scholarly journals Understanding land surface response to changing South Asian monsoon in a warming climate

2015 ◽  
Vol 6 (2) ◽  
pp. 569-582 ◽  
Author(s):  
M. V. S Ramarao ◽  
R. Krishnan ◽  
J. Sanjay ◽  
T. P. Sabin
Keyword(s):  
Climate Change ◽  
South Asian ◽  
Land Surface ◽  
Asian Monsoon ◽  
Global Climate ◽  
Monsoon Circulation ◽  
South Asian Monsoon ◽  
Monsoon Precipitation ◽  
Surface Response ◽  
Regional Land

Abstract. Recent studies have drawn attention to a significant weakening trend of the South Asian monsoon circulation and an associated decrease in regional rainfall during the last few decades. While surface temperatures over the region have steadily risen during this period, most of the CMIP (Coupled Model Intercomparison Project) global climate models have difficulties in capturing the observed decrease of monsoon precipitation, thus limiting our understanding of the regional land surface response to monsoonal changes. This problem is investigated by performing two long-term simulation experiments, with and without anthropogenic forcing, using a variable resolution global climate model having high-resolution zooming over the South Asian region. The present results indicate that anthropogenic effects have considerably influenced the recent weakening of the monsoon circulation and decline of precipitation. It is seen that the simulated increase of surface temperature over the Indian region during the post-1950s is accompanied by a significant decrease of monsoon precipitation and soil moisture. Our analysis further reveals that the land surface response to decrease of soil moisture is associated with significant reduction in evapotranspiration over the Indian land region. A future projection, based on the representative concentration pathway 4.5 (RCP4.5) scenario of the Intergovernmental Panel on Climate Change (IPCC), using the same high-resolution model indicates the possibility for detecting the summer-time soil drying signal over the Indian region during the 21st century in response to climate change. Given that these monsoon hydrological changes have profound socio-economic implications the present findings provide deeper insights and enhance our understanding of the regional land surface response to the changing South Asian monsoon. While this study is based on a single model realization, it is highly desirable to have multiple realizations to establish the robustness of the results.

scholarly journals Understanding land surface response to changing South Asian monsoon in a warming climate

2015 ◽  
Vol 6 (1) ◽  
pp. 943-977 ◽  
Author(s):  
M. V. S. Ramarao ◽  
R. Krishnan ◽  
J. Sanjay ◽  
T. P. Sabin
Keyword(s):  
High Resolution ◽  
South Asian ◽  
Land Surface ◽  
Asian Monsoon ◽  
Global Climate ◽  
Monsoon Circulation ◽  
South Asian Monsoon ◽  
Monsoon Precipitation ◽  
Surface Response ◽  
Regional Land

Abstract. Recent studies have drawn attention to a significant weakening trend of the South Asian monsoon circulation and an associated decrease in regional rainfall during the last few decades. While surface temperatures over the region have steadily risen during this period, most of the CMIP (Coupled Model Intercomparison Project) global climate models have difficulties in capturing the observed decrease of monsoon precipitation, thus limiting our understanding of the regional land surface response to monsoonal changes. This problem is investigated by performing two long-term simulation experiments, with and without anthropogenic forcing, using a variable resolution global climate model having high-resolution zooming over the South Asian region. The present results indicate that anthropogenic effects have considerably influenced the recent weakening of the monsoon circulation and decline of precipitation. It is seen that the simulated increase of surface temperature over the Indian region during the post-1950s is accompanied by a significant decrease of monsoon precipitation and soil moisture. Our analysis further reveals that the land surface response to decrease of soil moisture is associated with significant reduction in evapotranspiration over the Indian land region. A future projection, based on the representative concentration pathway 4.5 (RCP4.5) scenario of the Intergovernmental panel on Climate Change (IPCC), using the same high-resolution model indicates the possibility for detecting the summer-time soil drying signal over the Indian region during the 21st century, in response to climate change. While these monsoon hydrological changes have profound socioeconomic implications, the robustness of the high-resolution simulations provides deeper insights and enhances our understanding of the regional land surface response to the changing South Asian monsoon.

Phased evolution and variation of the South Asian monsoon, and resulting weathering and surface erosion in the Himalaya–Karakoram Mountains, since late Pliocene time using data from Arabian Sea core

2020 ◽  
Vol 157 (6) ◽  
pp. 864-878 ◽  
Author(s):  
Huayu Lu ◽  
Ruixuan Liu ◽  
Linhai Cheng ◽  
Han Feng ◽  
Hanzhi Zhang ◽  
...  
Keyword(s):  
South Asian ◽  
Arabian Sea ◽  
Asian Monsoon ◽  
Monsoon Rainfall ◽  
South Asian Monsoon ◽  
Monsoon Precipitation ◽  
Late Pliocene ◽  
Weathering Intensity ◽  
Karakoram Mountains ◽  
The Himalaya

AbstractWe investigate the phased evolution and variation of the South Asian monsoon and resulting weathering intensity and physical erosion in the Himalaya–Karakoram Mountains since late Pliocene time (c. 3.4 Ma) using a comprehensive approach. Neodymium and strontium isotopic compositions and single-grain zircon U–Pb age spectra reveal the sources of the deposits in the east Arabian Sea, and show a combination of sources from the Himalaya and the Karakoram–Kohistan–Ladakh Mountains, with sediments from the Indian Peninsula such as the Deccan Traps or Craton. We interpret shifts in the sediment sources to have been forced by sea-level changes that correlate with South Asian monsoon rainfall variation since late Pliocene time. We collected 908 samples from the International Ocean Discovery Program Hole U1456A, which was drilled in the east Arabian Sea. Time series of hematite content and grain size of the sediments were examined downcore. We found South Asian monsoon precipitation and weathering intensity experienced three phases from late Pliocene time. Lower monsoon precipitation, with a lower variability and strong weathering intensity, occurred during 3.4–2.4 Ma; an increased and more variable South Asian monsoon rainfall, along with strengthened but fluctuating weathering intensity, occurred at 1.8–1.1 Ma; and a reduced rainfall with lower South Asian monsoon precipitation variability and moderate weathering intensity marked the period 1.1–0.1 Ma. Maximum entropy spectral analysis and wavelet transform show that there were orbital-dominated cycles of periods c. 100 and c. 41 ka in these proxy-based time series. We propose that the monsoon, sea level, global temperature and insolation together forced the weathering and erosion in SW Asia.

scholarly journals South Asian monsoon climate change and radiocarbon in the Arabian Sea during early and middle Holocene

2002 ◽  
Vol 17 (4) ◽  
pp. 15-1-15-12 ◽  
Author(s):  
Michael Staubwasser ◽  
Frank Sirocko ◽  
Pieter M. Grootes ◽  
Helmut Erlenkeuser
Keyword(s):  
Climate Change ◽  
South Asian ◽  
Arabian Sea ◽  
Asian Monsoon ◽  
South Asian Monsoon ◽  
Monsoon Climate ◽  
Middle Holocene ◽  
Early And Middle Holocene

Combined effects of anthropogenic aerosols and global warming on the South Asian Monsoon

2020 ◽  
Author(s):  
Ayantika Dey Choudhury ◽  
Krishnan Raghavan ◽  
Manmeet Singh ◽  
Swapna Panickal ◽  
Sandeep Narayansetti ◽  
...  
Keyword(s):  
Global Warming ◽  
South Asian ◽  
Large Scale ◽  
Asian Monsoon ◽  
Monsoon Circulation ◽  
South Asian Monsoon ◽  
Combined Effects ◽  
The South ◽  
Anthropogenic Aerosols ◽  
Aerosol Forcing

<p>The South Asian monsoon (SAM) precipitation has been generally regarded to exhibit contrasting responses to greenhouse gas (GHG) and anthropogenic aerosol forcing, although it is not adequately clear as to how it might respond to the combined influence of GHG and aerosol forcing.  The present study examines the individual and combined effects of global warming and anthropogenic aerosols on the SAM based on a suite of numerical experiments conducted using the IITM Earth System Model version2 (IITM-ESMv2). Four sets of 50-year model integrations are performed using IITM-ESMv2 with different anthropogenic forcings 1) Pre-Industrial control, 2) anthropogenic aerosols of 2005 3) CO2 concentrations of 2005 4) anthropogenic aerosols and CO2 of 2005. In the experiment with the elevated CO2 level of 2005, an intensification of SAM precipitation and strengthening of large-scale monsoon cross-equatorial flow is noted relative to the PI-CTL run. In contrast, the experiment with elevated anthropogenic aerosols of 2005 shows a decrease of SAM precipitation and weakening of monsoon circulation relative to the PI-CTL run. A striking result emerging from this study is the strong suppression of SAM precipitation, pronounced weakening of the monsoon circulation and suppression of organized convection in response to the combined radiative effects of elevated CO2 and anthropogenic aerosols relative to the PI-CTL run. By diagnosing the model simulations it is noted that the radiative effects in the combined forcing experiment lead to a pronounced summer-time cooling of the NH as compared to the equatorial and southern oceans which are predominantly influenced by global warming, thereby creating a north-south differential radiative forcing over the Indian longitudes.  Additionally, the influence of absorbing aerosols over South and East Asia creates a surface radiation deficit over the region, stabilizes the lower troposphere, slows down the monsoon winds and reduces surface evaporation.  Although the anticyclones over the subtropical Indian Ocean intensify in the combined forcing experiment, the model simulation shows that much of the precipitation enhancement occurs to the south of the equator over the Indian Ocean whereas the moisture transport and convergence to the north of the equator is substantially reduced. Furthermore, the combined forcing experiment shows that anomalous large-scale descent over the subcontinent reinforces the suppression of organized convection giving rise to more intense breaks and weaker active spells in the southwest monsoon on sub-seasonal time-scales. This study hints that future decreases in NH aerosol emissions could potentially reverse the ongoing decreasing trend of the observed SAM precipitation since 1950s in a purely global warming environment.</p>

scholarly journals High resolution simulation of the South Asian monsoon using a variable resolution global climate model

2013 ◽  
Vol 41 (1) ◽  
pp. 173-194 ◽  
Author(s):  
T. P Sabin ◽  
R. Krishnan ◽  
Josefine Ghattas ◽  
Sebastien Denvil ◽  
Jean-Louis Dufresne ◽  
...  
Keyword(s):  
High Resolution ◽  
South Asian ◽  
Asian Monsoon ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
South Asian Monsoon ◽  
The South ◽  
Variable Resolution ◽  
Resolution Simulation

scholarly journals South Asian monsoon precipitation in CMIP5: a link between inter-model spread and the representations of tropical convection

2018 ◽  
Vol 52 (1-2) ◽  
pp. 1049-1061 ◽  
Author(s):  
Samson Hagos ◽  
L. Ruby Leung ◽  
Moetasim Ashfaq ◽  
Karthik Balaguru
Keyword(s):  
South Asian ◽  
Asian Monsoon ◽  
Tropical Convection ◽  
South Asian Monsoon ◽  
Monsoon Precipitation

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 Upper-Tropospheric Forcing on Late July Monsoon Transition in East Asia and the Western North Pacific

2012 ◽  
Vol 25 (11) ◽  
pp. 3929-3941 ◽  
Author(s):  
Chi-Hua Wu ◽  
Ming-Dah Chou
Keyword(s):  
East Asia ◽  
South Asian ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Asian Monsoon ◽  
Monsoon Circulation ◽  
South Asian Monsoon ◽  
The South ◽  
The North

By investigating the large-scale circulation in the upper troposphere, it is demonstrated that the rapid late July summer monsoon transition in the East Asia and western North Pacific (EA-WNP) is associated with a weakened westerly at the exit of the East Asian jet stream (EAJS). Even in a normally stable atmosphere under the influence of the North Pacific (NP) high in late July, convection rapidly develops over the midoceanic region of the western NP (15°–25°N, 150°–170°E). Prior to the rapid transition, the EAJS weakens and shifts northward, which induces a series of changes in downstream regions; the northeastern stretch of the Asian high weakens, upper-tropospheric divergence in the region southwest of the mid-NP trough increases, and convection is enhanced. At the monsoon transition, upper-level high potential vorticity intrudes southward and westward, convection expand from the mid NP westward to cover the entire subtropical western NP, the lower-tropospheric monsoon trough deepens, surface southwesterly flow strengthens, and the western stretch of the NP high shifts northward ~10° latitude to the south of Japan. This series of changes indicates that the EA-WNP late July monsoon transition is initiated from changes in the upper-tropospheric circulation via the weakening of the EAJS south of ~45°N. The weakening of the EAJS south of ~45°N is related to a reduced gradient of the geopotential height on the northern flank of the Asian high, which is related to the massive inland heating and weakening of the South Asian monsoon circulation. The exact timing of the monsoon onset might be tied to the hypothesized “Silk Road pattern” and/or a strong weakening of the South Asian monsoon circulation.

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