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.

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.

The South Asia Monsoon Break Promotes Grass Growth on the Tibetan Plateau

2021 ◽  
Author(s):  
Yanghang Ren ◽  
Kun Yang ◽  
Han Wang
Keyword(s):  
Soil Moisture ◽  
Tibetan Plateau ◽  
Solar Radiation ◽  
Climate Variability ◽  
South Asia ◽  
The Tibetan Plateau ◽  
The South ◽  
Central Eastern ◽  
Grass Growth ◽  
The Impact

<p>As region that is highly sensitive to global climate change, the Tibetan Plateau (TP) experiences an intra-seasonal soil water deficient due to the reduced precipitation during the South Asia monsoon (SAM) break. Few studies have investigated the impact of the SAM break on TP ecological processes, although a number of studies have explored the effects of inter-annual and decadal climate variability. In this study, the response of vegetation activity to the SAM break was investigated. The data used are: (1) soil moisture from in situ, satellite remote sensing and data assimilation; and (2) the Normalized Difference Vegetation Index (NDVI) and Solar-Induced chlorophyll Fluorescence (SIF). We found that in the region impacted by SAM break, which is distributed in the central-eastern part of TP, photosynthesis become more active during the SAM break. And temporal variability in the photosynthesis of this region is controlled mainly by solar radiation variability and has little sensitivity to soil moisture. We adopted a diagnostic process-based modeling approach to examine the causes of enhanced plant activity during the SAM break on the central-eastern TP. Our analysis indicates that active photosynthetic behavior in the reduced precipitation is stimulated by increases in solar radiation absorbed and temperature. This study highlights the importance of sub-seasonal climate variability for characterizing the relationship between vegetation and climate.</p>

Drying Tendency over the Southern Tibetan Plateau in Recent Past Decades

2020 ◽  
Author(s):  
Ziqian Wang ◽  
Song Yang ◽  
Anmin Duan
Keyword(s):  
Tibetan Plateau ◽  
Asian Summer Monsoon ◽  
Wave Train ◽  
Dynamic Change ◽  
Internal Variability ◽  
The Tibetan Plateau ◽  
Southern Slope ◽  
South Asian Summer Monsoon ◽  
Budget Analysis ◽  
Upper Level

<p>The Tibetan Plateau (TP) exerts a significant impact on the weather and climate over many places of the world through both mechanical and thermal-dynamical effects. In summer, the major rainfall of the TP occurs over the southern slope, and the associated atmospheric latent heating dominates the total diabatic heating of TP. Then the variation of summer rainfall can directly regulate the TP’s thermal effects. On the other hand, the rainfall center over the southern slope is corresponding with the northern branch of South Asian summer monsoon, which is important to the agricultural productivity and economic stability along the Ganges River with dense population. This study shows that there existed a drying tendency over the southern TP (STP) in the rainy season of recent decades. A moisture budget analysis indicates that the dynamic change in vertical moisture advection is the dominant contributor to the drying trend, which is associated with the weakened upward motion over the STP. The changes in dynamic process over STP are induced by the northward shift of the subtropical westerly jet, whose northward shift reduces the upper-level anticyclone over STP and weakens the upper-level divergence, leading to a trend of vertical sinking motion. Furthermore, the northward shift of the jet is mainly attributed to the internal variability of the atmosphere, characterized by an upper-level circum-global wave train. The influence of atmospheric internal variability is demonstrated by the CESM Large Ensemble Project data.</p>

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