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 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.

Investigating the sensitivity of the onset and withdrawal of the south Asian summer monsoon system to changes in anthropogenic emissions using a climate model

2020 ◽  
Author(s):  
Shiwansha Mishra ◽  
Dilip Ganguly ◽  
Puneet Sharma
Keyword(s):  
South Asian ◽  
Summer Monsoon ◽  
Climate Model ◽  
Asian Summer Monsoon ◽  
Anthropogenic Emissions ◽  
South Asian Summer Monsoon ◽  
The South ◽  
Monsoon System ◽  
Asian Summer ◽  
The Impact

<p>While the monsoon onset is recognized as a rapid, substantial, and sustained increase in rainfall over large parts of south Asia, the withdrawal marks the return to dry conditions. Normally, the south Asian summer monsoon onset occurs around 1<sup>st</sup> June over extreme south of peninsular India, which gradually advances to extreme northwest of India by around 15<sup>th</sup> July. The withdrawal starts from northwest India from around 1st September and from extreme south peninsular India by around 30th September. The determinations of the onset and withdrawal dates of monsoon have great economic significance for this region as they influence many agriculture and water resource management decisions in one of the most highly populated regions of the world. Several studies involving global model simulations have shown that changing aerosol emissions could result in significant changes in the seasonal mean precipitation distribution over India. A few studies also show that presence of absorbing aerosols in the foothills of Himalayas and over the Tibetan plateau could increase the moisture convergence over India thereby causing an advancement and intensification of the monsoon precipitation. However, most of the previous studies, which investigated the impact of anthropogenic emissions on the monsoon, are limited to understanding the impact of various emission changes on the seasonal mean monsoon characteristics. In the present study, we try to understand the sensitivity of the onset and withdrawal period of the south Asian summer monsoon system to changes in anthropogenic emissions using a climate model (CESM1.2). We diagnose the onset and withdrawal of the south Asian monsoon by analyzing the variability in vertically integrated moisture transport (VIMT) over the south Asian region and following the definition of hydrologic onset and withdrawal index (HOWI) defined by Fasullo et al. (2002). We examined the effect of changing emissions anthropogenic aerosol, greenhouse gases and both on the onset and withdrawal of the south Asian summer monsoon system. Our preliminary results suggest that increases in the emissions of aerosols and greenhouse gases from anthropogenic sources from pre-industrial to present day could possibly result in significant delay in the onset and advancement in withdrawal of the south Asian summer monsoon system thereby shortening the length of the monsoon season. More results with greater detail will be presented.</p>

scholarly journals Effect of Indian Ocean SST on Tibetan Plateau Precipitation in the Early Rainy Season

2017 ◽  
Vol 30 (22) ◽  
pp. 8973-8985 ◽  
Author(s):  
Xiaoyang Chen ◽  
Qinglong You
Keyword(s):  
Indian Ocean ◽  
Tibetan Plateau ◽  
South Asia ◽  
Rainy Season ◽  
Asian Summer Monsoon ◽  
Phase Relationship ◽  
The Tibetan Plateau ◽  
South Asian Summer Monsoon ◽  
The South ◽  
Monsoon System

The onset of the South Asian summer monsoon (SASM) indicates the beginning of the rainy season in the South Asia region. It is not only critical for the local agriculture and animal husbandry but also important for water and life security. Precipitation in the early rainy season (May) increases rapidly and has a large interannual variability, especially in the Tibetan Plateau (TP) region. One of the starting mechanisms of the monsoon system is the land–sea thermal contrast (LSTC) between the Indian Ocean (IO) and South Asia region. Therefore, the IO can be considered as a crucial factor for the intensity of the monsoon system, as well as the TP precipitation. In this study, the relationships between IO sea surface temperature (SST) and TP precipitation on the interannual time scale are investigated. Correlation maps show that IO SST variability contains a portion that is independent from the tropical Pacific Ocean SST and is negatively correlated with the TP precipitation. Here the authors define an LSTC index to determine the thermal condition over the IO and South Asia region. The SASM reveals an out-of-phase relationship with LSTC between land and ocean, which means it would be suppressed by the enhanced LSTC. The daily data are used to further analyze the relationship between the SASM and TP precipitation in detail. Results show that the anomalous TP precipitation in May is mainly caused by the Bay of Bengal monsoon and that the Indian monsoon is responsible for the TP precipitation in June. More specifically, warmer SST enlarges the LSTC between the IO and South Asia region. The SASM is weaker than the mean state, resulting in less precipitation over the TP. In negative years the opposite occurs.

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