Numerical simulation of cloud-clear air interfacial mixing: Effects on cloud microphysics

AMS Citation:
Andrejczuk, M., W. W. Grabowski, S. P. Malinowski, and P. Smolarkiewicz, 2006: Numerical simulation of cloud-clear air interfacial mixing: Effects on cloud microphysics. Journal of the Atmospheric Sciences, 63, 3204-3225, doi:10.1175/JAS3813.1.
Resource Type:article
Title:Numerical simulation of cloud-clear air interfacial mixing: Effects on cloud microphysics
Abstract: This paper extends the previously published numerical study of Andrejczuk et al. on microscale cloud-clear air mixing. Herein, the primary interest is on microphysical transformations. First, a convergence study is performed--with well-resolved direct numerical simulation of the interfacial mixing in the limit--to optimize the design of a large series of simulations with varying physical parameters. The principal result is that all conclusions drawn from earlier low-resolution (Δx = 10⁻² m) simulations are corroborated by the high-resolution (Δx = 0.25 × 10⁻² m) calculations, including the development of turbulent kinetic energy (TKE) and the evolution of microphysical properties. This justifies the use of low resolution in a large set of sensitivity simulations, where microphysical transformations are investigated in response to variations of the initial volume fraction of cloudy air, TKE input, liquid water mixing ratio in cloudy filaments, relative humidity (RH) of clear air, and size of cloud droplets. The simulations demonstrate that regardless of the initial conditions the evolutions of the number of cloud droplets and the mean volume radius follow a universal path dictated by the TKE input, RH of clear air filaments, and the mean size of cloud droplets. The resulting evolution path only weakly depends on the progress of the homogenization. This is an important conclusion because it implies that a relatively simple rule can be developed for representing the droplet-spectrum evolution in cloud models that apply parameterized microphysics. For the low-TKE input, when most of the TKE is generated by droplet evaporation during mixing and homogenization, an inhomogeneous scenario is observed with approximately equal changes in the dimensionless droplet number and mean volume radius cubed. Consistent with elementary scale analysis, higher-TKE inputs, higher RH of cloud-free filaments, and larger cloud droplets enhance the homogeneity of mixing. These results are discussed in the context of observations of entrainment and mixing in natural clouds.
Subject(s):Cloud microphysics, Mesoscale process
Peer Review:Refereed
Copyright Information:Copyright 2006 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be "fair use" under Section 107 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Law (17 USC, as revised by P.L. 94-553) does not require the Society's permission. Republication, systematic reproduction, posting in electronic form on servers, or other uses of this material, except as exempted by the above statements, requires written permission or license from the AMS. Additional details are provided in the AMS Copyright Policies, available from the AMS at 617-227-2425 or Permission to place a copy of this work on this server has been provided by the AMS. The AMS does not guarantee that the copy provided here is an accurate copy of the published work.
OpenSky citable URL: ark:/85065/d7pr7w8x
Publisher's Version: 10.1175/JAS3813.1
  • Miroslaw Andrejczuk - NCAR/UCAR
  • Wojciech Grabowski - NCAR/UCAR
  • Szymon Malinowski
  • Piotr Smolarkiewicz - NCAR/UCAR
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