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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-2020-817
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-817
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  25 Aug 2020

25 Aug 2020

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This preprint is currently under review for the journal ACP.

Organized Variations in MBL Cloud Microphysical Properties Observed by Aircraft and Satellite and Simulated by Model

Dale M. Ward1, Xiquan Dong1, Baike Xi1, Peng Wu1, Xiaojian Zheng1, and Yuan Wang2,3 Dale M. Ward et al.
  • 1Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ, 85710, USA
  • 2Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, 15 CA 91125, USA
  • 3Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

Abstract. Marine boundary layer (MBL) clouds in subtropical regions strongly impact global energy balance, but complete understanding of the processes that control their microphysical properties remain elusive. We analyze aircraft in-situ measurements of MBL clouds for two selected cases from the ACE-ENA field campaign that contain mesoscale convective cells (MCCs) on the order of tens of kilometers embedded in the large-scale overcast cloud field. The aircraft flight tracks aligned with the MCC organization, such that vertically-stacked, horizontal flight legs alternated between sampling clouds along organized MCCs and sampling clouds between MCCs. This alignment is well-suited to study the distinctly different microphysical properties for the two cloud regimes. Clouds within organized MCCs had lower droplet concentrations, but larger droplet sizes and liquid water contents with enhanced drizzle relative to clouds between MCCs. While observed aerosol properties below these two cloud regimes are generally consistent with their corresponding cloud microphysical properties, preexisting organization of the aerosol field was probably not required in the development of the MCC organization. In contrast, the lower aerosol and CCN concentrations observed below the MCC cloud layer most likely developed from precipitation and coalescence scavenging. A cloud-resolving WRF model simulation with realistic large-scale forcing reproduces the MCC organization of the cloud field suggesting that updraft velocity is the key to explain the differences in cloud microphysics. Both observations and model simulations indicate that under moderate-heavy drizzling conditions, precipitation and coalescence scavenging dominates and drives spatial gradients of cloud droplets, aerosols and CCN concentrations rather than local sources.

Dale M. Ward et al.

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Dale M. Ward et al.

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Short summary
Marine boundary layer clouds in subtropical regions strongly impact global energy balance, but complete understanding of the processes that control their development remain elusive. We analyze aircraft in-situ measurements of clouds collected in a field campaign for cases that contain organized structures tens of kilometres in extent embedded within a larger overcast cloud field. Failure to account for these structures can lead to misrepresentation in models and satellite retrievals.
Marine boundary layer clouds in subtropical regions strongly impact global energy balance, but...
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