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Discussion papers
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 29 Mar 2019

Submitted as: research article | 29 Mar 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).

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

Stefan Rahimi1, Xiaohong Liu1, Chenglai Wu1,2, William K. Lau3, Hunter Brown1, Mingxuan Wu1, and Yun Qian4 Stefan Rahimi et al.
  • 1Department of Atmospheric Science, University of Wyoming, 1000 E. University, 1000 E. University Ave. Laramie, WY 82071
  • 2International Center for Climate and Environment Sciences, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China 100029
  • 3Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, 20742
  • 4Atmospheric Sciences and Global Change, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352

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.

Stefan Rahimi et al.
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Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Stefan Rahimi et al.
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Publications Copernicus
Short summary
Light-absorbing particles impact the earth system in a variety of ways. They can warm the atmosphere by their very presence, or they can warm the atmosphere after they deposit on snow, warm it, and warm the overlying atmosphere. This paper focuses on these two processes as they pertain to Black Carbon and dust's impacts on the South-Asian Monsoon. It will be shown that these two aerosols have a significant effect on the monsoon.
Light-absorbing particles impact the earth system in a variety of ways. They can warm the...