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 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 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 Comprehensive Pattern of Deep Convective Systems over the Tibetan Plateau–South Asian Monsoon Region Based on TRMM Data

2014 ◽  
Vol 27 (17) ◽  
pp. 6612-6626 ◽  
Author(s):  
Xiushu Qie ◽  
Xueke Wu ◽  
Tie Yuan ◽  
Jianchun Bian ◽  
Daren Lu
Keyword(s):  
Tibetan Plateau ◽  
South Asian ◽  
Asian Monsoon ◽  
South Asian Monsoon ◽  
The Tibetan Plateau ◽  
Lightning Flash ◽  
Monsoon Region ◽  
Asian Monsoon Region ◽  
Convective Systems ◽  
Deep Convective Systems

Abstract Diurnal and seasonal variation, intensity, and structure of deep convective systems (DCSs; with 20-dBZ echo tops exceeding 14 km) over the Tibetan Plateau–South Asian monsoon region from the Tibetan Plateau (TP) to the ocean are investigated using 14 yr of Tropical Rainfall Measuring Mission (TRMM) data. Four unique regions characterized by different orography are selected for comparison, including the TP, the southern Himalayan front (SHF), the South Asian subcontinent (SAS), and the ocean. DCSs and intense DCSs (IDCSs; with 40-dBZ echo tops exceeding 10 km) occur more frequently over the continent than over the ocean. About 23% of total DCSs develop into IDCSs in the SHF, followed by the TP (21%) and the SAS (15%), with the least over the ocean (2%). The average 20-dBZ echo-top height of IDCSs exceeds 16 km and 9% of them even exceed 18 km. DCSs and IDCSs are the most frequent over the SHF, especially in the westernmost SHF, where the intensity—in terms of strong radar echo-top (viz., 40 dBZ) height, ice-particle content, and lightning flash rate—is the strongest. DCSs over the TP are relatively weak in convective intensity and small in size but occur frequently. Oceanic DCSs possess the tallest cloud top (which mainly reflects small ice particles) and the largest size, but their convective intensity is markedly weaker. DCSs and IDCSs show a similar diurnal variation, mainly occurring in the afternoon with a peak at 1600 local time over land. Although most of both DCSs and IDCSs occur between April and October, DCSs have a peak in August, whereas IDCSs have a peak in May.

scholarly journals Reexamining the barrier effect of Tibetan Plateau on the South Asian summer monsoon

2013 ◽  
Vol 9 (4) ◽  
pp. 5019-5036
Author(s):  
G.-S. Chen ◽  
Z. Liu ◽  
J. E. Kutzbach
Keyword(s):  
Tibetan Plateau ◽  
South Asian ◽  
Summer Monsoon ◽  
Asian Monsoon ◽  
Asian Summer Monsoon ◽  
Monsoon Circulation ◽  
The Tibetan Plateau ◽  
South Asian Summer Monsoon ◽  
The South ◽  
Monsoon System

Abstract. The Tibetan Plateau has been conventionally treated as an elevated heat source driving the Asian monsoon system, especially for the South Asian monsoon. Numerous model simulations with general circulation models (GCMs) support this hypothesis with the finding that the Asian monsoon system is weak or absent with all elevated topographies removed. A recent model simulation shows that the South Asian summer monsoon circulation is little affected with only the Himalayas (no Tibetan Plateau) kept as a barrier, leading to a hypothesis of the barrier "blocking" mechanism of the Tibetan Plateau. In this paper, a new series of experiments are designed to reexamine this barrier effect. We find that with the barrier, the large-scale summer monsoon circulation over South Asia is simulated in general agreement with the full Tibetan Plateau, which is consistent with the previous finding. However there remains significant differences in both wind field and precipitation field elsewhere, suggesting a role of the full Tibetan Plateau as well. Moreover, the proposed barrier "blocking" mechanism is not found in our experiments. The energy of the low-level air and the convection is lower/weaker over the Indian subcontinent in the full Tibetan Plateau experiment than that in the no-Tibetan Plateau experiment or the barrier only experiment, which is opposite to the barrier "blocking" hypothesis. Instead, there is a similar candle-like latent heating in the middle troposphere along the south edge of the Tibetan Plateau in both the full Tibetan Plateau and the barrier experiments, whereas this "candle heating" disappears in the no-Tibetan Plateau experiment. We propose that this candle heating is the key to understand the mechanisms of the Tibetan Plateau on the South Asian monsoon. Future studies are needed to check the source of the "candle heating" and its effect on the Asian monsoon.

scholarly journals Quantifying snow-darkening and atmospheric radiative effects of black carbon and dust on the South-Asian Monsoon and hydrological cycle: Experiments using variable resolution CESM

2019 ◽  
Author(s):  
Stefan Rahimi ◽  
Xiaohong Liu ◽  
Chenglai Wu ◽  
William K. Lau ◽  
Hunter Brown ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Black Carbon ◽  
South Asian ◽  
Asian Monsoon ◽  
Hydrological Cycle ◽  
South Asian Monsoon ◽  
The Tibetan Plateau ◽  
The South ◽  
Variable Resolution ◽  
Absorbing Aerosols

Abstract. Black carbon (BC) and dust impart significant effects on the south-Asian monsoon (SAM), which is responsible for ~80 % of the region’s annual precipitation. This study implements a variable-resolution (VR) version of Community Earth System Model (CESM) to quantify the impacts of absorbing BC and dust on the SAM. This study focuses on the snow darkening effect (SDE), as well as how these aerosols interact with incoming and outgoing radiation to facilitate an atmospheric response (i.e., aerosol radiation interactions (ARI)). By running sensitivity experiments, the individual effects of SDE and ARI are quantified, and a theoretical framework is applied to assess these aerosols’ impacts on the SAM. It is found that ARI of absorbing aerosols warm the atmospheric column in a belt coincident with the May-June averaged location of the subtropical jet, bringing forth anomalous upper-tropospheric (lower-tropospheric) anticyclogenesis (cyclogenesis) and divergence (convergence). This anomalous arrangement in the mass fields brings forth enhanced rising vertical motion across south Asia and a stronger westerly low-level jet, the latter of which furnishes the Indian subcontinent with enhanced Arabian Gulf moisture. This leads to precipitation increases of +2 mm d−1 or more across much of northern India from May through August, with larger anomalies in the western Indian mountains and southern TP mountain ranges due to orographic and anabatic enhancement. Across the Tibetan Plateau foothills, SDE by BC aerosol drives large precipitation anomalies of >6 mm d−1, comparable to ARI of absorbing aerosols from April through August. Runoff changes accompany precipitation and Tibetan Plateau snow changes, which have consequences for south-Asian water resources.

scholarly journals Reexamining the barrier effect of the Tibetan Plateau on the South Asian summer monsoon

2014 ◽  
Vol 10 (3) ◽  
pp. 1269-1275 ◽  
Author(s):  
G.-S. Chen ◽  
Z. Liu ◽  
J. E. Kutzbach
Keyword(s):  
Tibetan Plateau ◽  
South Asian ◽  
Summer Monsoon ◽  
Asian Monsoon ◽  
Asian Summer Monsoon ◽  
Monsoon Circulation ◽  
The Tibetan Plateau ◽  
South Asian Summer Monsoon ◽  
The South ◽  
Monsoon System

Abstract. The Tibetan Plateau has been conventionally treated as an elevated heat source driving the Asian monsoon system, especially for the South Asian monsoon. Numerous model simulations with general circulation models (GCMs) support this hypothesis with the finding that the Asian monsoon system is weak or absent when all elevated topography is removed. A recent model simulation shows that the South Asian summer monsoon circulation is little affected with only the Himalayas (no-Tibetan Plateau) kept as a barrier, leading to a hypothesis of the barrier "blocking" mechanism of the Tibetan Plateau. In this paper, a new series of experiments are designed to reexamine this barrier effect. We find that with the barrier, the large-scale summer monsoon circulation over South Asia is simulated in general agreement with the full Tibetan Plateau, which is consistent with the previous finding. However, there remains significant differences in both wind and precipitation fields, suggesting a role for the full Tibetan Plateau as well. Moreover, the proposed barrier blocking mechanism is not found in our experiments. The energy of the low-level air and the convection are lower and weaker over the Indian subcontinent in the full Tibetan Plateau experiment than that in the no-Tibetan Plateau experiment or the barrier only experiment, which is in contrast to the barrier blocking hypothesis. Instead, there is a similar candle-like latent heating in the middle troposphere along the southern edge of the Tibetan Plateau in both the full Tibetan Plateau and the barrier experiments, whereas this "candle heating" disappears in the no-Tibetan Plateau experiment. We propose that this candle heating is the key to understanding the mechanisms of the Tibetan Plateau on the South Asian monsoon. Future studies are needed to check the source of the "candle heating" and its effect on the Asian monsoon.

Climate response of the south Asian monsoon system to West Asia, Tibetan Plateau and local dust emissions

2019 ◽  
Vol 53 (9-10) ◽  
pp. 6245-6264 ◽  
Author(s):  
Charu Singh ◽  
Dilip Ganguly ◽  
Puneet Sharma ◽  
Shiwansha Mishra
Keyword(s):  
Tibetan Plateau ◽  
South Asian ◽  
Asian Monsoon ◽  
South Asian Monsoon ◽  
Climate Response ◽  
The South ◽  
Dust Emissions ◽  
Monsoon System ◽  
Local Dust
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