scholarly journals Opposite responses of the Indian Ocean to the thermal forcing of the Tibetan Plateau before and after the onset of the South Asian monsoon

2021 ◽  
pp. 1-56
Author(s):  
Yu Zhao ◽  
Anmin Duan ◽  
Guoxiong Wu
Keyword(s):  
Indian Ocean ◽  
Tibetan Plateau ◽  
South Asian ◽  
Asian Monsoon ◽  
Monsoon Onset ◽  
The Tibetan Plateau ◽  
Thermal Forcing ◽  
The North ◽  
Before And After ◽  
The Indian Ocean

AbstractThe atmospheric circulation changes dramatically over a few days before and after the onset of the South Asian monsoon in spring. It is accompanied by the annual maximum surface heating over the Tibetan Plateau. We conducted two sets of experiments with a coupled general circulation model to compare the response of atmospheric circulation and wind-driven circulation in the Indian Ocean to the thermal forcing of the Tibetan Plateau before and after the monsoon onset. The results show that the Tibetan Plateau's thermal forcing modulates the sea surface temperature (SST) of the Indian Ocean and the meridional circulation in the upper ocean with opposite effects during these two stages. The thermal forcing of the Tibetan Plateau always induces a southwesterly response over the northern Indian Ocean and weakens the northeasterly background circulation before the monsoon onset. Subsequently, wind-evaporation feedback results in a warming SST response. Meanwhile, the oceanic meridional circulation shows offshore upwellings in the north and southward transport in the upper layer crossing the equator, sinking near 15°S. After the monsoon onset, the thermal forcing of the Tibetan Plateau accelerates the background southwesterly and introduces a cooling response to the Indian Ocean SST. The response of oceanic meridional overturning circulation is limited to the north of the equator due to the location and structural evolution of the climatological local Hadley circulation. With an acceleration of the local Walker circulation, the underlying zonal currents also show corresponding changes, including a westerly drift along the equator, downwelling near Indonesia, offshore upwelling near Somalia, and a westward undercurrent.

scholarly journals The advanced South Asian monsoon onset accelerates lake expansion over the Tibetan Plateau

2019 ◽  
Vol 64 (20) ◽  
pp. 1486-1489 ◽  
Author(s):  
Yong Liu ◽  
Huopo Chen ◽  
Guoqing Zhang ◽  
Jianqi Sun ◽  
Huijun Wang
Keyword(s):  
Tibetan Plateau ◽  
South Asian ◽  
Asian Monsoon ◽  
Monsoon Onset ◽  
South Asian Monsoon ◽  
The Tibetan Plateau

scholarly journals The Mechanical Impact of the Tibetan Plateau on the Seasonal Evolution of the South Asian Monsoon

2012 ◽  
Vol 25 (7) ◽  
pp. 2394-2407 ◽  
Author(s):  
Hyo-Seok Park ◽  
John C. H. Chiang ◽  
Simona Bordoni
Keyword(s):  
Tibetan Plateau ◽  
South Asian ◽  
South China ◽  
Asian Monsoon ◽  
Monsoon Onset ◽  
Monsoon Circulation ◽  
South Asian Monsoon ◽  
The Tibetan Plateau ◽  
Westerly Winds ◽  
Southern Tibetan Plateau

Abstract The impact of the Tibetan Plateau on the South Asian monsoon is examined using a hierarchy of atmospheric general circulation models. During the premonsoon season and monsoon onset (April–June), when westerly winds over the Southern Tibetan Plateau are still strong, the Tibetan Plateau triggers early monsoon rainfall downstream, particularly over the Bay of Bengal and South China. The downstream moist convection is accompanied by strong monsoonal low-level winds. In experiments where the Tibetan Plateau is removed, monsoon onset occurs about a month later, but the monsoon circulation becomes progressively stronger and reaches comparable strength during the mature phase. During the mature and decaying phase of monsoon (July–September), when westerly winds over the Southern Tibetan Plateau almost disappear, monsoon circulation strength is not much affected by the presence of the Tibetan Plateau. A dry dynamical core with east–west-oriented narrow mountains in the subtropics consistently simulates downstream convergence with background zonal westerlies over the mountain. In a moist atmosphere, the mechanically driven downstream convergence is expected to be associated with significant moisture convergence. The authors speculate that the mechanically driven downstream convergence in the presence of the Tibetan Plateau is responsible for zonally asymmetric monsoon onset, particularly over the Bay of Bengal and South China.

scholarly journals Association between regional monsoon onset in South Asia and Tibetan Plateau thermal forcing

2021 ◽  
Author(s):  
Die Hu ◽  
Anmin Duan ◽  
Ping Zhang
Keyword(s):  
Tibetan Plateau ◽  
South Asian ◽  
Summer Monsoon ◽  
General Circulation ◽  
Diabatic Heating ◽  
Monsoon Onset ◽  
South Asian High ◽  
The Tibetan Plateau ◽  
South Asian Summer Monsoon ◽  
Thermal Forcing

Abstract By using multiple data sources and two sensitivity experiments using the atmospheric general circulation model of CAM4.0, we investigated the effect of thermal forcing over the Tibetan Plateau (TP) on the onset of the South Asian summer monsoon, including over the Arabian Sea (AS) and India. Results indicate that the seesaw pattern of diabatic heating over the TP, with a southeastern–northwestern inverse distribution in May, shows a robust relationship with the date of monsoon onset over the AS and India, which is independent of the influences from ocean signals. A positive diabatic heating seesaw pattern can enhance the ascending (descending) motion over the southeastern (northwestern) TP, corresponding to above (below) normal in- situ precipitation. Temperature budget diagnosis reveals that the adiabatic heating by the anomalous vertical motion and relevant horizontal advection of temperature convergence in the mid-upper troposphere are contributors to the warming over the TP. Consequently, the transition of the meridional temperature gradient over South Asian regions occurs earlier. Furthermore, the diabatic heating over the TP induces an enhanced and westward-extended South Asian high (SAH), which together with the easterly along the southern flank of the SAH superimpose on the low-level westerly flow over the AS and India, resulting in intensive upper-level divergence-pumping and upward motion. This anomalous circulation configuration in lower and upper levels further facilitates an earlier onset of summer monsoon in these two regions. These findings are corroborated in the sensitivity runs based on CAM4.0.

scholarly journals Response of the Indian Ocean to the Tibetan Plateau Thermal Forcing in Late Spring

2019 ◽  
Vol 32 (20) ◽  
pp. 6917-6938 ◽  
Author(s):  
Yu Zhao ◽  
Anmin Duan ◽  
Guoxiong Wu ◽  
Ruizao Sun
Keyword(s):  
Indian Ocean ◽  
Tibetan Plateau ◽  
Mixed Layer ◽  
General Circulation ◽  
Late Spring ◽  
Water Volume ◽  
The Tibetan Plateau ◽  
Northern Indian Ocean ◽  
Thermal Forcing ◽  
The Indian Ocean

Abstract The thermal effect of the Tibetan Plateau (TP) is known to exert substantial impacts on the atmospheric general circulation, suggesting that it may also influence the wind-driven circulation in the ocean through air–sea interactions. Here, several coupled general circulation model experiments are performed in order to investigate the short-term response of the Indian Ocean to the TP surface heat source in late spring (May). The results indicate that positive TP heating anomalies can induce significant atmospheric circulation responses over the northern Indian Ocean, characterized by easterly anomalies in the upper troposphere due to the enhanced South Asian high and lower-level southwesterly anomalies from the heat pumping effect. As a result, the surface wind speed over the northern Indian Ocean is reinforced, leading to intensified oceanic evaporation and subsequently cooler potential temperatures in the mixed layer. Wind-driven currents in the mixed layer are also affected. In the Bay of Bengal, Ekman transport facilitates water volume movement from west to east. In the Arabian Sea, water movement is weaker and the southward component is relatively more important. Both these areas show local meridional circulations with offshore upwelling in the northwest. Moreover, the cross-equatorial current is also enhanced in the eastern part of the tropical Indian Ocean. Overall, the upper layer in the northern Indian Ocean is efficiently modulated by the TP thermal forcing within one month.

scholarly journals Impacts of the Tibetan Plateau on Asian Climate

2016 ◽  
Vol 56 ◽  
pp. 7.1-7.29 ◽  
Author(s):  
Guoxiong Wu ◽  
Yimin Liu
Keyword(s):  
Boundary Layer ◽  
Tibetan Plateau ◽  
Asian Monsoon ◽  
Potential Temperature ◽  
The Tibetan Plateau ◽  
Thermal Forcing ◽  
The North ◽  
Summer Monsoon Onset ◽  
Constant Potential ◽  
Surface Sensible Heating

Abstract Professor Yanai is remembered in our hearts as an esteemed friend. Based on his accomplishments in tropical meteorology and with his flashes of insight he led his group at the University of California, Los Angeles, in the 1980s and 1990s to explore the thermal features of the Tibetan Plateau (TP) and its relation to the Asian monsoon, and he brought forward the TP meteorology established by Ye Duzheng et al. in 1957 to a new stage. In cherishing the memory of Professor Yanai and his great contribution to the TP meteorology, the authors review their recent study on the impacts of the TP and contribute this chapter as an extension of their chapter titled “Effects of the Tibetan Plateau” published by Yanai and Wu in 2006 in the book The Asian Monsoon. The influence of a large-scale orography on climate depends not only on the mechanical and thermal forcing it exerts on the atmosphere, but also on the background atmospheric circulation. In winter the TP possesses two leading heating modes resulting from the relevant dominant atmospheric circulations, in particular the North Atlantic Oscillation and the North Pacific Oscillation. The prevailing effect of the mechanical forcing of the TP in wintertime generates a dipole type of circulation, in which the anticyclonic gyre in the middle and high latitudes contributes to the warm inland area to the west, and the cold seashore area to the east, of northeast Asia, whereas the cyclonic gyre in low latitudes contributes to the formation of a prolonged dry season over central and southern Asia and moist climate over southeastern Asia. Such a dipole circulation also generates a unique persistent rainfall in early spring (PRES) over southern China. In 1980s, Yanai and his colleagues analyzed the in situ observation and found that the constant potential temperature boundary layer over the TP can reach about 300 hPa before the summer monsoon onset. This study supports these findings, and demonstrates that such a boundary layer structure is a consequence of the atmospheric thermal adaptation to the surface sensible heating, which vanishes quickly with increasing height. The overshooting of rising air, which is induced by surface sensible heating, then can form a layer of constant potential temperature with a thickness of several kilometers. The thermal forcing of the TP on the lower tropospheric circulation looks like a sensible heat–driven air pump (SHAP). It is the surface sensible heating on the sloping sides of the plateau that the SHAP can effectively influence the Asian monsoon circulation. In spring the SHAP contributes to the seasonal abrupt change of the Asian circulation and anchors the earliest Asian summer monsoon onset over the eastern Bay of Bengal. In summer, this pumping, together with the thermal forcing over the Iranian Plateau, produces bimodality in the South Asian high activity in the upper troposphere, which is closely related to the climate anomaly patterns over South and East Asia. Because the isentropic surfaces in the middle and lower troposphere intersect with the TP, in summertime the plateau becomes a strong negative vorticity source of the atmosphere and affects the surrounding climate and even the Northern Hemispheric circulation via Rossby wave energy dispersion. Future prospects in related TP studies are also addressed.

scholarly journals The Effect of ENSO on Tibetan Plateau Snow Depth: A Stationary Wave Teleconnection Mechanism and Implications for the South Asian Monsoons

2005 ◽  
Vol 18 (12) ◽  
pp. 2067-2079 ◽  
Author(s):  
Jeffrey Shaman ◽  
Eli Tziperman
Keyword(s):  
Tibetan Plateau ◽  
South Asian ◽  
Snow Depth ◽  
Rossby Waves ◽  
Stationary Wave ◽  
The Tibetan Plateau ◽  
The South ◽  
Central Pacific ◽  
The North ◽  
Asian Monsoons

Abstract An atmospheric stationary wave teleconnection mechanism is proposed to explain how ENSO may affect the Tibetan Plateau snow depth and thereby the south Asian monsoons. Using statistical analysis, the short available record of satellite estimates of snow depth, and ray tracing, it is shown that wintertime ENSO conditions in the central Pacific may produce stationary barotropic Rossby waves in the troposphere with a northeastward group velocity. These waves reflect off the North American jet, turning equatorward, and enter the North African–Asian jet over the eastern Atlantic Ocean. Once there, the waves move with the jet across North Africa, South Asia, the Himalayas, and China. Anomalous increases in upper-tropospheric potential vorticity and increased wintertime snowfall over the Tibetan Plateau are speculated to be associated with these Rossby waves. The increased snowfall produces a larger Tibetan Plateau snowpack, which persists through the spring and summer, and weakens the intensity of the south Asian summer monsoons.

scholarly journals Quantitative Analysis of Water Vapor Transport during Mei-Yu Front Rainstorm Period over the Tibetan Plateau and Yangtze-Huai River Basin

2019 ◽  
Vol 2019 ◽  
pp. 1-14 ◽  
Author(s):  
Hao Yang ◽  
Guan-yu Xu ◽  
Xiaofang Wang ◽  
Chunguang Cui ◽  
Jingyu Wang ◽  
...  
Keyword(s):  
Water Vapor ◽  
Indian Ocean ◽  
Tibetan Plateau ◽  
Heavy Rainfall ◽  
Initial Position ◽  
Vapor Transport ◽  
Water Vapor Transport ◽  
The Tibetan Plateau ◽  
Huai River ◽  
The Indian Ocean

There are continuous precipitation systems moving eastward from the Tibetan Plateau to the middle and lower reaches of the Yangtze-Huai River during the Mei-yu period. We selected 20 typical Mei-yu front precipitation cases from 2010 to 2015 based on observational and reanalysis data and studied the characteristics of their environmental fields. We quantitatively analyzed the transport and sources of water vapor in the rainstorms using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT_4.9) model. All 20 Mei-yu front precipitation cases occurred in a wide region from the Tibetan Plateau to the Yangtze-Huai River. The South Asian high and upper level jet stream both had strong intensities during the Mei-yu front rainstorm periods. Heavy rainfall mainly occurred in the divergence zone to the right of the high-level jet and in the convergence zone of the low-level jet, where strong vertical upward flows provided the dynamic conditions required for heavy rainfall. The water vapor mainly originated from the Indian Ocean, Bay of Bengal, and South China Sea. 52% of the air masses over the western Tibetan Plateau originated from Central Asia, which were rich in water vapor. The water vapor contribution at the initial position was only 41.5% due to the dry, cold air mass over Eurasia, but increased to 47.6% at the final position. Over the eastern Tibetan Plateau to the Sichuan Basin region, 40% of the air parcels came from the Indian Ocean, which was the main channel for water vapor transport. For the middle and lower reaches of the Yangtze River, 37% of the air parcels originated from the warm and humid Indian Ocean. The water vapor contribution at the initial position was 38.6%, but increased to 40.2% after long-distance transportation.

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