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

Journal Article · 26 September 2019 · Atmospheric Chemistry and Physics (Online)

DOI: https://doi.org/10.5194/acp-19-12025-2019 · OSTI ID:1633534

Rahimi, Stefan ^[1]; Liu, Xiaohong ^[1]; Wu, Chenglai  ^[2]; Lau, William K. ^[3]; Brown, Hunter ^[1]; Wu, Mingxuan  ^[1]; Qian, Yun  ^[4]

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1. Univ. of Wyoming, Laramie, WY (United States)
2. Univ. of Wyoming, Laramie, WY (United States); Chinese Academy of Sciences (CAS), Beijing (China)
3. Univ. of Maryland, College Park, MD (United States)
4. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

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 the Community Earth System Model (CESM) to quantify two radiative effects of absorbing BC and dust on the SAM. Specifically, 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, ARIs). 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 ARIs of absorbing aerosols warm the atmospheric column in a belt coincident with the May–June averaged locationof 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. Precipitation increases of 2 mm d–1 or more (a 60 % increase in June) result across much of northern India from May through August, with larger anomalies (+5 to +10 mm d–1) in the western Indian mountains and southern Tibetan Plateau (TP) mountain ranges due to orographic and an abatic enhancement. Across the Tibetan Plateau foothills, SDE by BC aerosols drives large precipitation anomalies of > 6 mm d–1(a 21%–26 % increase in May and June), comparable to ARI of absorbing aerosols from April through August. Runoff changes accompany BC SDE-induced snow changes across Tibet, while runoff changes across India result predominantly from dust ARI. Finally, there are large differences in the simulated SDE between the VR and traditional 1° simulations, the latter of which simulates a much stronger SDE and more effectively modifies the regional circulation.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: National Science Foundation of China; USDOE
• Grant/Contract Number: AC05-76RL01830
• OSTI ID: 1633534
• Report Number(s): PNNL-SA--148781
• Journal Information: Atmospheric Chemistry and Physics (Online), Journal Name: Atmospheric Chemistry and Physics (Online) Journal Issue: 18 Vol. 19; ISSN 1680-7324
• Publisher: European Geosciences UnionCopyright Statement
• Country of Publication: United States
• Language: English