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Volume 16, issue 3
Atmos. Chem. Phys., 16, 1849–1862, 2016
https://doi.org/10.5194/acp-16-1849-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 16, 1849–1862, 2016
https://doi.org/10.5194/acp-16-1849-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 17 Feb 2016

Research article | 17 Feb 2016

Drizzle formation in stratocumulus clouds: effects of turbulent mixing

L. Magaritz-Ronen, M. Pinsky, and A. Khain L. Magaritz-Ronen et al.
  • Department of Atmospheric Sciences, The Hebrew University of Jerusalem, Israel

Abstract. The mechanism of drizzle formation in shallow stratocumulus clouds and the effect of turbulent mixing on this process are investigated. A Lagrangian–Eularian model of the cloud-topped boundary layer is used to simulate the cloud measured during flight RF07 of the DYCOMS-II field experiment. The model contains ~ 2000 air parcels that are advected in a turbulence-like velocity field. In the model all microphysical processes are described for each Lagrangian air volume, and turbulent mixing between the parcels is also taken into account. It was found that the first large drops form in air volumes that are closest to adiabatic and characterized by high humidity, extended residence near cloud top, and maximum values of liquid water content, allowing the formation of drops as a result of efficient collisions. The first large drops form near cloud top and initiate drizzle formation in the cloud. Drizzle is developed only when turbulent mixing of parcels is included in the model. Without mixing, the cloud structure is extremely inhomogeneous and the few large drops that do form in the cloud evaporate during their sedimentation. It was found that turbulent mixing can delay the process of drizzle initiation but is essential for the further development of drizzle in the cloud.

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The mechanism of drizzle formation in shallow stratocumulus clouds and the effect of turbulent mixing on this process are investigated using a Lagrangian-Eularian model of the cloud-topped boundary layer. It was found that first large drops form in volumes that are closest to adiabatic with extended residence near cloud top, and maximum values of LWC. Turbulent mixing was found able to delay the process of drizzle initiation but is essential for the further development of drizzle in the cloud.
The mechanism of drizzle formation in shallow stratocumulus clouds and the effect of turbulent...
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