scholarly journals Relative importance of greenhouse gases, sulfate, organic carbon, and black carbon aerosol for South Asian monsoon rainfall changes

2020 ◽  
Author(s):  
Daniel M Westervelt ◽  
Yujia You ◽  
Xiaoqiong Li ◽  
Mingfang Ting ◽  
Dong Eun Lee ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Greenhouse Gases ◽  
Black Carbon ◽  
South Asian ◽  
Asian Monsoon ◽  
Monsoon Rainfall ◽  
South Asian Monsoon ◽  
Relative Importance ◽  
Black Carbon Aerosol

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 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 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.

Disentangling sea-surface temperature and anthropogenic aerosol influences on recent trends in South Asian monsoon rainfall

2018 ◽  
Vol 52 (3-4) ◽  
pp. 2287-2302 ◽  
Author(s):  
Nitin Patil ◽  
Chandra Venkataraman ◽  
Kaushik Muduchuru ◽  
Subimal Ghosh ◽  
Arpita Mondal
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
South Asian ◽  
Asian Monsoon ◽  
Monsoon Rainfall ◽  
Sea Surface ◽  
South Asian Monsoon ◽  
Anthropogenic Aerosol ◽  
Recent Trends

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

2015 ◽  
Vol 15 (11) ◽  
pp. 6367-6378 ◽  
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 24 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.

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