anomalies were scaled to the model statistics and high-frequency synoptic variabilities were included.
Ensemble hindcast experiments with and without land surface initialization were conducted for the boreal summer (May–September), for 1983–95. The initialization process is shown to prevent climate drift and to transfer the atmospheric anomalies to the land surface memory. Statistical analyses of the simulation results reveal that the land surface initialization increased the externally forced variance over most continental regions, which is translated to enhanced potential predictability, particularly for regions with strong land–atmosphere coupling. |
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- Choi, Y.-S., C.-H. Ho, B.-G. Kim, and S.-K. Hur, 2008, Long-term variation in midweek/weekend cloudiness difference during summer in Korea, Atmospheric Environment, 42(28), 6726–6732
[abstract]
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A 58-year record (1950-2007) of cloudiness measured at 11 ground stations in South Korea revealed that summertime cloudiness for Wednesday through Friday versus that for Saturday through Monday exhibited a bell-shaped curve; the midweek/weekend difference increased up to 6% in the 1960s and early 1970s, and decreased in the mid and late 1970s. Since 1980, the anomaly has become as small as before 1960 (within ±2%). This bell-shaped interdecadal variation in midweek/weekend difference in cloudiness had a strong negative correlation with those in insolation and diurnal temperature range and a positive correlation with those in relative humidity and number of days with light rain (<5 mm day–1) from coincident ground measurements. Unlike the meteorological variables, the aerosol concentrations from the stations in the same cities appear to be consistently higher in the midweek than on the weekend in recent years (1990-2004). Therefore the long-term variations in midweek/weekend differences in cloudiness and relevant meteorological variables suggest that the regional weekly weather variations are unpredictable despite the rapid industrial growth in South Korea in the past few decades. This study discusses plausible interpretations related to aerosol effects. |
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- Ho, C.-H., M.-S. Park, Y.-S. Choi, and Yukari N. Takayabu , 2008, Relationship between intraseasonal oscillation and diurnal variation of summer rainfall over the South China Sea, Geophysical Research Letters, 35, L03701, doi:10.1029/2007GL031962.
[abstract]
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The diurnal variations in summer rainfall over the South China Sea (110°E−120°E, 10°N−20°N) are examined for active and inactive intraseasonal oscillation (ISO) periods that are characterized by strong and weak 850-hPa zonal winds, respectively. By analyzing the rainfall retrievals from the Tropical Rainfall Measuring Mission Precipitation Radar for the period 1999–2006, it is found that the peak rainfall during the active and inactive ISO periods occurs in the late morning and late evening, respectively. The morning peak in the active ISO period arises from the organized oceanic convective systems associated with the local convergence along the west coast of the Philippines. The evening peak in the inactive ISO period originates from a stratiform morphology that is initiated by land-based convective systems owing to the increased thermodynamic instability over the Philippines during daytime. |
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- Choi, Y.-S., C.-H. Ho, D. Chen, Y.-H. Noh, and C.-K. Song, 2008, Spectral analysis of weekly variation in PM10 mass concentration and environment conditions over China, Atmospheric Environment, 42(4), 655–666.
[abstract]
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This study investigates the region-dependent anthropogenic weekly variation in air pollutants and its relationship with
the meteorological conditions over China for the summers of 2001–2005. Spectral analysis was applied to the local daily
observations of PM10 (aerosol particulate matter with a diameter o10 mm) mass concentrations and precipitation from 31
ground stations, reanalysis estimates of regional atmospheric variables, and satellite retrievals of clouds. Our analysis
shows that the 6–8-day variance of PM10 concentrations from the periodogram is closely correlated with the mean PM10
concentration, which may depend on the size (population) and geographical setting of a city, its prevailing climatic
conditions, and the type/degree of human activities. We define normalized variance as the ratio of the 6–8 days to 2–14-day
variance of PM10 concentrations, possibly indicating the relative anthropogenic signal to the noise of natural weather
variability. The normalized variance of PM10 concentrations has a distinct regional rainfall distribution from that of the
mean PM10 concentration in China. As compared to regions with lower normalized variance of PM10 concentrations, the
regions with higher normalized variance generally show higher normalized variance of rainfall events, 1000 hPa wind
speeds, sea-level pressure, size spectrum and phase of cloud particles, cloud optical depth, and cloud top pressure. Our
results confirm the presence of the interaction between PM10 and the meteorological conditions in the boundary layer, and
suggest a possible link of cloud formation to PM10 on a weekly scale. |
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- Jeong, J.-H., B.-M. Kim, C.-H. Ho, and Y.-H. Noh, 2008, Systematic Variation in Wintertime Precipitation in East Asia by MJO-induced Extratropical Vertical Motion, Journal of Climate, 21(4), 788–801.
[abstract]
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The variations in the wintertime precipitation over East Asia and the related large-scale circulation associated with the Madden-Julian oscillation (MJO) are examined. By analyzing the observed daily precipitation for the period 1974-2000, it is found that the MJO significantly modulates the distribution of precipitation over four East Asian countries. Most of the MJO-precipitation relation is explained by the changes in the large-scale circulations due to the MJO, particularly those that involve moisture supply in the lower troposphere and vertical motion near an entrance region of the East Asian jet. A diagnostic approach using the generalized omega equation reveals that anomalous vertical motion has been primarily induced to balance the quasi-geostrophic motion when the MJO-related large-scale circulation encounters the Asia-Pacific jet. |
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- Kim, J.-H., C.-H. Ho, H.-S. Kim, C.-H. Sui, and S.-K. Park, 2008, Systematic variation of summertime tropical cyclone activity in the western North Pacific in relation to the Madden-Julian oscillation, Journal of Climate, 21(6), 1171-1191
[abstract]
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The variability of observed tropical cyclone (TC) activity (i.e., genesis, track, and landfall) in the western North Pacific (WNP) is examined in relation to the various categories of the Madden-ulian oscillation (MJO) during summer (June-eptember) for the period 1979-2004. The MJO categories are defined based on the empirical orthogonal function analysis of outgoing longwave radiation data.
The number of TCs increases when the MJO-related convection center is located in the WNP. The axis of preferable genesis region systematically shifts like a seesaw in response to changes in the large-scale environments associated with both the east- and northward propagation of the MJO and the intraseasonal variability of the WNP subtropical high. Further, we reveal that the density of TC tracks in each MJO category depends on the systematic shift in the main genesis regions at a first-order. Also, it is affected by the prevailing large-scale steering flows in each MJO category. When the MJO-related convection center is found in the equatorial Indian Ocean (the tropical WNP), a dense area of tracks migrates eastward (westward). The effect of extreme ENSO events and the variations occurring during ENSO neutral years are also examined.
A statistical analysis of TC landfalls by the MJO category is applied in seven selected subareas—the Philippines, Vietnam, South China, Taiwan, East China, Korea, and Japan. While a robust and significant modulation in the number of TC landfalls is observed in South China, Korea, and Japan, the modulation is marginal in the remaining four subareas.
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- Choi, Y.-S., C.-H. Ho, D.-Y. Gong, R. Park, and J. Kim, 2008, The impact of aerosols on the summer rainfall frequency in China, Journal of Applied Meteolorogy and Climatology, 47, 1802–1813
[abstract]
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The authors investigate the short-term relationship between aerosol concentrations and summer rainfall frequency in China using the daily surface observations of PM10 (particulate matters with a diameter of less than 10 m) mass concentration, rainfall, and satellite-observed cloud properties. Results in this study reveal that on the time scale of a few days, aerosol concentration is positively correlated with the frequency of moderate rainfall (1020 mm day1) days, but is negatively correlated with the frequency of light rainfall (< 5 mm day1) days. Satellite observations of cloud properties show that higher aerosol concentrations are positively correlated with the increase in mixed cloud amount, cloud effective radius, cloud optical depth, and cloud top heights; this corresponds to the decrease in low-level liquid clouds and the increase in mid-level ice/mixed clouds. Based on this analysis, the authors hypothesize that the increase in aerosol concentration results in the increase in summer rainfall frequency in China via enhanced ice nucleation in the mid-troposphere. However, over the past few decades, observations show an increasing long-term trend in aerosol concentration but decreasing trends in summer rainfall frequency and relative humidity (RH) in China. Despite the short-term positive relationship between summer rainfall frequency and aerosol concentration found in this study, the long-term variations in summer rainfall frequency in China are mainly determined by other factors including RH variation possibly caused by global and regional climate changes. A continuous decrease in RH resulting in less summer rainfall frequency may further enhance aerosol concentrations in the future in conjunction with the increase in the anthropogenic emissions. |
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- Choi, Y.-S., C.-H. Ho, M.-H. Ahn, and Y.-M. Kim, 2007, An exploratory study of cloud remote sensing capabilities of the Communication, Ocean and Meteorological Satellite (COMS) imagery, International Journal of Remote Sensing, 28, 4715-4732.
[abstract]
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The present study documents optimal methods for the retrieval of cloud
properties using five channels (0.6, 3.7, 6.7, 10.8 and 12.0 mm) that are used in
many geostationary meteorological satellite observations. Those channels are
also to be adopted for the Communication, Ocean and Meteorological Satellite
(COMS) scheduled to be launched in 2008. The cloud properties focused on are
cloud thermodynamic phase, cloud optical thickness, effective particle radius and
cloud-top properties with specific uncertainties. Discrete ordinate radiative
transfer models are simulated to build up the retrieval algorithm. The cloud
observations derived from the Moderate-resolution Imaging Spectroradiometer
(MODIS) are compared with the results to assess the validity of the algorithm.
The preliminary validation indicates that the additional use of a band at 6.7 mm
would be better in discriminating the cloud ice phase. Cloud optical thickness and
effective particle radius can also be produced up to, respectively, 64 and 32 mm by
functionally eliminating both ground-reflected and cloud- and ground-thermal
radiation components at 0.6 and 3.7 mm. Cloud-top temperature (pressure) in
¡3K (¡50 hPa) uncertainties can be estimated by a simple 10.8-mm method for
opaque clouds, and by an infrared ratioing method using 6.7 and 10.8 mm for
semitransparent clouds. |
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- Gong, D.-Y., S.-J. Kim, and C.-H. Ho, 2007, Arctic Oscillation and ice severity in the Bohai Sea, East Asia, International Journal of Climatology, 27, 1287-1302.
[abstract]
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http://www3.interscience.wiley.com/cgi-bin/abstract/114107196/ABSTRACT
The Bohai Sea is the southernmost sea in the Northern Hemisphere where seasonal freezing takes place in winter. Climate and ice conditions there are very sensitive to large-scale climatic variations. In the present study, the authors investigated the relationships of ice severity in the Bohai Sea to the planetary Arctic Oscillation (AO) during the period 1954/55-2001/02. It has been found that during low-AO winters the regional mean temperature around the Bohai Sea is evidently lower, and the number of freezing days, freezing degree days and the length of freezing duration all change significantly. Daily temperature distribution shows a significant difference in both mean and variance between high-AO and low-AO phases, and the changes in the temperature means dominate over that of the variance in the context of sea ice severity. The temperature-AO relation is well supported by the corresponding features of the large-scale atmospheric circulation system. AO-related changes in the Siberian High and East Asian Trough cause remarkable changes to the thermal conditions at the surface and to the dynamical conditions in the middle troposphere, consequently affecting the air temperature over the Bohai Sea and ice severity. The AO-sea ice severity relation has been generally stationary over time during the last one hundred years. Analysis of cross-power coherency between the AO and ice indices for the last century shows that the highest and significant covariance stands at periods of about 2.1, 3, and 7.5-14 years. The Bohai Sea ice severity has declined rapidly since the 1970s, which is unprecedented since 1880, and this feature is in agreement with the positively upward trend in the AO and the associated changes in the Siberian sea level pressure, East Asian Trough, and the regional temperature.
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- Park, M.-S., Y.-S. Choi, C.-H. Ho, C.-H. Sui, S.-K. Park, and M.-H. Ahn, 2007, Regional cloud characteristics over the tropical northwestern Pacific as revealed by Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar and TRMM Microwave Imager, Journal of Geophysical Research, 112, D05209, doi:10.1029/2006JD007437
[abstract]
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The present study investigates regional cloud characteristics over the tropical northwestern Pacific using Tropical Rainfall Measuring Mission (TRMM) data sets such as rain rate, radar reflectivity, and passive microwave radiometer polarization corrected temperature (PCT). In particular, the tropical northwestern Pacific is divided into two surface rain maxima regions: the South China Sea (SCS) and the Philippine Sea (PS). The TRMM variables are retrieved by a pair of spaceborne microwave sensors, Precipitation Radar (PR) and TRMM Microwave Imager (TMI). It is revealed that the SCS contains more frequent deeply developed convective systems relative to the PS on the basis of the analysis of the PR and TMI version-6 data during a 4-year period (1998-2001) of summers. This is mainly indicated by two factors: strong PR reflectivity (≥30 dBZ) above the freezing level (∼5 km) and TMI ice-scattering signature (PCT at 85.5 GHz ≤ ∼190 K, and PCT at 37.0 GHz ≤ ∼260 K), which are more frequent over the SCS than over the PS. Comparison of TMI and PR rain rates, a relatively small (large) positive PR-TMI bias is observed for an average of rainy areas over the SCS (PS). This region-dependent PR-TMI bias can arise from the regionally different extents of both (1) the PR's underestimate by attenuation correction and (2) the TMI's overestimate by emission from the melting layer (i.e., SCS > PS in (1) and (2)). These differences are due to the excess of heavy rainfall events, high rain rates, strong convective intensities, and high cloud top heights in the SCS compared with the PS. |
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- Gong, D.-Y., C.-H. Ho, D. Chen, Y. Qian, Y.-S. Choi, and J. Kim, 2007, Weekly cycle of aerosol-meteorology interaction over China, Journal of Geophysical Research, 112, D22202, doi:101029/2007JD008888.
[abstract]
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Weekly cycles of the concentration of anthropogenic aerosols have been observed in
many regions around the world. The phase and the magnitude of these cycles,
however, vary greatly depending on region and season. In the present study the authors
investigated important features of the weekly cycles of aerosol concentration and the
covariations in meteorological conditions in major urban regions over east China, one of
the most polluted areas in the world, in summertime during the period 2001–2005/2006.
The PM10 (aerosol particulate matters of diameter < 10 mm) concentrations at 29
monitoring stations show significant weekly cycles with the largest values around
midweek and smallest values in weekend. Accompanying the PM10 cycle, the
meteorological variables also show notable and consistent weekly cycles. The wind speed
in the lower troposphere is relatively small in the early part of the week and increases after
about Wednesday. At the same time, the air temperature anomalies in low levels are
positive and then become negative in the later part of the week. The authors hypothesize
that the changes in the atmospheric circulation may be triggered by the accumulation
of PM10 through diabatic heating of lower troposphere. During the early part of a week
the anthropogenic aerosols are gradually accumulated in the lower troposphere. Around
midweek, the accumulated aerosols could induce radiative heating, likely destabilizing the
middle to lower troposphere and generating anomalously vertical air motion and thus
resulting in stronger winds. The resulting circulation could promote ventilation to reduce
aerosol concentrations in the boundary layer during the later part of the week.
Corresponding to this cycle in anthropogenic aerosols the frequency of precipitation,
particularly the light rain events, tends to be suppressed around midweek days through
indirect aerosol effects. This is consistent with the observed anthropogenic weather cycles,
i.e., more (less) solar radiation near surface, higher (lower) maximum temperature, larger
(smaller) diurnal temperature range, and fewer (more) precipitation events in midweek
days (weekend). |
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- Ho, C.-H., E.-J. Lee, I. Lee, and S.-J. Jeong, 2006, Earlier spring in Seoul, Korea, International Journal of Climatology, Vol. 26 No.14, 2117 - 2127, doi:10.1002/joc.1356
[abstract]
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http://www3.interscience.wiley.com/cgi-bin/abstract/112633439/ABSTRACT
In the present study, long-term changes in the first bloom date of shrub and tree species in Seoul (126.56E 37.34N), Korea were examined using historical observational data for the period 1922-2004 (83 years). The study focused on two shrub species, golden-bell (Forsythia koreana) and azalea (Rhododendron mucronulatum), and three tree species, cherry (Prunus yedoensis), peach (Prunus persica), and American locust (Robinia pseudoacacia). The annual-mean temperature has increased by about 2 캜 in Seoul over the 83 years analyzed. The temperature increase is significant during the winter and early spring and becomes less significant during late spring. As a result of this regional warming, all five species showed an advance in the first bloom date over this time period. The advanced date is particularly apparent in early-spring flowering species like golden-bell (-2.4 days 10-year-1), azalea (-2.4 days 10-year-1), cherry (-1.4 days 10-year-1), and peach (-1.4 days 10-year-1) as compared to late-spring flowering species like American locust (-0.5 days 10-year-1).
The present results have demonstrated that the major factor for the determination of flower blooming is heat accumulation, i.e. a certain threshold of growing degree-days (GDD) index. In particular, early spring flowers were sensitive to the accumulation of warm temperature than late-spring flowers.
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- Kim, J.-H., C.-H. Ho, M.-H. Lee, J.-H. Jeong, and D. Chen, 2006, Large increase in heavy rainfall associated with tropical cyclone landfalls in Korea after the late 1970s., Geophysical Research Letters, 33, L18706, doi:10.1029/2006GL027430
[abstract]
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http://www.agu.org/pubs/crossref/2006/2006GL027430.shtml
This study presents a new demonstration of the abrupt increase in the heavy rainfall events (≥100 mm day-1) during August-September in Korea around the late 1970s. The accumulated heavy rainfall averaged for the two months over 12 stations was 57 mm during 1954-77 (ID1); however, it changed to 103 mm during 1978-2005 (ID2). This change is found to be associated with landfalling tropical cyclones (TCs). The most plausible mechanism that accounts for the TC-heavy rainfall relationship is an enhanced TC-upper-tropospheric trough (UTT) interaction, which results from a southward shift of the upper-tropospheric jet in East Asia during ID2. While the intensity and duration of the landfalling TCs in Korea does not appear to exhibit such an interdecadal change based on the data available, the enhanced TC-UTT interaction increases the upper(lower)-tropospheric divergence (convergence) and coherent ascending motion, which strengthen the frontal zone around Korea. |
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- Choi, Y.-S., and C.-H. Ho, 2006, Radiative effect of cirrus with different optical properties over the tropics in MODIS and CERES observations, Geophysical Research Letters, 33, L21811,doi:10.1029/2006GL027403, Editor's Highlight
[abstract]
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http://www.agu.org/pubs/crossref/2006/2006GL027403.shtml |
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- Lee Y.-K., B.-K. Moon, M. Kwon, and J.-G. Jhun, 2006, Roles of wind stress variation in the western North Pacific on the decadal change of ENSO, Journal of Korean Earth Science Society, 27(6), 657-694
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- Jeong, J.-H. , B.-M. Kim, C.-H. Ho, G.-H. Lim, Deliang Chen, 2006, Stratospheric origin of cold surge occurrence in East Asia, Geophysical Research Letter, 33, L14710, doi:10.1029/2006GL026607
[abstract]
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http://www.agu.org/pubs/crossref/2006/2006GL026607.shtml
In the present study, we have found a precursory signal in the stratospheric circulation prior to the cold surge occurrence in East Asia. Over northern Eurasia, about one week before the cold surge occurrence, strong stratospheric negative potential vorticity anomalies and rising of geopotential height are observed. The dynamic linkage between the stratospheric perturbations and the tropospheric adjustment, along with initial disturbances for a cold surge occurrence, are discussed. |
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- Yoo, S.-H., S. Yang, and C.-H. Ho, 2006, Variability of the Indian Ocean sea surface temperature and its impacts on Asian-Australian monsoon climate, Journal of Geophysical Research, 111, D03108
[abstract]
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http://www.agu.org/pubs/crossref/2006/2005JD006001.shtml
In this study, the authors investigate the relationships between the Indian Ocean (IO) sea surface temperature (SST) and the Asian-Australian monsoon (AAM) on seasonal to interannual timescales. They focus on the dominant features of IO SST, the impacts of IO SST on different monsoon components, and the relative importance of the northern and southern IO for the AAM. The dominant mode of IO SST is often characterized by uniform warming or cooling, with maximum variance in the Southern Hemisphere. This mode exerts a larger impact on monsoon variability than does the tropical IO dipole. The IO SST is strongly persistent from the boreal fall to the next spring even summer and less persistent from boreal summer to fall, a feature related to seasonal alternation of the dominance of the impacts of Pacific and IO SSTs on the Asian-Australian monsoons. While the tropical central Pacific SST exerts an apparently larger impact on the monsoon climate in the boreal winter and the transitional seasons, the IO SST affects the summer regional climate more strongly. The springtime IO SST leads to opposite changes in the south Asian monsoon (SAM) and the Southeast Asian monsoon (SEAM), reinforcing the out-of-phase relationship that appears often between the two monsoon components. While a warmer IO strengthens the SAM, it weakens the SEAM. Furthermore, the southern IO SST is related to the Asian summer monsoon more closely than the northern IO SST. The boreal fall IO SST, especially that in the north IO, is strongly associated with the subsequent Australian summer monsoon. |
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- Ho, C.-H., J.-H. Kim, J.-H. Jeong, H.-S. Kim, and D. Chen, 2006, Variation of tropical cyclone activity in the South Indian Ocean: El Niño–Southern Oscillation and Madden-Julian Oscillation effects, Journal of Geophysical Research , 111, D22101, doi:10.1029/2006JD007289
[abstract]
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http://www.agu.org/pubs/crossref/2006/2005JD006001.shtml
The present study examines variation of tropical cyclone (TC) activity in the South Indian Ocean (SIO) during TC seasons (December–March) for the period 1979–2004. The impact of the El Niño–Southern Oscillation and the Madden-Julian Oscillation (MJO) on the variation is revealed through a composite analysis. During El Niño periods TC genesis was shifted westward, enhancing the formation west of 75°E and reducing it east of 75°E. These changes in the genesis correspond to a westward shift of convection. It may be explained by a remote effect on the SIO; that is, the increase in sea surface temperature in the central eastern Pacific alters the Walker circulation and forms an anomalous anticyclonic circulation in the east SIO during El Niño. The spatial difference in TC passages between El Niño and La Niña shows a significant decrease to the southeast of Madagascar but a moderate increase in the central midlatitude SIO, indicating that TCs move farther east during El Niño. This change is possibly due to the anomalous southwesterlies east of Madagascar. Variation of TC activity also depends on various MJO phases: frequent TC passages for phases 2–4 (strong convective activity straddles along the equatorial Indian Ocean) versus infrequent TC passages for other phases. TC tracks tend to be more south oriented in phase 3 compared with those in phases 2 and 4. This is possibly caused by the increased steering northerlies which are a part of the anticyclonic Rossby wave of Gill type in response to the suppressed MJO-related convection in the maritime continent. |
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- Gong, D.-Y., G. Dong, and C.-H. Ho, 2006, Weekend effect in diurnal temperature range in China: Opposite signals between winter and summer, Journal of Geophysical Research, 111, D18113, doi:10.1029/2006JD007068
[abstract]
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Intense human activity can impact weather and climate in many ways. One possible important consequence is the weekly cycle (so-called weekend effect) in the diurnal temperature range (DTR). The weekend effect is defined as the average DTR for Saturday through Monday minus the average DTR for Wednesday through Friday. In the present study, the weekend effect in the DTR over east China combined with station observations of maximum and minimum temperatures, relative humidity, and total solar irradiance for the period 1955–2000 was analyzed. Results show that the weekend effect in the DTR has the opposite signal between winter (December, January, and February) and summer (June, July, and August). Wintertime DTR tends to have a positive weekend effect (i.e., larger DTR in weekend days compared to weekdays), in association with increased maximum temperature and total irradiance but decreased relative humidity. While summertime DTR displays a much stronger and significantly negative weekend effect (i.e., smaller DTR in weekend days), in association with decreased maximum temperature and total solar irradiance but increased relative humidity and a greater number of rainy days. This study indicates that the DTR difference between weekend and weekdays is predominantly related to weekly changes in the maximum temperature. The weekend effect in the DTR and maximum temperature is also found in the Reanalysis 2 data. The weekend effect in winter is supported by an analogous holiday (Spring Festival) effect. Since the late 1970s, the weekend effect has been enhanced in both winter and summer, concurrent with rapid development and enhanced human activity in China. The direct and indirect effects of human-related aerosols on radiation, cloud, precipitation, and so on, might play an important role in generating the opposite signal in the weekend effect for different seasons. During a dry winter, the reduction of aerosol concentrations may overwhelmingly impact on the DTR through a direct effect, i.e., by increasing total solar irradiance near the surface and raising the daytime temperature and maximum temperature and lowering relative humidity. By contrast, in summer the indirect effect of aerosols, i.e., reduction in precipitation efficiency caused by more numerous and smaller cloud droplets, would largely be responsible for the increased numbers of rainy days, the reduction of the total solar irradiance, and the lowering of the maximum temperature and DTR. |
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- Jeong, J.-H., and C.-H. Ho, 2005, Changes in occurrence of cold surges over East Asia in association with Arctic Oscillation, Geophysical Research Letters, Vol. 32, L14704, doi:10.1029/2005GL023024
[abstract]
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It has been newly found that the occurrence of cold surges in east Asia is significantly influenced by the Arctic Oscillation (AO). In the present study, the events of cold surge are objectively determined based on several synoptic criteria and the phase-dependency of its occurrences in association with the AO has been revealed. During the negative AO phase, the frequency of cold surge occurrence is relatively increased than that of neutral and positive AO phases. The variation of upper level trough and jet stream over east Asia and the Siberian High in association of AO are suggested to explain the change of cold surge occurrences. |
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- Kim, J.-H. and C.-H. Ho, C.-H. Sui,, 2005, Circulation features associated with the record-breaking typhoon landfall on Japan in 2004, Geophysical Research Letters, Vol. 32, L14713, doi:10.1029/2005GL022494
[abstract]
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Ten typhoons struck Japan in 2004, which was an all-time high although the total number of typhoons formed over the western North Pacific was slightly above normal. The characteristics of typhoon activity are the unusually high number of typhoons approaching Japan in the early summer (June) and fall (September and October) and the frequent landfalls in the middle summer (July and August). Seasonal mean large-scale circulation in 2004 was characterized by a split of the North Pacific subtropical high (NPSH) east of Taiwan and persistent anticyclonic anomalies to the southeast of Japan, enabling typhoons to penetrate the weakened NPSH and move to Japan. Two possible causes are suggested here to maintain the persistent anticyclonic anomalies near Japan: one is positive feedback between typhoons moving northward and midlatitude circulation near Japan, the other is response to the broad-scale tropical deep convection. A further modeling study is required to substantiate these arguments. |
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- Choi, Y.-S., C.-H. Ho, and C.-H. Sui, 2005, Different Optical Properties of High Cloud in GMS and MODIS Observations, Geophysical Research Letters, 32, L23823, doi:10.1029/2005GL024616
[abstract]
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The optical properties of high cloud are compared between two satellite retrievals taken from the Geostationary Meteorological Satellite-5 (GMS) and the Moderate-resolution Imaging Spectroradiometer (MODIS) in the tropical western Pacific (TWP) for the years 1998~2001. The MODIS high-cloud amount determined by 1.38-μm reflectances (>1.1%) is approximately twice that of GMS determined by 11-μm brightness temperatures (<260 K). The optical depths associated with the retrieved high clouds are calculated using a radiative transfer model. The minimum detectable value of optical depths by the MODIS and GMS measurements is around 0.1 and 2.0, respectively. Variations of MODIS and GMS high clouds with respect to the mean sea surface temperatures (SSTs) in the TWP are examined next. There exist large discrepancies in the change rates in high clouds with increasing SST between GMS and MODIS in the available data for the years 2000 and 2001. |
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- Kim, J.-H., C.-H. Ho, C.-H. Sui, and S.-K. Park, 2005, Dipole structure of interannual variations in summertime tropical cyclone activity over East Asia., Journal of Climate, Vol. 18, No. 24, 5344–5356
[abstract]
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The present study examines variations in summertime (July~September) tropical cyclone (TC) activity over East Asia during the period 1951~2003. To represent TC activity, a total of 853 TC best tracks for the period were converted to TC passage frequencies (TPFs) within 5° × 5° latitude~longitude grids; TPFs are defined as the percentage values obtained by dividing the number of TC appearances in each grid box by the total number of TCs each year. Empirical orthogonal function analysis of the TPF showed three leading modes: two tropical modes that represent the long-term trend and the relationship with ENSO and one midlatitude mode that oscillates between south of Korea and southeast of Japan with an interannual time scale. The latter proved to be the most remarkable climatic fluctuation of summertime TC activity in the midlatitudes and is referred to as the East Asian dipole pattern (EADP) in this paper.
Anomalous atmospheric flows directly connected to the EADP are an enhanced anticyclonic (cyclonic) circulation centering around Japan when the TPF is high south of Korea (southeast of Japan), thereby showing an equivalent barotropic structure in the entire troposphere. This regional circulation anomaly varies in conjunction with the zonally oriented quasi-stationary Rossby wave train in the upper troposphere. This wave train is meridionally trapped in the vicinity of the summer-mean jet stream; therefore, the mean jet stream alters its internal meandering structure according to the phase of the wave train.
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- Choi, Y.-S., C.-H. Ho, M.-H. Ahn, and Y.-S. Kim, 2005, Enhancement of the consistency of MODIS thin cirrus with cloud phase by adding 1.6-㎛ reflectance, International Journal of Remote Sensing, Vol. 26, No. 21, 4669 - 4680, doi: 10.1080/01431160500239305
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- Jeong, J.-H., C.-H. Ho, B.-M. Kim, and W.-T. Kwon, 2005, Influence of the Madden-Julian Oscillation on wintertime surface air temperature and cold surges in East Asia., Journal of Geophysical Research, Vol. 110, D11104, doi:10.1029/2004JD005408
[abstract]
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The variations of wintertime surface air temperature (SAT) and the occurrences of cold surges over east Asia in association with the Madden and Julian Oscillation (MJO) are examined. The MJO is defined as a combination of the two leading empirical orthogonal function modes of 850 and 200 hPa zonal winds and outgoing longwave radiation in the tropics. The spatial pattern and magnitude of SAT anomalies over east Asia significantly change with respect to MJO phases. Composite analysis reveals that the MJO-SAT relationship is mainly affected by strong temperature advection in the lower troposphere. In addition, occurrences of cold surges are identified using objectively determined synoptic criteria, and their relation to the MJO is analyzed. Most extreme cold surges occur when the MJO convection center is located over the Indian Ocean, and it is suggested that MJO-induced circulation anomalies may reinforce the amplification of normal cold surges to extreme cold surges. |
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- Ho, C.-H. , J.-H. Kim, Y.-B. Lee, K.-M. Lau, K.-M. Kim, and D.-Y. Gong, 2005, Interdecadal changes in heavy rainfall in China during the northern summer, The Journal of Terrestrial, Atmospheric and Oceanic Sciences, Vol.16 Num.5
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- Ho, C.-H. , J.-H. Kim, H.-S. Kim, C.-H. Sui, and D.-Y. Gong, 2005, Possible Influence of the Antarctic Oscillation on Tropical Cyclone Activity in the Western North Pacific, Journal of Geophysical Research, Vol. 110, No. D19, D19104, doi:10.1029/2005JD005766
[abstract]
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The present study investigates how large-scale atmospheric circulation in the Southern Hemisphere (SH) modulates tropical cyclone (TC) activity in the western North Pacific (WNP) during a typhoon season (July, August, and September; boreal summer). The variation of the SH circulation of interest is the Antarctic Oscillation (AAO). In the positive phase of AAO relative to its negative phase, two anomalous highs develop over the western Pacific in both hemispheres: a huge anticyclone in southeastern Australia and a relatively weak anticyclone in the East China Sea. These teleconnection patterns are examined and compared with previous analyses. Related to the AAO variations, a statistically significant alteration of TC activities is found over the WNP. The difference in the mean TC passage numbers over the East China Sea (120°~140°E, 20°~40°N) between the eight highest-AAO years and the eight lowest-AAO years is as large as 2, equivalent to a 50~100% increase from the climatology. This change is primarily a result of more TCs forming over the eastern Philippine Sea. On the other hand, TC passage numbers slightly decrease over the South China Sea. These changes in TC activity are predominant in August and are consistent with changes in low-level vorticity over the subtropical WNP. The influence of SH circulation variability on large-scale environments and tropical convection in the subtropical NH suggest a possible usage of AAO variation for long-range forecasting of TC activity over the WNP. |
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- Hee-Jun Song, Sung-Hoe Huh, Seon Kim Park, Joo-Hong Kim, and Chang-Hoi Ho, 2005, Typhoon track prediction by support vector machine using data reduction methods, Lecture Notes in Computer Science, 3081
[abstract]
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http://www.springerlink.com/content/31560g0908154423/ |
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- Yoo, S.-H., C.-H. Ho, S. Yang, H.-J. Choi and J.-G. Jhun, 2004, Influences of tropical-western and extratropical Pacific sea surface temperatures on the east and Southeast Asian climate in the summers of 1993-94., Journal of Climate, 17(13), 2673–2687
[abstract]
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This study emphasizes the importance of sea surface temperature (SST) over the tropical western Pacific and the ocean~atmosphere coupling in the extratropical Pacific for the climate in East and Southeast Asia. Specifically, it demonstrates that the anomalies of tropical SST explain many features of the climate variability in those regions during the summers of 1993 and 1994.
Very different atmospheric circulation patterns appeared in East and Southeast Asia between 1993 and 1994. Many regions including northern China, Korea, and Japan suffered from extremely high temperatures and severe droughts in the summer of 1994 but experienced reverse climate anomalies in the summer of 1993. To the south of these regions, the opposite climate patterns occurred. These climate features do not really resemble those associated with the El Nino~Southern Oscillation, which usually exerts a moderate impact on the East Asian climate. However, different SST anomalies have been observed in the tropical western and extratropical Pacific in the spring and summer between these two years. The authors carried out a series of simulations using an atmospheric circulation model and a slab oceanic model to understand the influences of these SST anomalies on the climate features.
Both the uncoupled atmospheric and coupled oceanic~atmospheric experiments indicate that the tropical western Pacific SST affects the East and Southeast Asia climate significantly. Warming in the tropical western Pacific produces hot, dry conditions in northern China, Korea, and Japan, and opposite climate signals to their south. These climate anomalies produced by the local SST resemble the observed climate difference between the summers of 1994 and 1993 when positive and negative SST anomalies, respectively, existed in the tropical western Pacific.
The coupled experiment also shows that the changes in extratropical atmospheric circulation caused by tropical SST anomalies generate changes in the extratropical Pacific SST, which, in turn, reinforces the climate signals produced by the tropical SST.
On the other hand, the uncoupled experiments forced by the extratropical Pacific SST anomalies show that the extratropical SST exerts an insignificant impact on the East and Southeast Asian climate. The change in this SST between 1994 and 1993 generates unrealistic climate patterns in some East Asian regions, accompanying an unnatural shift of the atmospheric circulation. |
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- Ho, C.-H. , J.-J. Baik, J.-H. Kim, D.-Y. Gong, and C.-H. Sui, 2004, Interdecadal changes in summertime typhoon tracks., Journal of Climate, 17(9), 1767-1776
[abstract]
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The present work examines interdecadal variations of typhoon tracks in the western North Pacific (WNP) during the boreal summer (June~September) for the period 1951~2001. Typhoon tracks are expressed as percentage values of the total number of typhoon passages into a 5° × 5° latitude~longitude grid box with respect to the total number of typhoons formed in the WNP. The analysis period is divided into two interdecadal periods: ID1 (1951~79) and ID2 (1980~2001). From ID1 to ID2, typhoon passage frequency decreased significantly in the East China Sea and Philippine Sea, but increased slightly in the South China Sea. The time series of typhoon passage frequency over the East China Sea and South China Sea further reveal a regime shift in the late 1970s, while those over the Philippine Sea indicate a continuous downward trend of −9% decade−1.
The interdecadal changes in typhoon tracks are associated with the westward expansion of the subtropical northwestern Pacific high (SNPH) in the late 1970s. The expansion of the SNPH to the southeast coast of Asia may result in a larger elliptic pathway of typhoon migration. This is consistent with the westward shift of the typhoon tracks from ID1 to ID2, resulting in an increase of typhoon passage frequency in the South China Sea and a decrease in the East China Sea. The change of typhoon tracks is partly due to the westward shift of major typhoon formation regions associated with a warmer sea surface temperature in the South China Sea. The decreasing typhoon passage frequency over the Philippine Sea is due to less typhoon formation in recent decades. This is consistent with the decreasing cyclonic relative vorticity in the lower troposphere. |
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- Gong, D.-Y., and C.-H. Ho, 2004, Intra-seasonal variability of wintertime temperature over East Asia, International Journal of Climatology, 24, 131-144
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There has been a profound warming over East Asia during the winter months (November through to March) over the past few decades. The goal of this study is to address the question of whether the daily temperature has become more variable in conjunction with this warming by using observed temperature data obtained from 155 Chinese and Korean stations. Prior to the analysis, the annual cycle is removed to obtain daily temperature anomalies for each winter for each station. Results show that the intra-seasonal variance generally decreases, implying that the daily temperatures are becoming less variable. Considering all stations as a whole, the rate of change is -0.49캜2 per decade (equivalent to -3.59% per decade). The changes are more robust in the northeastern portion of China. In contrast, there are no dominant trends for the skewness coefficients, except for clear negatively skewed trends in northeastern China. These results are consistent with an increase in the number of extremely cold events. Over the region, the frequency of low-temperature extremes (as low as below minus two standard deviations) increases at a rate of change of 0.26 days per decade, significant at the 95% confidence level. Both the Siberian high and Arctic oscillation (AO) exert a notable influence on the temperature variance. Intra-seasonal variance of the Siberian high and AO are significantly correlated with the temperature variance, whereas the seasonal mean state of the AO affects the temperature variance by modulating the high-frequency components of the Siberian high. The intra-seasonal variance of the Siberian high tends to decline at a rate of change of -10.7% per decade, significant at the 99% level; meanwhile, the mean wintertime AOs have strengthened in the last few decades. These two climate features together make a considerable contribution to the changes in intra-seasonal temperature variance in East Asia. |
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- Yang, S., K.-M. Lau, S.-H. Yoo, J. L. Kinter, K. Miyakoda, and C.-H. Ho, 2004, Upstream subtropical signals preceding the Asian summer monsoon circulation., Journal of Climate, 17(21), 4213-4229
[abstract]
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In this study, the authors address several issues with respect to the antecedent signals of the large-scale Asian summer monsoon that were earlier identified by Webster and Yang. In particular, they revisit the changes in the subtropical upper-tropospheric westerlies preceding the monsoon, depict the detailed structure of the monsoon's antecedent signals, and investigate the physical processes from the signals to the monsoon. They also explore the teleconnection of these signals to various large-scale climate phenomena and emphasize the importance of the upstream location of the signals relative to the Tibetan Plateau and the monsoon.
Before a strong (weak) Asian summer monsoon, the 200-mb westerlies over subtropical Asia are weak (strong) during the previous winter and spring. A significant feature of these signals is represented by the variability of the Middle East jet stream whose changes are linked to the Arctic Oscillation, North Atlantic Oscillation, El Nino~Southern Oscillation, and other climate phenomena. When this jet stream intensifies and shifts southeastward, cold air intrudes frequently from eastern Europe into the Middle East and southwestern Asia. As a result, in subtropical Asia, snow and precipitation increase, the ground wetness increases, and surface temperature decreases. A strengthening Middle East jet stream is also accompanied by increases in both stationary wave activity flux and higher-frequency eddy activities. The Tibetan Plateau acts to block these westerly activities propagating eastward and increase the persistence of the low-temperature anomalies, which in turn prolongs the atmospheric signals from winter to spring.
A strong link is found between the persistent low-temperature anomalies and the decrease in geopotential height over southern Asia, including the Tibetan Plateau, in spring. The latter indicates a late establishment of the South Asian high, and implies a delay in the atmospheric transition from winter to summer conditions and in the development of the summer monsoon. The preceding scenario for a strong Middle East jet stream and a weaker Asian monsoon can be applied accordingly for the discussion of the physical processes from a weak jet stream to a strong monsoon.
The current results of the relationship between the extratropical process and Asian monsoon resemble several features of the tropical~extratropical interaction mechanism for the tropospheric biennial oscillation (TBO). While the role of tropical heating is emphasized in the TBO mechanism, compared to the variability of the sea surface temperature related to El Nino~Southern Oscillation, the extratropical process examined in this study is more strongly linked to the Asian summer monsoon.
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- Gong, D.-Y., and C.-H. Ho, 2003, Arctic Oscillation signals in the East Asian summer monsoon, Journal of Geophysical Research, 108(D2), 4066, doi:10.1029/2002JD002193
[abstract]
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The present study examines the relationship between the Arctic Oscillation (AO) and the East Asian summer monsoon. Two rainfall data sets are used. One is obtained from 10 stations along the Yangtze River to the southern Japan and the other from gridded global land rainfall data for the period 1900~1998. All data are high-pass filtered before analyzing to highlight the interannual variability. Results show that the AO significantly influences on year-to-year variations in the East Asian summer monsoon rainfall. When AO leads by one month, the correlation between May~July AO and summer total rainfall is −0.44. When AO leads by two months, correlation becomes −0.32. Of all monthly, May AO shows the strongest connection to the summer monsoon rainfall. Correlation coefficient between them is −0.45. The large-scale atmospheric circulation patterns in East Asia in association with the AO are also evident. A positive phase of the AO in late spring is found to lead to a northward shift in the summertime upper tropospheric jet stream over East Asia. This northward shift of the jet stream is closely related to anomalous sinking motion in 20°~40°N and rising motion in surrounding regions. These changes give rise to a drier condition over the region extending from the Yangtze River valley to the southern Japan and a wetter condition in the southern China. Possible mechanisms connecting the late spring AO and summer monsoon rainfall are suggested. |
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- Ho, C.-H. , J.-Y. Lee, M.-H Ahn, and H.-S. Lee, 2003, A sudden change in summer rainfall characteristics in Korea during the late-1970s, International Journal of Climatology, 23, 117-128
[abstract]
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We have examined long-term climate change in Korea by studying daily rainfall data over a period of 48 years (1954-2001). The results show that there is a more frequent heavy rainfall anomaly larger than 100 mm per 3 months in recent years. For further investigation, we divide the whole period into two 24 year intervals, 1954-77 and 1978-2001. Two well-defined rainfall peaks occur during summertime in both intervals. During the earlier interval, primary and secondary rainfall peaks are found in early July and early September, respectively. In the later interval, on the other hand, the secondary peak is found in mid-late August, mainly attributed to enhanced heavy rainfall (30 mm day-1) events. Although a similar shift occurs in the primary peak, it is much smaller. Thus, the relatively dry spell between the two peaks becomes shorter in the later interval compared with the earlier one.
The domain-mean geopotential height at 700 hPa (700) over mid-latitude Asia (30-50?N, 60-120?E) for the summer also experienced a sudden increase in the mid 1970s. A comparison of the spatial distribution of 700 between the two intervals shows large positive differences over the central-eastern Asian continent in the later interval. In contrast to the positive anomaly of 700 in the later interval, there is a decreasing trend in surface temperature. The increased 700 introduces a stronger northerly wind over East Asia and possibly produces a moisture convergence, enhanced convective activity, and heavy rainfall over the region, in particular over Korea and central China. Copyright ⓒ 2003 Royal Meteorological Society.
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- Gong, D.-Y., and C.-H. Ho, 2003, Detection of large-scale climate signals in spring vegetation index (normalized difference vegetation index) over the Northern Hemisphere., Journal of Geophysical Research, 108(D16), 4498, doi:10.1029/2002JD002300
[abstract]
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Climate is one of the determinants driving ecosystems on both local and global scales. During the last two decades, there has occurred a dramatic temperature increase in the northern midlatitudes to high latitudes. The rapid warming has resulted in the promotion of bioactivity and an early growing season. However, the temperature and vegetation changes are not uniform in geographical distribution. In the present study, we analyze the spatial features in the normalized difference vegetation index (NDVI)-temperature relationship over Eurasia and North America in spring for the period 1982~2000. The NDVI data are derived from the Earth Observing System Pathfinder advanced very high resolution radiometer data sets. A singular value decomposition analysis is applied to the covariance matrix of the NDVI and temperature. Most of the squared covariance, 91.6%, is captured by the first seven paired modes. The result clearly indicates that the temperature is a focal factor influencing vegetation activity. Furthermore, those seven paired modes show large-scale features and well-defined patterns. The atmospheric circulation systems, such as the Southern Oscillation, North Atlantic Oscillation/Arctic Oscillation, Pacific/North American pattern, Eurasian pattern, western Pacific pattern, western Atlantic pattern, eastern Atlantic pattern, and North Pacific index, are found to be associated with that. The time coefficient corresponding to the first paired modes, centered on western Siberia, is correlated significantly with the Eurasian teleconnection pattern. Their correlation coefficients are 0.72 and 0.78 for vegetation and temperature, respectively, for the data period. Other modes are also correlated with one or more circulation indices. This implies that the large-scale circulation is essential for understanding the regional response of vegetation to global climate change. Taking all nine circulation indices and time lags into account, a large portion (71%) of the satellite-sensed variance in NDVI could be explained. The temperature-NDVI relationships did not change significantly when the NDVI was rescaled from 1 to 5 degrees, indicating that the singular value decomposition analysis is an appropriate technique for detecting the degree of coupling between vegetation and climate and that the vegetation-temperature relationship presented in this study is robust. |
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- Ho, C.-H. , M.-D. Chou, and C.-H. Sui, 2002, Comparison of different radiation budget data sets over tropical oceans, International Journal of Climatology, 22, 263-270
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We compare radiation budgets derived from different Earth Radiation Budget Experiment (ERBE) archives over the tropical oceans (30S and 30N) from 1985 to 1989. Two ERBE data sets are used. One is taken from the Earth Radiation Budget Satellite (ERBS), and the other from the combined ERBS, National Oceanic and Atmospheric Administration (NOAA) 9, and NOAA 10 satellites. The domain-mean all-sky outgoing longwave radiation (OLR) derived from the combined data set shows a notable change in early 1987 when NOAA 10 replaced NOAA 9. This change is also found in longwave (LW) cloud radiative forcing (CRF), all-sky shortwave (SW) radiation, and SWCRF. The ERBS, however, does not show such changes.
We also examine the sensitivity of cloud-radiation interaction to the sea surface temperature (SST) of the tropical oceans. In general, each component of radiative feedbacks derived from the two ERBE data have the same sign, although they show a certain degree of discrepancy in the magnitude. The discrepancy is more notable for averaged quantities over the entire tropical oceans, particularly over the subtropics where convective activities are relatively weak. The combined data show a larger sensitivity of LWCRF and SWCRF to SST than those of the ERBS, consistent with the above results. The response of clouds to an increase in SST has a net cooling effect when using the combined data but has a net heating effect when using the ERBS data (-0.80 W m-2 K-1 versus 0.48 W m-2 K-1). Most of the discrepancies of the net CRF between the two ERBE data sets can be accounted for by the difference in the sensitivity of all-sky OLR (4.52 W m-2 K-1 versus 1.73 W m-2 K-1). Copyright ⓒ 2002 Royal Meteorological Society.
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- Gong, D.-Y., and C.-H. Ho, 2002, Shift in the summer rainfall over the Yangtze River valley in the late 1970s, Geophysical Research Letters, 29(10), doi:10.1029/2001GL014523
[abstract]
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The summer rainfall over the middle-lower valley of the Yangtze River and over the whole eastern China experienced a notable regime shift in about 1979. This change is consistent with a simultaneous jump-like change in the 500 hPa geopotential height (Φ500) over the northern Pacific. The rainfall over the Yangtze River valley is closely related to the Φ500 averaged over the area 20°~25°N, 125°~140°E, with a correlation coefficient of 0.66 for the period 1958~1999. Since 1980, the subtropical northwestern Pacific high (SNPH) has enlarged, intensified, and extended southwestward. The changes in the SNPH are strongly associated with the variations of the sea surface temperatures (SSTs) of the eastern tropical Pacific and tropical Indian Ocean. The anomalies of these SSTs, responsible primarily for the shift of the summer rainfall over the Yangtze River through the changes in SNPH, precede the Φ500 signals with different leading times. |
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- Gong, D.-Y., and C.-H. Ho, 2002, Siberian high and climate change over middle to high latitude Asia, Theoretical and Applied Climatology, 72, 1-9
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- Lim, H.-S., and C.-H. Ho, 2000, Comparison of observed precipitation of GPCP with assimilated precipitation from ECMWF, NCEP/NCAR, and NASA/GEOS-1 reanalyses, Journal of the Meteorological Society of Japan, 78, 661-672
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- Kang, I.-S., C.-H. Ho, Y.-K. Lim, and K.-M. Lau, 1999, Principal modes of climatological seasonal and intraseasonal variations of the Asian summer monsoon, Monthly Weather Review, 127, 322-340
[abstract]
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Principal modes of climatological variation of the Asian summer monsoon are investigated. Data used in this study include the high cloud fraction produced by the International Satellite Cloud Climatology Project and sea level pressure, and 850- and 200-mb geopotential heights from ECMWF analysis for the five summers of 1985~89. It is shown that the seasonal evolution of the Asian summer monsoon is adequately described by a few leading EOFs. These EOFs capture the variations of regional rainbands over the East Asian and Indian regions.
The first mode is characterized by an increase in large-scale cloud over India and the subtropical western Pacific until mid-August. The second mode depicts large-scale cloud variations associated with the East Asian rainband referred to as Mei Yu and Baiu. This mode is associated with the development of summer monsoon circulation: a low pressure system over the Asian continent and a subtropical high over the Pacific. The third eigenmode is characterized by zonal cloud bands from northern India, crossing the Korean peninsula to Japan, and dryness over the oceans in the south of cloud bands. This mode is related to the mature phase of Changma rainy season in Korea associated with the northward movement of cloud bands and circulation systems from the subtropical western Pacific. This mode appears as a first principal mode of climatological intraseasonal oscillation (CISO) over the entire Asian monsoon region. The CISO mode has a timescale of about 2 months.
The northward moving CISO also appears in the 850- and 200-mb geopotential height fields as a first mode of each dataset. Based on the height variations of the CISO mode, it is suggested that the extratropical CISO during summer is related to a regional index cycle associated with the variation of north~south temperature gradient in East Asia.
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- Lau, K.-M., C.-H. Ho, and I.-S. Kang, 1998, Anomalous atmospheric hydrologic processes associated with ENSO: Mechanisms of hydrologic cycle-radiation interaction, Journal of Climate, 11, 800-815
[abstract]
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Using reanalysis data from the Goddard Earth Observing System (GEOS) Data Assimilation System, the authors have documented the basic three-dimensional features of anomalous atmospheric hydrologic processes observed during the El Nino~Southern Oscillation (ENSO). The most dominant anomaly pattern features a pair of subtropical temperature maxima straddling the equator in the upper troposphere coupled to a corresponding pair of temperature minima in the lower stratosphere in the form of a dipole. Over the Tropics and subtropics, the water vapor content is increased in regions of large-scale ascent with maximum response in the middle troposphere, whereas substantial drying is found in the descending branches of the Walker and Hadley circulations. While the temperature and moisture patterns in the lower troposphere are thermodynamically linked to the sea surface temperature anomaly pattern, the distribution of temperature and water vapor in the upper troposphere is largely controlled by dynamics and much less by thermodynamics. The troposphere~stratosphere temperature dipole is fundamentally due to the rising of the tropopause associated with hydrostatic expansion and vertical ascent in regions of enhanced deep convection. The rising motion pushes colder upper-tropospheric air into the lower stratosphere where the climatological temperature gradient reverses. No such dipole anomaly exists in the moisture field.
Numerical experiments with the GEOS GCM show that while atmospheric dynamics are principally responsible for the generation of the basic structures of the temperature and moisture anomalies observed during ENSO, the interaction between the hydrologic cycle and radiation plays an important role in enhancing and modifying the response. The role of hydrologic cycle~radiation interaction is most important in rendering the atmosphere more unstable both columnwise and locally, through enhanced longwave heating in the middle and lower troposphere and cooling above. The enhanced instability leads to intensified Hadley and Walker circulations, which are accompanied by stronger latent heating and a more vigorous hydrologic cycle. The intensified hydrologic cycle promotes further warming and moistening of the middle and lower troposphere, and cooling and drying in the stratosphere. The radiation~dynamics feedback leads to a new equilibrium climate state in which the increased heat transport by convection into the upper troposphere and stratosphere is balanced by increased radiative cooling, which removes the local excessive heat buildup.
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- Ho, C.-H. , M.-D. Chou, M. Suarez, K.-M. Lau, and M. M.-H. Yan, 1998, Comparison of model-calculated and ERBE-retrieved clear-sky outgoing longwave radiation, Journal of Geophysical Research, 103, 11529-11536
[abstract]
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In order to validate radiative transfer models and identify sources of errors in the satellite retrieval of radiation budgets, model calculations of clear-sky outgoing longwave radiation (OLR) over oceans are compared with data from the Earth Radiation Budget Experiment (ERBE). The NASA Goddard Earth Observing System (GEOS-1) and the National Centers for Environmental Prediction and National Center for Atmospheric Research reanalyses of temperature and humidity and the Stratospheric Aerosol and Gas Experiment retrieval of the stratospheric humidity are used in the model calculations. Averaged over time (1985~1989) and space (60 °S-60 °N), the model-calculated clear-sky OLR has a positive bias of 1.9~2.3 W m−2 when compared with that of ERBE. Nearly all of the bias can be accounted for by the inclusion of the absorption due to CO2 in the 4.3-μm band and to the weak CO2 and O3 molecular lines distant from band centers. The use of the two different reanalyses has only a small effect on the flux calculations (∼0.4 W m−2). Consistent with suggestions by previous studies, ERBE is found to overestimate (underestimate) the clear-sky OLR over high humid (dry) regions due to incorrect identification of clear scenes in the ERBE retrievals. The importance of the upper tropospheric humidity in affecting the Earth radiation budget is also investigated. Although only ∼15% of the atmospheric humidity is contained in the region above the 600-hPa level, the upper troposphere is as important as the lower troposphere in contributing to the clear-sky OLR. ⓒ 1998 American Geophysical Union |
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- Ho, C.-H. , M.-D. Chou, M. Suarez, and K.-M. Lau, 1998, Effect of ice cloud on GCM climate simulations, Geophysical Research Letters, 25, 71-74
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The effect of the interaction of SW (shortwave, solar) radiation with ice clouds on climate simulations is studied using the GEOS (Goddard Earth Observing System) climate GCM (general circulation model) coupled with an ocean mixed-layer model. Due to much larger cloud particles, the single-scattering co-albedo of ice clouds is nearly ten times larger than that of water clouds, but the asymmetry factor is generally smaller. Offline calculations with a radiative transfer model show that inclusion of the ice cloud effect increases SW absorption in the upper troposphere and decreases the SW flux at the surface. For the earth-atmosphere system, the change in the SW absorption is small due to compensation of the co-albedo and asymmetry factor effects. The effect of ice clouds tends to increase the atmospheric stability by enhancing SW heating in the upper troposphere and reducing SW heating in the lower troposphere and at the surface. The GCM experiments demonstrate that the inclusion of ice clouds produces colder surface temperature, and leads to reduction in SW heating of the earth-atmosphere system associated with changes in surface albedo and in cloud distribution. The enhanced atmospheric stability leads to decreased high cloud amount by a maximum of 80% and to increased middle cloud by a maximum of 60% over the tropics. ⓒ 1998 American Geophysical Union |
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- Kratz, D. P., M.-D. Chou, M. M.-H. Yan, and C.-H. Ho, 1998, Minor trace gas radiative forcing calculations using the k-distribution method with one-parameter scaling, Journal of Geophysical Research, 103, 31647-31656
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The k distribution method with one-parameter pressure and temperature scaling, first developed for water vapor, has now been applied to the minor trace gas, (N2O, CH4, CFCs, and two minor bands of CO2) absorption in the infrared window region (800~1380 cm−1). The derivation of the k distributions is based upon an exponential sum fitting to the monochromatically calculated transmission functions at a predetermined reference pressure and temperature. For nonhomogeneous path lengths, one-parameter scaling is utilized in conjunction with the k distribution method. To determine the accuracies of the k distribution method as compared to the monochromatic calculations, fluxes and cooling rates are calculated for a wide variety of atmospheric conditions. For the entire 800~1380 cm−1 spectral range the effect of the minor trace gases on the fluxes calculated using the k distribution method is within 2.3% of the monochromatic method. In addition to being accurate, this method is computationally very fast. When implemented into the Goddard EOS general circulation model, the computing time for the longwave flux calculations is increased by only 20% despite the inclusion of the minor trace gas absorption bands. ⓒ 1998 American Geophysical Union |
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- Chou, M.-D., M. Suarez, C.-H. Ho, M. Yan, and K.-T. Lee, 1998, Parameterizations for cloud overlapping and shortwave single-scattering properties for use in general circulation and cloud ensemble models, Journal of Climate, 11, 202-214
[abstract]
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Parameterizations for cloud single-scattering properties and the scaling of optical thickness in a partial cloudiness condition have been developed for use in atmospheric models. Cloud optical properties are parameterized for four broad bands in the solar (or shortwave) spectrum; one in the ultraviolet and visible region and three in the infrared region. The extinction coefficient, single-scattering albedo, and asymmetry factor are parameterized separately for ice and water clouds. Based on high spectral-resolution calculations, the effective single-scattering coalbedo of a broad band is determined such that errors in the fluxes at the top of the atmosphere and at the surface are minimized. This parameterization introduces errors of a few percent in the absorption of shortwave radiation in the atmosphere and at the surface.
Scaling of the optical thickness is based on the maximum-random cloud-overlapping approximation. The atmosphere is divided into three height groups separated approximately by the 400- and 700-mb levels. Clouds are assumed maximally overlapped within each height group and randomly overlapped among different groups. The scaling is applied only to the maximally overlapped cloud layers in individual height groups. The scaling as a function of the optical thickness, cloud amount, and the solar zenith angle is derived from detailed calculations and empirically adjusted to minimize errors in the fluxes at the top of the atmosphere and at the surface. Different scaling is used for direct and diffuse radiation. Except for a large solar zenith angle, the error in fluxes introduced by the scaling is only a few percent. In terms of absolute error, it is within a few watts per square meter.
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- Lau, K.-M., C.-H. Ho, and M.-D. Chou, 1996, Water vapor and cloud feedback over the tropical oceans: Can we use ENSO as a surrogate for the climate change?, Geophysical Research Letters, 23, 2971-2974
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Based on experiments with the Goddard Earth Observing System (GEOS) global climate model we find that the basic patterns of anomalous water vapor greenhouse effect and cloud radiative forcing during ENSO are primarily determined by the basin-wide dynamical response to large scale sea surface temperature (SST) forcing. There is no supergreenhouse effect in the sense of unstable interaction due to local thermodynamics and water vapor radiative feedback on interannual time scales. About 80% of the clear sky water vapor greenhouse sensitivity to SST-deduced from ENSO anomalies are due to the transport of water vapor by the large scale circulation. The sensitivity of water vapor greenhouse effect to SST due to radiative feedback is found to be about 1.8 Wm −2/ °C, much smaller than the values of 6~9 Wm −2/ °C previously estimated from satellite observations from ENSO conditions. Our results show that regionally based interannual variability should not be used to infer radiative feedback sensitivity for climate change unless proper corrections are made for the effect of the large scale circulation. ⓒ American Geophysical Union 1996 |
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