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.

Characteristics of Precipitating Convective Systems in the South Asian Monsoon

2011 ◽  
Vol 12 (1) ◽  
pp. 3-26 ◽  
Author(s):  
Ulrike Romatschke ◽  
Robert A. Houze
Keyword(s):  
South Asian ◽  
Diurnal Cycle ◽  
Bay Of Bengal ◽  
Arabian Sea ◽  
Asian Monsoon ◽  
South Asian Monsoon ◽  
Western Himalayas ◽  
The South ◽  
Convective Systems ◽  
Large Systems

Abstract Eight years of Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) data show how convective systems of different types contribute to precipitation of the South Asian monsoon. The main factor determining the amount of precipitation coming from a specific system is its horizontal size. Convective intensity and/or number of embedded convective cells further enhance its precipitation production. The precipitation of the monsoon is concentrated in three mountainous regions: the Himalayas and coastal ranges of western India and Myanmar. Along the western Himalayas, precipitation falls mainly from small, but highly convective systems. Farther east along the foothills, systems are more stratiform. These small and medium systems form during the day, as the monsoon flow is forced upslope. Nighttime cooling leads to downslope flow and triggers medium-sized systems at lower elevations. At the mountainous western coasts of India and Myanmar, small and medium systems are present throughout the day, as an orographic response to the southwesterly flow, with a slight superimposed diurnal cycle. Medium systems are favored over the eastern parts of the Arabian Sea and large systems are favored over the Bay of Bengal when an enhanced midlevel cyclonic circulation occurs over the northern parts of these regions. The systems forming upstream of coastal mountains over the Bay of Bengal are larger than those over the Arabian Sea, probably because of the moister conditions over the bay. The large systems over the bay exhibit a pronounced diurnal cycle, with systems forming near midnight and maximizing in midday.

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

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 Impacts of 20th century aerosol emissions on the South Asian monsoon in the CMIP5 models

2014 ◽  
Vol 14 (22) ◽  
pp. 30639-30666 ◽  
Author(s):  
L. Guo ◽  
A. G. Turner ◽  
E. J. Highwood
Keyword(s):  
South Asian ◽  
Indirect Effects ◽  
Asian Monsoon ◽  
Monsoon Rainfall ◽  
Cmip5 Models ◽  
Asymmetric Distribution ◽  
South Asian Monsoon ◽  
The South ◽  
Aerosol Effects ◽  
Aerosol Emissions

Abstract. Comparison of single-forcing varieties of 20th century historical experiments in a subset of models from the Fifth Coupled Model Intercomparison Project (CMIP5) reveals that South Asian summer monsoon rainfall increases towards the present day in Greenhouse Gas (GHG)-only experiments with respect to pre-industrial levels, while it decreases in anthropogenic aerosol-only experiments. Comparison of these single-forcing experiments with the all-forcings historical experiment suggests aerosol emissions have dominated South Asian monsoon rainfall trends in recent decades, especially during the 1950s to 1970s. The variations in South Asian monsoon rainfall in these experiments follows approximately the time-evolution of inter-hemispheric temperature gradient over the same period, suggesting a contribution from the large-scale background state relating to the asymmetric distribution of aerosol emissions about the equator. By examining the twenty-five available all-forcings historical experiments, we show that models including aerosol indirect effects dominate the negative rainfall trend. Indeed, models including only the direct radiative effect of aerosol show an increase in monsoon rainfall, consistent with the dominance of increasing greenhouse gas emissions and planetary warming on monsoon rainfall in those models. For South Asia, reduced rainfall in the models with indirect effects is related to decreased evaporation at the land surface rather than from anomalies in horizontal moisture flux, suggesting the impact of indirect effects on local aerosol emissions. This is confirmed by examination of aerosol loading and cloud droplet number trends over the South Asia region. Thus while remote aerosols and their asymmetric distribution about the equator play a role in setting the inter-hemispheric temperature distribution on which the South Asian monsoon, as one of the global monsoons, operates, the addition of indirect aerosol effects acting on very local aerosol emissions also plays a role in declining monsoon rainfall. The disparity between the response of monsoon rainfall to increasing aerosol emissions in models containing direct aerosol effects only and those also containing indirect effects needs to be urgently investigated since the suggested future decline in Asian anthropogenic aerosol emissions inherent to the representative concentration pathways (RCPs) used for future climate projection may turn out to be optimistic. In addition, both groups of models show declining rainfall over China, also relating to local aerosol mechanisms. We hypothesize that aerosol emissions over China are large enough, in the CMIP5 models, to cause declining monsoon rainfall even in the absence of indirect aerosol effects. The same is not true for India.

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.

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