scholarly journals Role of the Surface Boundary Conditions in Boreal Spring on the Interannual Variability of the Multistage Evolution of the East Asian Summer Monsoon

2020 ◽  
Vol 33 (5) ◽  
pp. 1845-1861 ◽  
Author(s):  
Hyoeun Oh ◽  
Kyung-Ja Ha
Keyword(s):  
Boundary Conditions ◽  
Zonal Wind ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Surface Boundary ◽  
Eurasian Snow ◽  
Surface Boundary Conditions ◽  
Asian Summer ◽  
Upper Level ◽  
Upper Level Jet

AbstractThe seasonal movement of the upper-level jet plays a key role in the evolution of the East Asian summer monsoon (EASM). However, it remains unresolved how interannual changes in surface boundary conditions can influence the upper-level flow over East Asia, thereby modulating the onset of the EASM. Here we capture the timing of multistage evolution over East Asia using the upper-level zonal wind in a two-phase linear regression model. In addition, we show the impact of two surface boundary conditions on the timing of the EASM onset related to the strength of the upper-level zonal wind: 1) eastern Eurasian snow cover and 2) western North Pacific (WNP) sea surface temperature (SST) tendency. The eddy heat fluxes induced by the enhanced eastern Eurasian snow cover develop an anomalous anticyclonic circulation to the northwest, which causes anomalous warm southwesterly flow toward the north. These can make a reversal of the meridional temperature gradient, which results in the early monsoon onset via changes in the upper-level jet. The upper-level jet also responds to the SST tendency in April over the WNP via thermal wind balance and the resultant changes in transient eddy-induced heat transport. Our findings suggest potential sources for seasonal predictability in the interannual EASM onset dates.

Nonlinear, Intraseasonal Phases of the East Asian Summer Monsoon: Extraction and Analysis Using Self-Organizing Maps

2012 ◽  
Vol 25 (20) ◽  
pp. 6975-6988 ◽  
Author(s):  
Jung-Eun Chu ◽  
Saji N. Hameed ◽  
Kyung-Ja Ha
Keyword(s):  
Time Scales ◽  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Self Organizing Maps ◽  
Dry Spell ◽  
Asian Summer ◽  
Upper Level ◽  
Self Organizing

Abstract The hypothesis that regional characteristics of the East Asian summer monsoon (EASM) result from the presence of nonlinear coupled features that modulate the seasonal circulation and rainfall at the intraseasonal time scale is advanced in this study. To examine this hypothesis, the authors undertake the analysis of daily EASM variability using a nonlinear multivariate data classifying algorithm known as self-organizing mapping (SOM). On the basis of various SOM node analyses, four major intraseasonal phases of the EASM are identified. The first node describes a circulation state corresponding to weak tropical and subtropical pressure systems, strong upper-level jets, weakened monsoonal winds, and cyclonic upper-level vorticity. This mode, related to large rainfall anomalies in southeast China and southern Japan, is identified as the mei-yu–baiu phase. The second node represents a distinct circulation state corresponding to a strengthened subtropical high, monsoonal winds, and anticyclonic upper-level vorticity in southeast Korea, which is identified as the changma phase. The third node is related to copious rain over Korea following changma, which we name the postchangma phase. The fourth node is situated diagonally opposite the changma mode. Because Korea experiences a dry spell associated with this SOM node, it is referred to as the dry-spell phase. The authors also demonstrate that a strong modulation of the changma and dry-spell phases on interannual time scales occurs during El Niño and La Niña years. Results imply that the key to predictability of the EASM on interannual time scales may lie with analysis and exploitation of its nonlinear characteristics.

scholarly journals Synoptic Conditions Controlling the Seasonal Onset and Days of Heatwaves Over Korea

2021 ◽  
Author(s):  
Woosuk Choi ◽  
Chang-Hoi Ho ◽  
Jiyoung Jung ◽  
Minhee Chang ◽  
Kyung-Ja Ha
Keyword(s):  
Asian Summer Monsoon ◽  
Baroclinic Instability ◽  
Heat Exposure ◽  
Synoptic Conditions ◽  
Hot Days ◽  
Key Factor ◽  
Asian Summer ◽  
Upper Level ◽  
Upper Level Jet ◽  
Favorable Conditions

Abstract As global warming gets worse, the extreme heat exposure time is expected to increase. Considering that the heatwave damages increased by the accumulation of heat stress, it is important to understand the heatwave onset and number of heatwave days (HWDs). Here, we show that the end of East Asian summer monsoon activity (i.e., Changma retreat date, CRD) could be an indicator in determining the onset of the heatwave, and the barotropic structure induced by the circumglobal and Pacific–Japan teleconnections is a key factor in lengthening the number of HWDs in Korea. The onset of the heatwave is delayed when CRD belated than the climatology late over Korea due to sufficient moisture transportation between the edge of western North Pacific subtropical high and cold polar air mass in July. The number of HWDs from July through August over Korea shows a positive linear relationship with the synoptic stagnation index because the upper-layer anticyclone associated with stagnation is formed around Korea by zonal wave activity. Barotropic anticyclone stabilizes the atmosphere and increases the number of clear sky days, which possibly leads to hot days. Fewer HWDs are observed when there is baroclinic instability due to strong upper-level jet stream and synoptic-scale weather systems move smoothly. By identifying the meteorological mechanism of heatwave occurrence and favorable conditions for sustained hot days over Korea, our results are eventually able to contribute to reducing damages caused by heatwaves.

scholarly journals Synoptic conditions controlling the seasonal onset and days of heatwaves over Korea

2021 ◽  
Author(s):  
Woosuk Choi ◽  
Chang-Hoi Ho ◽  
Jiyoung Jung ◽  
Minhee Chang ◽  
Kyung-Ja Ha
Keyword(s):  
Asian Summer Monsoon ◽  
Baroclinic Instability ◽  
Heat Exposure ◽  
Synoptic Conditions ◽  
Hot Days ◽  
Key Factor ◽  
Asian Summer ◽  
Upper Level ◽  
Upper Level Jet ◽  
Favorable Conditions

AbstractAs global warming gets worse, the extreme heat exposure time is expected to increase. Considering that the heatwave damages increased by the accumulation of heat stress, it is important to understand the heatwave onset and number of heatwave days (HWDs). Here, we show that the end of East Asian summer monsoon activity (i.e., Changma retreat date, CRD) could be an indicator in determining the onset of the heatwave, and the barotropic structure induced by the circumglobal and Pacific–Japan teleconnections is a key factor in lengthening the number of HWDs in Korea. The onset of the heatwave is delayed when CRD belated than the climatology late over Korea due to sufficient moisture transportation between the edge of western North Pacific subtropical high and cold polar air mass in July. The number of HWDs from July through August over Korea shows a positive linear relationship with the synoptic stagnation index because the upper-layer anticyclone associated with stagnation is formed around Korea by zonal wave activity. Barotropic anticyclone stabilizes the atmosphere and increases the number of clear sky days, which possibly leads to hot days. Fewer HWDs are observed when there is baroclinic instability due to strong upper-level jet stream and synoptic-scale weather systems move smoothly. By identifying the meteorological mechanism of heatwave occurrence and favorable conditions for sustained hot days over Korea, our results are eventually able to contribute to reducing damages caused by heatwaves.

scholarly journals Seasonal prediction skill of East Asian summer monsoon in CMIP5-Models

2017 ◽  
Author(s):  
Bo Huang ◽  
Ulrich Cubasch ◽  
Christopher Kadow
Keyword(s):  
Summer Monsoon ◽  
Zonal Wind ◽  
East Asian Summer Monsoon ◽  
Southern Oscillation ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Prediction Skill ◽  
Cmip5 Models ◽  
Coupled Mode ◽  
Asian Summer

Abstract. The East Asian summer monsoon (EASM) is an important part of the global climate system and plays a vital role in the Asian climate. Its sub-seasonal-to-seasonal predictability is a long-standing issue within the monsoon scientist community. In this study, we analyse the seasonal (with six months lead time) prediction skill of the EASM rainfall and its associated general circulation in non-initialised and initialised simulations for the years 1979–2005 performed by six prediction systems (i.e., the BCC-CSM1-1, the CanCM4, the GFDL-CM2p1, the HadCM3, the MIROC5 and the MPI-ESM-LR) from the Coupled Model Intercomparison Project phase 5 (CMIP 5). We find that the simulation of the zonal wind is significantly improved in initialised simulations compared to non-initialized simulations. Based on the knowledge that zonal wind indices can be used as potential predictors for the EASM, we selected an EASM index based upon the zonal wind for further analysis. The assessment show that the GFDL-CM2p1 and the MIROC5 add prediction skill in simulating the EASM index with initialisation, the BCC-CSM1-1, the CanCM4, and the MPI-ESM-LR change the skill insignificantly, and the HadCM3 indicates a decreased skill score. The different response to the initialisation can be traced back to the ability of the models to capture the ENSO (El Niño-Southern Oscillation)-EASM coupled mode, particularly the Southern Oscillation-EASM coupled mode. In summary, we find that the GFDL-CM2p1 and the MIROC5 are capable to predict the EASM on a seasonal time-scale after initialisation.

scholarly journals Impact of Chinese Urbanization and Aerosol Emissions on the East Asian Summer Monsoon

2017 ◽  
Vol 30 (3) ◽  
pp. 1019-1039 ◽  
Author(s):  
Zhihong Jiang ◽  
Fei Huo ◽  
Hongyun Ma ◽  
Jie Song ◽  
Aiguo Dai
Keyword(s):  
Land Cover ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Latent Heating ◽  
Anthropogenic Aerosols ◽  
Urban Land Cover ◽  
Asian Summer ◽  
Upper Level ◽  
Aerosol Emissions

Abstract Impacts of urbanization and anthropogenic aerosols in China on the East Asian summer monsoon (EASM) are investigated using version 5.1 of the Community Atmosphere Model (CAM5.1) by comparing simulations with and without incorporating urban land cover and/or anthropogenic aerosol emissions. Results show that the increase of urban land cover causes large surface warming and an urban frictional drag, both leading to a northeasterly wind anomaly in the lower troposphere over eastern China (EC). This weakens the southerly winds associated with the EASM and causes a convergence anomaly in southern China (SC) with increased ascent, latent heating, and cloudiness. The enhanced latent heating reinforces surface convergence and upper-level divergence over SC, leading to more northward advection in the upper level into northern China (NC) and descending between 30° and 50°N over East Asia. Cloudiness reduction, adiabatic heating, and warm advection over NC all enhance the urban heating there, together causing anomalous tropospheric warming at those latitudes over East Asia. Anthropogenic aerosols cause widespread cooling at the surface and in the troposphere over EC, which decreases the summer land–ocean thermal contrast, leading to a weakened EASM circulation with reduced moisture transport to NC. This results in wetter and drier conditions over SC and NC, respectively. When both the urbanization and anthropogenic aerosols are included in the model, aerosols’ cooling is partially offset by the urban heating, and their joint effect on the circulation is dominated by the aerosols’ effect with a reduced magnitude. In the combined experiment, surface and tropospheric temperatures are also altered by the decrease (increase) in cloudiness over NC (SC) with most of the cooling confined to SC, which further weakens the EASM circulation.

scholarly journals The interaction of tropical and extratropical air masses controlling East Asian summer monsoon progression

2021 ◽  
Author(s):  
Ambrogio Volonté ◽  
Andrew G. Turner ◽  
Reinhard Schiemann ◽  
Pier Luigi Vidale ◽  
Nicholas P. Klingaman
Keyword(s):  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
The Tibetan Plateau ◽  
Primary Role ◽  
Air Masses ◽  
Low Level ◽  
Asian Summer ◽  
Upper Level

Abstract. The East Asian summer monsoon (EASM) is a complex phenomenon, influenced by both tropical and mid-latitude dynamics and by the presence of the Tibetan Plateau. The EASM front neatly separates tropical and extratropical air masses as the monsoon marches northwards. Although the different factors behind EASM progression are illustrated in a number of studies, their interactions, in particular between tropical and extratropical air masses, still need to be clarified. In this study we apply Eulerian and Lagrangian methods to the ERA5 reanalysis dataset to provide a comprehensive study of the seasonal evolution and variability of the EASM, and we highlight the dynamics of the air masses converging at its front. A frontal detection algorithm is used to perform a front-centred analysis of EASM evolution. The analysis highlights the primary role of the sub-tropical westerly jet (STWJ) in controlling the strength and the poleward progression of the EASM front, in particular during Mei Yu, one of the stages of EASM progression. The upper-level mid-latitude forcing acts in conjunction with the southerly advection of low-level moist tropical air, modulated by the seasonal cycle of the South Asian monsoon and by the location of the Western North Pacific subtropical high. The Mei Yu stage is distinguished by an especially clear interaction between tropical and mid-latitude air masses converging at the EASM front. The analysis of composites based on the latitude of the EASM front during Mei Yu reveals the influence of the STWJ on the strength of the mid-latitude flow impacting on the northern side of the EASM front. In turn, this affects the extent of the warm moist advection on its southern side and the distribution and intensity of resultant rainfall over China. This study shows the validity of an analysis of EASM evolution focused on its front and on the related low-level airstreams, at least in the Mei Yu stage. The framework highlighted shows how the upper-level flow drives the low-level airstreams that converge at the EASM front, thus controlling the shape of EASM progression. This framework provides a basis for studies of climate variability and extreme events and for model evaluation.

scholarly journals Seasonal prediction skill of East Asian summer monsoon in CMIP5 models

2018 ◽  
Vol 9 (3) ◽  
pp. 985-997
Author(s):  
Bo Huang ◽  
Ulrich Cubasch ◽  
Christopher Kadow
Keyword(s):  
Summer Monsoon ◽  
Zonal Wind ◽  
East Asian Summer Monsoon ◽  
Southern Oscillation ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Prediction Skill ◽  
Coupled Mode ◽  
Asian Summer ◽  
Prediction Systems

Abstract. The East Asian summer monsoon (EASM) is an important part of the global climate system and plays a vital role in the Asian climate. Its seasonal predictability is a long-standing issue within the monsoon scientist community. In this study, we analyse the seasonal (the leading time is at least 6 months) prediction skill of the EASM rainfall and its associated general circulation in non-initialised and initialised simulations for the years 1979–2005, which are performed by six prediction systems (i.e. the BCC-CSM1-1, the CanCM4, the GFDL-CM2p1, the HadCM3, the MIROC5, and the MPI-ESM-LR) from the Coupled Model Intercomparison Project phase 5 (CMIP 5). We find that most prediction systems of simulated zonal wind over 850 and 200 hPa are significantly improved in the initialised simulations compared to non-initialised simulations. Based on the knowledge that zonal wind indices can be used as potential predictors for the EASM, we select an EASM index based upon the zonal wind over 850 hPa for further analysis. This assessment shows that the GFDL-CM2p1 and the MIROC5 added prediction skill in simulating the EASM index with initialisation, the BCC-CSM1-1, the CanCM4, and the MPI-ESM-LR changed the skill insignificantly, and the HadCM3 indicates a decreased skill score. The different responses to initialisation can be traced back to the ability of the models to capture the ENSO (El Niño–Southern Oscillation) and EASM coupled mode, particularly the Southern Oscillation–EASM coupled mode. As is known from observation studies, this mode links the oceanic circulation and the EASM rainfall. Overall, the GFDL-CM2p1 and the MIROC5 are capable of predicting the EASM on a seasonal timescale under the current initialisation strategy.

Sign in / Sign up

Export Citation Format

Share Document