Impacts of reducing scattering and absorbing aerosols on the temporal extent and intensity of South Asian summer monsoon and East Asian summer monsoon
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Published:2023-07-26
Issue:14
Volume:23
Page:8341-8368
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Fang ChenweiORCID, Haywood Jim M.ORCID, Liang Ju, Johnson Ben T.ORCID, Chen YingORCID, Zhu Bin
Abstract
Abstract. The vast majority of reductions in aerosol emissions are projected to take place in the near future; however, associated impacts on the large-scale
circulation over the populated Asian monsoon region remain uncertain. Using the state-of-the-art UK Earth System Model version 1 (UKESM1), this
study examines the response of the South Asian summer monsoon and East Asian summer monsoon (SASM and EASM, respectively) to idealized reductions in anthropogenic emissions of
carbonaceous aerosols and SO2. The analysis focuses on changes in the monsoon temporal extent and intensity of precipitation following
decreases in either scattering (SCT) or absorbing (ABS) aerosols or decreases in both. For SCT, the combination of the early transition of land–sea
thermal contrast and sea level pressure gradient during the pre-monsoon season, together with the late transition in the post-monsoon season
associated with the tropospheric warming, advances the monsoon onset but delays its withdrawal, which leads to an extension of the summer rainy
season across South Asia and East Asia. The northward shift of the upper-tropospheric Asian jet forced by the SCT reduction causes the anomalous
convergence of tropospheric moisture and low-level ascent over northern India and eastern China. The intensification of the South Asian high (SAH)
due to the warming over land also contributes to the dynamic instability over Asia. These changes enhance the rainy season of these regions in
boreal summer. Reductions in absorbing aerosol act in the opposite sense, making the Asia's rainy season shorter and weaker due to the opposite
impacts on land–sea contrast, Asian jet displacement and SAH intensity. With reductions in both SCT and ABS aerosol together the monsoon systems
intensify, as the overall impact is dominated by aerosol scattering effects and results in the strengthening of monsoon precipitation and
850 hPa circulation. Although aerosol scattering and absorption play quite different roles in the radiation budget, their effects on the
monsoon precipitation seem to add almost linearly. Specifically, the patterns of monsoon-related large-scale responses from reducing both SCT and
ABS together are similar to the linear summation of separate effect of reducing SCT or ABS alone; this is despite the inherent nonlinearity of the
atmospheric systems. The opposing adjustments of Asian rainy season forced by the ABS and SCT aerosol emission reductions suggest that emission
controls that target factors like emissions of black carbon that warm the climate would have a different response to those that target overall aerosol
emissions.
Funder
National Natural Science Foundation of China Natural Environment Research Council
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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