scholarly journals Genesis of Upper-Tropospheric Anticyclones over the Asian−Western Pacific Sector from Tropical-extratropical Interaction Perspective

2021 ◽  
pp. 1-34
Keyword(s):  
Asian Summer Monsoon ◽  
Summer Monsoon Rainfall ◽  
Planetary Waves ◽  
Western Pacific ◽  
Formation Mechanisms ◽  
South Asian High ◽  
The Tibetan Plateau ◽  
The South ◽  
Maritime Continent ◽  
June July

Abstract Upper-tropospheric anticyclones (UTACs) emerge throughout the seasons with changing location and intensity. Here, the formation mechanisms of these UTACs, especially in the Asian-Australian-western Pacific sector, were investigated based on the diagnosis of the vorticity equation as well as the contribution of the planetary waves. During June-July-August (JJA), a vigorous UTAC corresponding to the South Asian High (SAH) forms over South Asia, to the south of the Tibetan Plateau, where intense heating associated with the Asian summer monsoon rainfall and the resultant baroclinic Rossby response are the important physical processes. Meanwhile, the produced anticyclonic vorticity is further transported by the inter-hemispheric divergent wind toward the Southern Hemisphere (SH), creating the SH UTAC centered over the Maritime Continent. During December-January-February (DJF), two zonally elongated UTACs reside on each side of the equator (~10° poleward), mainly over the Maritime Continent-western Pacific sector. Upon a closer look at the NH winter, we observed that the northern parts of UTAC cannot be explained by this vorticity balance alone. Diagnosis of the wave activity flux indicated that planetary waves emanating from the cold Eurasian continent converges around the northern parts of the UTAC with its peak in the NH winter, which weakens the subtropical jet, thus generating UTAC. Configuration of the SH summer (DJF) UTAC bears resemblance with that of SAH. These results suggest that the creation of anticyclonic vorticity and its inter-hemispheric transportation as well as the propagation of planetary wave are the selectively important agents for the genesis of seasonally varying UTACs.

scholarly journals Role of the South Asian High in the Onset Process of the Asian Summer Monsoon during Spring-to-Summer Transition

Atmosphere ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 239 ◽  
Author(s):  
Wei Wei ◽  
Yuting Wu ◽  
Song Yang ◽  
Wen Zhou
Keyword(s):  
South Asian ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Tropical Indian Ocean ◽  
Western Pacific ◽  
South Asian High ◽  
The South ◽  
Easterly Wind ◽  
Upper Level ◽  
The Western Pacific

The evolution of the South Asian high (SAH) and its role in the onset process of the Asian summer monsoon (ASM) during the spring-to-summer transition are investigated by using the NCEP-DOE reanalysis II dataset, with a focus on climatology and interannual time scales. Our results show four sudden changes of the SAH in its Northwestward evolution from the Western Pacific to the South China Sea (SCS), the Indochina Peninsula and the South Asian plateaus, coincide with the ASM onset over the Bay of Bengal, the SCS, and the Indian summer monsoon region. The physical process for the mutual promotion between the SAH and ASM rainfall is revealed. Accompanying the SAH evolution, the upper-level Easterly wind along the Southern flank and the upper-level divergence associated with the SAH shift Northwestward accordingly. The upper-level Easterly wind coordinates with the lower-level Southwesterly wind, and forms the summer circulation structure in the ASM regions gradually. Besides, the upper-level divergence associated with the SAH enhances ascending motion in ASM regions and increases the monsoon rainfall accordingly. Subsequently, the latent heat associated with the monsoon rainfall in the monsoon onset region excites an anticyclone to its Northwest in the upper level, which keeps strengthening the SAH and moving it Northwestward. This mutual promotion between the SAH and ASM rainfall can be affected by the sea surface temperatures (SSTs) in the Western Pacific and tropical Indian Ocean in the previous month. Colder (warmer) SSTs over the Western Pacific and inactive (active) convection over the Southern Philippines suppress (favor) the Northwestward development of the SAH in late April. In addition, the warmer (colder) SSTs in the tropical Indian Ocean excites anomalous anticyclone (cyclone) in the upper level near the equator, which keeps the SAH in the lower latitudes (promotes the SAH to the North), and delays (advances) the mutual promotion between the SAH and ASM rainfall. As a result, the entire ASM onset process is later (earlier) than normal.

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 Movement, drivers and bimodality of the South Asian High

2016 ◽  
Vol 16 (22) ◽  
pp. 14755-14774 ◽  
Author(s):  
Matthias Nützel ◽  
Martin Dameris ◽  
Hella Garny
Keyword(s):  
South Asian ◽  
Wave Radiation ◽  
South Asian High ◽  
The Tibetan Plateau ◽  
The South ◽  
Model Studies ◽  
Monsoon System ◽  
Eastern Border ◽  
Environmental Prediction ◽  
The Tropics

Abstract. The South Asian High (SAH) is an important component of the summer monsoon system in Asia. In this study we investigate the location and drivers of the SAH at 100 hPa during the boreal summers of 1979 to 2014 on interannual, seasonal and synoptic timescales using seven reanalyses and observational data. Our comparison of the different reanalyses focuses especially on the bimodality of the SAH, i.e. the two preferred modes of the SAH centre location: the Iranian Plateau to the west and the Tibetan Plateau to the east. We find that only the National Centers for Environmental Prediction–National Center of Atmospheric Research (NCEP–NCAR) reanalysis shows a clear bimodal structure of the SAH centre distribution with respect to daily and pentad (5 day) mean data. Furthermore, the distribution of the SAH centre location is highly variable from year to year. As in simple model studies, which connect the SAH to heating in the tropics, we find that the mean seasonal cycle of the SAH and its centre are dominated by the expansion of convection in the South Asian region (70–130° E  ×  15–30° N) on the south-eastern border of the SAH. A composite analysis of precipitation and outgoing long-wave radiation data with respect to the location of the SAH centre reveals that a more westward (eastward) location of the SAH is related to stronger (weaker) convection and rainfall over India and weaker (stronger) precipitation over the western Pacific.

scholarly journals Insensitivity of the Summer South Asian High Intensity to a Warming Tibetan Plateau in Modern Reanalysis Datasets

2017 ◽  
Vol 30 (8) ◽  
pp. 3009-3024 ◽  
Author(s):  
Liguang Wu ◽  
Xiaofang Feng ◽  
Mei Liang
Keyword(s):  
Tibetan Plateau ◽  
South Asian ◽  
High Intensity ◽  
Thermal Condition ◽  
Sensible Heat Flux ◽  
South Asian High ◽  
The Tibetan Plateau ◽  
The South ◽  
Condition Change ◽  
Surface Sensible Heat Flux

The South Asia high (SAH) is a prominent circulation system of the Asian summer monsoon, exerting profound influences on the weather and climate in China and surrounding regions. Its formation and maintenance is closely associated with strong summertime continental heating in the form of surface sensible heat flux and the latent heat release in connection with the Asian monsoon. In this study, the possible response of the South Asian high intensity to the thermal condition change in the Tibetan Plateau is examined with four modern reanalysis datasets, including the Modern-Era Retrospective Analysis for Research and Applications (MERRA), MERRA version 2 (MERRA-2), the European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis (ERA-Interim), and the Japanese 55-year Reanalysis (JRA-55). Despite the surface air warming in the four modern reanalysis datasets, reduced surface wind speed in three of the reanalysis datasets, and decreased surface sensible heat flux in the MERRA-2 dataset, there is no statistically significant trend in the SAH intensity over the period 1979–2015. One of the possible reasons is that the response of the upper-level circulation to the thermal condition change of the Tibetan Plateau occurs mainly in the 200-hPa subtropical westerly jet stream, which is located far away from the center of the South Asian high. Thus the South Asian high intensity is not particularly sensitive to the thermal condition change of the Tibetan Plateau, while the center of the South Asian high intensity over the plateau exhibits a northward trend over the period.

scholarly journals Genesis of the South Asian High and Its Impact on the Asian Summer Monsoon Onset

2013 ◽  
Vol 26 (9) ◽  
pp. 2976-2991 ◽  
Author(s):  
Boqi Liu ◽  
Guoxiong Wu ◽  
Jiangyu Mao ◽  
Jinhai He
Keyword(s):  
South Asian ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Lower Troposphere ◽  
Monsoon Onset ◽  
South Asian High ◽  
The South ◽  
Subtropical Anticyclone ◽  
Summer Monsoon Onset ◽  
Asian Summer

Abstract The formation of the South Asian high (SAH) in spring and its impacts on the Asian summer monsoon onset are studied using daily 40-yr ECMWF Re-Analysis (ERA-40) data together with a climate-mean composite technique and potential vorticity–diabatic heating (PV–Q) analysis. Results demonstrate that, about 2 weeks before the Asian summer monsoon onset, a burst of convection over the southern Philippines produces a negative vorticity source to its north. The SAH in the upper troposphere over the South China Sea is then generated as an atmospheric response to this negative vorticity forcing with the streamline field manifesting a Gill-type pattern. Afterward, the persistent rainfall over the northern Indochinese peninsula causes the SAH to move westward toward the peninsula. Consequently, a trumpet-shaped flow field is formed to its southwest, resulting in divergence pumping and atmospheric ascent just over the southeastern Bay of Bengal (BOB). Near the surface, as a surface anticyclone is formed over the northern BOB, an SST warm pool is generated in the central–eastern BOB. This, together with SAH pumping, triggers the formation of a monsoon onset vortex (MOV) with strong surface southwesterly developed over the BOB. Enhanced air–sea interaction promotes the further development and northward migration of the MOV. Consequently, the wintertime zonal-orientated subtropical anticyclone belt in the lower troposphere splits, abundant water vapor is transported directly from the BOB to the subtropical continent, and heavy rainfall ensues; the atmospheric circulation changes from winter to summer conditions over the BOB and Asian summer monsoon onset occurs.

scholarly journals Interannual Variation of Summer Atmospheric Heat Source over the Tibetan Plateau and the Role of Convection around the Western Maritime Continent

2015 ◽  
Vol 29 (1) ◽  
pp. 121-138 ◽  
Author(s):  
Xingwen Jiang ◽  
Yueqing Li ◽  
Song Yang ◽  
Kun Yang ◽  
Junwen Chen
Keyword(s):  
Water Vapor ◽  
Tibetan Plateau ◽  
Heat Source ◽  
Interannual Variation ◽  
The Tibetan Plateau ◽  
The South ◽  
Maritime Continent ◽  
Southern Boundary ◽  
Atmospheric Heat Source ◽  
Atmospheric Heat

Abstract The impacts of summer atmospheric heat source over the Tibetan Plateau (TP) on regional climate variation have attracted extensive attention. However, few studies have focused on possible causes of the interannual variation of atmospheric heat source over the TP. Total heat (TH) is generally composed of three components: surface sensible heat, latent heat release of condensation (LH), and radiative convergence. In this study, it is found that interannual variation of summer TH is dominated by LH in the central and eastern TP. The atmospheric circulation patterns associated with the TH over the TP in June are different from those in July and August. Large TH is accompanied by a cyclone centered over the South China Sea in June, which is replaced by an anticyclone in July and August. The interannual variation of July–August TH over the central and eastern TP is significantly affected by convection around the western Maritime Continent (WMC) that modulates the LH over the southeastern TP. Enhanced WMC convection induces an anticyclone to the south of the TP, which favors water vapor transport to the southeastern TP and thus an increase in precipitation. Enhanced convection over the southeastern TP may exert a positive feedback on local precipitation through pumping more water vapor from the southern boundary. Both observations and model simulations indicate that the enhanced WMC convection can induce the anticyclone to the south of the TP and convection–circulation is important for maintenance of the anticyclone.

scholarly journals Potential impact of carbonaceous aerosols on the Upper Troposphere and Lower Stratosphere (UTLS) during Asian summer monsoon in a global model simulation

2017 ◽  
Author(s):  
Suvarna Fadnavis ◽  
Gayatry Kalita ◽  
K. Ravi Kumar ◽  
Blaz Gasparini ◽  
Jui-Lin Frank Li
Keyword(s):  
Summer Monsoon ◽  
Radiative Forcing ◽  
Asian Summer Monsoon ◽  
Radiative Heating ◽  
The Tibetan Plateau ◽  
Carbonaceous Aerosols ◽  
The South ◽  
Upper Troposphere ◽  
North East ◽  
Asian Summer

Abstract. Recent satellite observations show efficient vertical transport of Asian pollutants from the surface to the upper level anticyclone by deep monsoon convection. In this paper, we examine the transport of carbonaceous aerosols including Black Carbon (BC) and Organic Carbon (OC) into the monsoon anticyclone using of ECHAM6-HAM, a global aerosol climate model. Further, we investigate impacts of enhanced (doubled) carbonaceous aerosols emissions on the UTLS from sensitivity simulations. These model simulations show that boundary layer aerosols are transported into the monsoon anticyclone by the strong monsoon convection from the Bay of Bengal, southern slopes of the Himalayas and the South China Sea. Doubling of emissions of BC and OC aerosols, each, over the South East Asia (10° S–50° N; 65° E–155° E) shows that lofted aerosols produce significant warming in the mid/upper troposphere. These aerosols lead to an increase in temperature by 1 K–3 K in the mid/upper troposphere and in radiative heating rates by 0.005 K/day near the tropopause. They alter aerosol radiative forcing at the surface by −1.4 W/m2; at the Top Of the Atmosphere (TOA) by +1.2 W/m2 and in the atmosphere by 2.7 W/m2 over the Asian summer monsoon region (20° N–40° N, 60° E–120° E). Atmospheric warming increases vertical velocities and thereby cloud ice in the upper troposphere. An anomalous warming over the Tibetan Plateau (TP) facilitate the relative strengthening of the monsoon Hadley circulation and elicit enhancement in precipitation over India and north east China.

Dynamic effects of the South Asian high on the ozone valley over the Tibetan Plateau

2012 ◽  
Vol 26 (2) ◽  
pp. 216-228 ◽  
Author(s):  
Dong Guo ◽  
Panxing Wang ◽  
Xiuji Zhou ◽  
Yu Liu ◽  
Weiliang Li
Keyword(s):  
Tibetan Plateau ◽  
South Asian ◽  
South Asian High ◽  
The Tibetan Plateau ◽  
Dynamic Effects ◽  
The South

scholarly journals Land–atmosphere–ocean coupling associated with the Tibetan Plateau and its climate impacts

2020 ◽  
Vol 7 (3) ◽  
pp. 534-552 ◽  
Author(s):  
Yimin Liu ◽  
Mengmeng Lu ◽  
Haijun Yang ◽  
Anmin Duan ◽  
Bian He ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Summer Monsoon ◽  
Thermal State ◽  
Asian Summer Monsoon ◽  
Climate Impacts ◽  
Meridional Overturning Circulation ◽  
South Asian High ◽  
The Tibetan Plateau ◽  
Ocean Coupling ◽  
Asian Summer

Abstract This paper reviews recent advances regarding land–atmosphere–ocean coupling associated with the Tibetan Plateau (TP) and its climatic impacts. Thermal forcing over the TP interacts strongly with that over the Iranian Plateau, forming a coupled heating system that elevates the tropopause, generates a monsoonal meridional circulation over South Asia and creates conditions of large-scale ascent favorable for Asian summer monsoon development. TP heating leads to intensification and westward extension (northward movement) of the South Asian High (Atlantic Intertropical Convergence Zone), and exerts strong impacts on upstream climate variations from North Atlantic to West Asia. It also affects oceanic circulation and buoyancy fields via atmospheric stationary wave trains and air–sea interaction processes, contributing to formation of the Atlantic Meridional Overturning Circulation. The TP thermal state and atmospheric–oceanic conditions are highly interactive and Asian summer monsoon variability is controlled synergistically by internal TP variability and external forcing factors.

Sign in / Sign up

Export Citation Format

Share Document