Impact of East Asian Summer Monsoon Heating on the Interannual Variation of the South Asian High

2015 ◽  
Vol 29 (1) ◽  
pp. 159-173 ◽  
Author(s):  
Pengfei Zhang ◽  
Yimin Liu ◽  
Bian He
Keyword(s):  
Middle East ◽  
South Asian ◽  
East Asian Summer Monsoon ◽  
Geopotential Height ◽  
Interannual Variation ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
South Asian High ◽  
Upper Troposphere ◽  
Asian Summer

Abstract Occupying the upper troposphere over subtropical Eurasia during boreal summer, the South Asian high (SAH) is thought to be a regulator of the East Asian summer monsoon (EASM), which is particularly important for regional climate over Asia. However, there is feedback of the condensational heating associated with EASM precipitation to SAH variability. In this study, interannual variation of SAH intensity and the mechanisms are investigated. For strong SAH cases, the high pressure system intensifies and expands. Significant positive anomalies of the geopotential height and upper-tropospheric temperature were found over the Middle East and to the east of the Tibetan Plateau (TP), namely, the western and the eastern flanks of the SAH. The dynamical diagnosis and the numerical experiments consistently show that the interannual variation of SAH intensity is strongly affected by EASM precipitation over the eastern TP–Yangtze River valley. The feedback of the condensational heating anomaly to the SAH is summarized as follows: Excessive EASM heating excites a local anticyclone in the upper troposphere and warms the upper troposphere, leading to the eastward extension of the SAH’s eastern edge and reinforcing geopotential height anomalies over East Asia. Furthermore, the monsoonal heating excites a westward-propagating Rossby wave that increases the upper-tropospheric geopotential height and warms the upper troposphere over the Middle East. In conclusion, this study suggests a mechanistic paradigm in which the EASM may also be a modulator of SAH variation rather than just a passive result of the latter as traditionally thought. The results suggest that the EASM and the SAH are a tightly interactive system.

scholarly journals Interannual Variation of the South Asian High and Its Relation with Indian and East Asian Summer Monsoon Rainfall

2015 ◽  
Vol 28 (7) ◽  
pp. 2623-2634 ◽  
Author(s):  
Wei Wei ◽  
Renhe Zhang ◽  
Min Wen ◽  
Baek-Jo Kim ◽  
Jae-Cheol Nam
Keyword(s):  
Latent Heat ◽  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Monsoon Rainfall ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Summer Monsoon Rainfall ◽  
South Asian High ◽  
Asian Summer ◽  
Asian Summer Monsoon Rainfall

Abstract A diagnostic analysis reveals that on the interannual time scale the southeast–northwest movement is a dominant feature of the South Asian high (SAH), and it is closely related to the Indian and East Asian summer monsoon rainfall. The southeastward (northwestward) shift of the SAH is closely related to less (more) Indian summer monsoon rainfall and more (less) rainfall in the Yangtze River valley (YRV) over the East Asian summer monsoon region. An anomalous AGCM is utilized to examine the effect of latent heat anomalies associated with the Asian summer monsoon rainfall on the SAH. The negative latent heat anomalies over the northern Indian Subcontinent associated with a weak Indian summer monsoon stimulates an anomalous cyclone to its northwest and an anticyclone to its northeast over the eastern Tibetan Plateau and eastern China in the upper troposphere, which is responsible for the east–west shift of the SAH and more rainfall in the YRV. The positive latent heat release associated with rainfall anomalies in the YRV excites a southward-located anticyclone over eastern China, exerting a feedback effect on the SAH and leading to a southeast–northwest shift of the SAH.

scholarly journals Upper tropospheric CO and O<sub>3</sub> budget during the Asian Summer Monsoon

2016 ◽  
Author(s):  
B. Barret ◽  
B. Sauvage ◽  
Y. Bennouna ◽  
E. Le Flochmoen
Keyword(s):  
South Asian ◽  
Summer Monsoon ◽  
Satellite Data ◽  
Large Scale ◽  
Transport Model ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Gangetic Plain ◽  
Upper Troposphere ◽  
Asian Summer

Abstract. During the Asian Summer Monsoon, the circulation in the Upper Troposphere-Lower Stratosphere (UTLS) is dominated by the Asian Monsoon Anticyclone (AMA). Pollutants convectively uplifted to the upper troposphere are trapped within this anticyclonic circulation that extends from the Pacific Ocean to the eastern Mediterranean basin. Among the uplifted pollutants are ozone (O3) and its precursors, such as carbon monoxide (CO) and nitrogen oxides (NOx). Many studies based on global modelisation and satellite data have documented the source regions and transport pathways of primary pollutants (CO, HCN) into the AMA. Here, we aim to quantify the O3 budget by taking into consideration anthropogenic and natural sources. We first use CO and O3 data from the Metop-A/IASI sensor to document their tropospheric distributions over Asia, taking advantage of the useful information they provide on the vertical dimension. These satellite data are used together with MOZAIC/IAGOS tropospheric profiles recorded in India to validate the distributions simulated by the global GEOS-Chem chemistry transport model. Over the Asian region, UTLS monthly CO and O3 distributions from IASI and GEOS-Chem display the same large-scale features. UTLS CO columns from GEOS-Chem are in agreement with IASI, with a low bias of 11 ± 9% and a correlation coefficient of 0.70. For O3, the model underestimates IASI UTLS columns over Asia by 14 ± 26% but the correlation between both is high (0.94). GEOS-Chem is further used to quantify the CO and O3 budget through sensitivity simulations. For CO, these simulations confirm that South-Asian anthropogenic emissions have a more important impact on enhanced concentrations within the AMA (∼25 ppbv) than East-Asian emissions (∼10 ppbv). The correlation between enhanced emissions over the Indo–gangetic–Plain and monsoon deep convection is responsible for this larger impact. Consistently, South-Asian anthropogenic NOx emissions also play a larger role in producing O3 within the AMA (∼8 ppbv) than East-Asian emissions (∼5 ppbv) but Asian lightning produced NOx are responsible for the largest O3 production (10–14 ppbv). Stratosphere to Troposphere Exchanges (STE) are also important in transporting O3 in the upper part of the AMA.

scholarly journals Upper-tropospheric CO and O<sub>3</sub> budget during the Asian summer monsoon

2016 ◽  
Vol 16 (14) ◽  
pp. 9129-9147 ◽  
Author(s):  
Brice Barret ◽  
Bastien Sauvage ◽  
Yasmine Bennouna ◽  
Eric Le Flochmoen
Keyword(s):  
South Asian ◽  
Summer Monsoon ◽  
Satellite Data ◽  
Large Scale ◽  
Transport Model ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Gangetic Plain ◽  
Upper Troposphere ◽  
Asian Summer

Abstract. During the Asian summer monsoon, the circulation in the upper troposphere/lower stratosphere (UTLS) is dominated by the Asian monsoon anticyclone (AMA). Pollutants convectively uplifted to the upper troposphere are trapped within this anticyclonic circulation that extends from the Pacific Ocean to the Eastern Mediterranean basin. Among the uplifted pollutants are ozone (O3) and its precursors, such as carbon monoxide (CO) and nitrogen oxides (NOx). Many studies based on global modeling and satellite data have documented the source regions and transport pathways of primary pollutants (CO, HCN) into the AMA. Here, we aim to quantify the O3 budget by taking into consideration anthropogenic and natural sources. We first use CO and O3 data from the MetOp-A/IASI sensor to document their tropospheric distributions over Asia, taking advantage of the useful information they provide on the vertical dimension. These satellite data are used together with MOZAIC tropospheric profiles recorded in India to validate the distributions simulated by the global GEOS-Chem chemistry transport model. Over the Asian region, UTLS monthly CO and O3 distributions from IASI and GEOS-Chem display the same large-scale features. UTLS CO columns from GEOS-Chem are in agreement with IASI, with a low bias of 11 ± 9 % and a correlation coefficient of 0.70. For O3, the model underestimates IASI UTLS columns over Asia by 14 ± 26 % but the correlation between both is high (0.94). GEOS-Chem is further used to quantify the CO and O3 budget through sensitivity simulations. For CO, these simulations confirm that South Asian anthropogenic emissions have a more important impact on enhanced concentrations within the AMA (∼  25 ppbv) than East Asian emissions (∼  10 ppbv). The correlation between enhanced emissions over the Indo-Gangetic Plain and monsoon deep convection is responsible for this larger impact. Consistently, South Asian anthropogenic NOx emissions also play a larger role in producing O3 within the AMA (∼  8 ppbv) than East Asian emissions (∼  5 ppbv), but Asian lightning-produced NOx is responsible for the largest O3 production (10–14 ppbv). Stratosphere-to-troposphere exchanges are also important in transporting O3 in the upper part of the AMA.

Is there interdecadal variation in the South Asian High?

2021 ◽  
pp. 1-46
Author(s):  
Dapeng Zhang ◽  
Yanyan Huang ◽  
BoTao Zhou ◽  
Huijun Wang
Keyword(s):  
South Asian ◽  
Geopotential Height ◽  
Yangtze River ◽  
North China ◽  
East Asian ◽  
Northwest Pacific ◽  
South Asian High ◽  
The Yangtze River ◽  
The South ◽  
Upper Troposphere

AbstractThe decadal intensification of the South Asian High (SAH) after the late 1970s, which is determined based on the geopotential height (H), is suspicious due to the lifting effect upon H caused by global warming. The updated reanalysis datasets of ERA5 and JRA55 indicate that the anticyclone in the upper troposphere over the Tibetan Plateau is relatively weak during 1980–2018 compared to that during 1950–1979. This decadal weakening of the SAH after 1979 can also be observed in the radiosonde observation data. Correspondingly, the SAH defined by eddy geopotential height (H’) reflects a consistent decadal weakening variation. The decadal weakening of SAH detected from H’ after the late 1970s matches with a decadal southward shift of the East Asian Westerly Jet, causing ascending motions over the Yangtze River Valley and descending motions over North China. Moreover, the decadal weakening and westward shift of the SAH is accompanied with the positive relative vorticity anomalies over the Northwest Pacific in the upper troposphere, which implies a declining and eastward shift of the western Pacific subtropical high (WPSH) and a weakened East Asian Summer Monsoon (EASM). Hence, the decadal weakening of the SAH after the late 1970s may contribute to the Yangtze-River-flooding-and-North-China-drought pattern through its connection with other circulation systems of EASM.

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