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RISS 인기검색어
- 검색키워드
- 저자 : Sang-Wook Yeh (검색결과 143 건)
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Contributions of Asian pollution and SST forcings on precipitation change in the North Pacific
Yeh, Sang-Wook,So, Jihyeon,Lee, Jong-Won,Kim, Minjoong J.,Jeong, Jaein I.,Park, Rokjin J. Elsevier Science Publishers 2017 Atmospheric research Vol.192 No.-
<P><B>Abstract</B></P> <P>East Asia has a significant concentration of pollutant aerosols, mostly due to rapid industrialization. Previous research indicates that the aerosol effect from Asian pollution outflow could account for the trend of increasing deep convective clouds, as well as an intensification of the storm track, over the North Pacific Ocean in winter since the mid-1990s. However, it is not clear whether such change is solely due to Asian pollutant forcings or not. To understand the relative roles of Asian pollutant aerosols and sea surface temperature (SST) forcings on the precipitation change in the North Pacific, we examine the interannual variation of particulate matter 2.5 (PM<SUB>2.5</SUB>) simulated in the global chemical transport model (GEOS-Chem) and the idealized experiments using the Community Atmosphere Model version 5 (CAM5) for 1986–2010. The composite analysis indicates that the changes in precipitation amount and storm track intensity in the southwestern North Pacific might be associated with the increase in PM<SUB>2.5</SUB> concentration in East China. However, El Niño-like warming during the years of high PM<SUB>2.5</SUB> concentration may also influence the precipitation amount, as well as the storm track intensity in the central and eastern North Pacific. Model experiments also indicate that the El Niño-like warming and the Asian pollutant aerosols have different effects on precipitation amounts in the North Pacific. Therefore, the precipitation changes, as well as the intensification of the storm track, in the North Pacific might be attributed to both Asian pollutant aerosols and SST forcing in the tropics.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Previous argument that the precipitation and storm track in the North Pacific is largely influenced by Asian pollutant forcings is re-examined. </LI> <LI> The changes in precipitation amount and storm track intensity in the North Pacific might be associated with the increase in PM<SUB>2.5</SUB> concentration in East China. However, El Niño-like warming during the years of high PM<SUB>2.5</SUB> concentration may also influence the precipitation amount, as well as the storm track intensity. </LI> <LI> Idealized model experiments are conducted and the result also indicate that the El Niño-like warming and the Asian pollutant aerosols have different effects on precipitation amounts in the North Pacific. </LI> <LI> The precipitation changes, as well as the intensification of the storm track, in the North Pacific might be attributed to both Asian pollutant aerosols and SST forcing in the tropics. </LI> </UL> </P>
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Yeh, Sang-Wook,Kug, Jong-Seong,Dewitte, Boris,Kwon, Min-Ho,Kirtman, Ben P.,Jin, Fei-Fei Macmillan Publishers Limited. All rights reserved 2009 Nature Vol.461 No.7263
<P>El Nino events, characterized by anomalous warming in the eastern equatorial Pacific Ocean, have global climatic teleconnections and are the most dominant feature of cyclic climate variability on subdecadal timescales. Understanding changes in the frequency or characteristics of El Nino events in a changing climate is therefore of broad scientific and socioeconomic interest. Recent studies(1-5) show that the canonical El Nino has become less frequent and that a different kind of El Nino has become more common during the late twentieth century, in which warm sea surface temperatures (SSTs) in the central Pacific are flanked on the east and west by cooler SSTs. This type of El Nino, termed the central Pacific El Nino (CP-El Nino; also termed the dateline El Nino(2), El Nino Modoki(3) or warm pool El Nino(5)), differs from the canonical eastern Pacific El Nino (EP-El Nino) in both the location of maximum SST anomalies and tropical-midlatitude teleconnections. Here we show changes in the ratio of CP-El Nino to EP-El Nino under projected global warming scenarios from the Coupled Model Intercomparison Project phase 3 multi-model data set(6). Using calculations based on historical El Nino indices, we find that projections of anthropogenic climate change are associated with an increased frequency of the CP-El Nino compared to the EP-El Nino. When restricted to the six climate models with the best representation of the twentieth-century ratio of CP-El Nino to EP-El Nino, the occurrence ratio of CP-El Nino/EP-El Nino is projected to increase as much as five times under global warming. The change is related to a flattening of the thermocline in the equatorial Pacific.</P>
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The Record-Breaking Heat Wave in 2016 over South Korea and Its Physical Mechanism
Yeh, Sang-Wook,Won, You-Jin,Hong, Jin-Sil,Lee, Kang-Jin,Kwon, MinHo,Seo, Kyong-Hwan,Ham, Yoo-Geun AMERICAN METEOROLOGICAL SOCIETY 2018 Monthly weather review Vol.146 No.5
<P>It is important to understand the dynamical processes that cause heat waves at regional scales. This study examined the physical mechanism that was responsible for a heat wave in South Korea in August 2016. Unlike previous August heat waves over the Korean Peninsula, the intensity of the geopotential height over the Kamchatka Peninsula in August 2016 was the strongest since 1979, which acted as an atmospheric blocking in the downstream region of the Korean Peninsula. Therefore, the anomalous high geopotential height in Mongolia, where the surface temperature was quite high, was observed persistently in August 2016. This anomalous high in Mongolia induced northerly winds with warm temperatures onto the Korean Peninsula, which contributed to a heat wave in August 2016. We further showed that the anomalous high geopotential height over the Kamchatka Peninsula in August 2016 was triggered by strong convection in the western-to-central subtropical Pacific through atmospheric teleconnections, which was quite different from a typical heat wave over the Korean Peninsula, in which convective forcing around the South China Sea is strong. This implies that convective forcing in the subtropical Pacific should also be monitored to predict heat wave events in East Asia, including South Korea. On the other hand, the zonal wave train associated with the circumglobal teleconnection pattern is also associated with the anomalous high geopotential height around Mongolia and the Kamchatka Peninsula, which may have contributed to the heat wave in August 2016.</P>
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Impact of the Indian Ocean on ENSO variability in a hybrid coupled model
Yeh, Sang-Wook,Wu, Renguang,Kirtman, Ben P. John WileySons, Ltd. 2007 Quarterly journal of the Royal Meteorological Soci Vol.133 No.623
<P>This study examines the impact of the Indian Ocean on El Niño and the Southern Oscillation (ENSO) variability through a series of numerical experiments with a hybrid coupled model. In the control run, an atmospheric general circulation model (AGCM) is coupled to the Zebiak–Cane simple ocean model in the tropical Pacific. Outside the tropical Pacific climatological sea surface temperatures are prescribed in the control simulation. In the first experiment, sea surface temperature anomalies (SSTAs) in the Indian Ocean are statistically predicted based on the state of the Pacific, and used to force the atmosphere. In the second experiment, a slab thermodynamic mixed layer model is coupled to the AGCM in the Indian Ocean. The Indian Ocean modifies the ENSO frequency via interactions with the Indian monsoon, but only when air–sea interactions in the Indian Ocean are included in the experimental design (i.e. the second experiment). The inclusion of the Indian Ocean, however, has little impact on the ENSO amplitude, which is at variance with other coupled simulations, suggesting that some missing dynamics or physics (i.e. Indian Ocean dynamics, Indonesian Throughflow, etc.) may play an important role. The Indian summer monsoon is more tightly coupled to ENSO in the second experiment than in the control run and the first experiment. The power spectrum of the Indian monsoon rainfall has a significant biennial time-scale of around 20–30 months in the second experiment, which may enhance the biennial time-scale of ENSO variability through a shift of the horizontal structure of zonal wind stress variability in the central equatorial Pacific. Copyright © 2007 Royal Meteorological Society</P>
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Changes in the spatial structure of strong and moderate El Niño events under global warming
Yeh, Sang‐,Wook,Kim, Hera,Kwon, MinHo,Dewitte, Boris John Wiley Sons, Ltd 2014 International journal of climatology Vol.34 No.8
<P><B>Abstract</B></P><P>In this study, we examine how the spatial structures of strong and moderate El Niño events have changed due to global warming using the Coupled Model Intercomparison Project Phase 5 (CMIP5) coupled general circulation models (CGCMs) based on a historical run and a Representative Concentration Pathways (RCP)4.5 run. The centre of the maximum anomalous sea surface temperature (SST) in the moderate El Niño has shifted significantly westward from the historical run to the RCP4.5 run; however, this is not seen with the strong El Niño events. Further analysis indicates that the centre of the maximum anomalous SST in the moderate El Niño with a negative Pacific Decadal Oscillation (PDO) phase shifted westward around the international dateline from the historical run to the RCP4.5 run. This is in contrast to the moderate El Niño, which shows a positive PDO phase. We also briefly discuss a possible mechanism on the change in the spatial structure of moderate El Niño with a negative phase of PDO from the historical run to the RCP4.5 run.</P>
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