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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/acp-2020-483
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-483
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  19 Jun 2020

19 Jun 2020

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A revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Distinct responses of Asian summer monsoon to black carbon aerosols and greenhouse gases

Xiaoning Xie1,2, Gunnar Myhre3, Xiaodong Liu1,4, Xinzhou Li1, Zhengguo Shi1, Hongli Wang5, Alf Kirkevåg6, Jean-Francois Lamarque7, Drew Shindell8, Toshihiko Takemura9, and Yangang Liu10 Xiaoning Xie et al.
  • 1SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China
  • 2CAS Center for Excellence in Quaternary Science and Global Change, Xi'an, China
  • 3Center for International Climate and Environmental Research, Oslo, Norway
  • 4University of Chinese Academy of Sciences, Beijing, China
  • 5School of Tourism and Hospitality Management, Shaanxi Radio and TV University, Xi'an, China
  • 6Norwegian Meteorological Institute, Oslo, Norway
  • 7National Center for Atmospheric Research, Boulder, USA
  • 8Nicholas School of the Environment, Duke University, Durham, USA
  • 9Climate Change Science Section, Kyushu University, Fukuoka, Japan
  • 10Environmental and Climate Sciences Department, Brookhaven National Laboratory, Upton, NY, USA

Abstract. Black carbon (BC) aerosols emitted from natural and anthropogenic sources induce positive radiative forcing and global warming, which in turn significantly affect the Asian summer monsoon (ASM). However, many aspects of the BC effect on ASM remain elusive and largely inconsistent among previous studies, which is strongly dependent on different low-level thermal feedbacks over the Asian continent and the surrounding ocean. This study examines the response of ASM to BC forcing in comparison with the effect of doubled greenhouse gases (GHGs) by analyzing the Precipitation Driver Response Model Intercomparison Project (PDRMIP) simulations under an extreme high BC level (10 times modern global BC emissions or concentrations, labeled by BC × 10) from nine global climate models (GCMs). The results show that although BC and GHGs both enhance the ASM precipitation minus evaporation (P–E) (a 13.6 % increase for BC forcing and 12.1 % for GHGs from the nine-model ensemble, respectively), there exists a much larger uncertainty in changes in ASM P–E induced by BC than by GHGs. The summer P–E is increased by 7.7 % to 15.3 % due to these two forcings over three sub-regions including East Asian, South Asian, and western North Pacific monsoon regions. Further analysis of moisture budget reveals distinct mechanisms controlling the increases in ASM P–E induced by BC and GHGs. The change in ASM P–E by BC is dominated by the dynamic effect due to the enhanced large-scale monsoon circulation, whereas the GHG-induced change is dominated by the thermodynamic effect through increasing atmospheric water vapor. Radiative forcing of BC significantly increases the upper-level atmospheric temperature over the Asian region to enhance the upper-level meridional land-sea thermal gradient (MLOTG), resulting in a northward shift of the upper-level subtropical westerly jet and an enhancement of the low-level monsoon circulation; whereas radiative forcing of GHGs significantly increases the tropical upper-level temperature, which reduces the upper-level MLOTG and suppresses the low-level monsoonal circulation. Hence, our results indicate a different mechanism of BC climate effects under the extreme high BC level, that BC forcing significantly enhances the upper-level atmospheric temperature over the Asian region, determining ASM changes, instead of low-level thermal feedbacks as indicated by previous studies.

Xiaoning Xie et al.

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Xiaoning Xie et al.

Xiaoning Xie et al.

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This study examines the response of ASM to BC forcing in comparison with the effect of doubled GHGs by analyzing PDRMIP simulations from nine GCMs. The results show that although BC and GHGs both enhance the ASM P–E. Further analysis of moisture budget reveals distinct mechanisms controlling the increases in ASM P–E induced by BC and GHGs. The change in ASM P–E by BC is dominated by the dynamic effect, whereas the GHG-induced change is dominated by the thermodynamic effect.
This study examines the response of ASM to BC forcing in comparison with the effect of doubled...
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