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Numerical Simulation of Cloud–Clear Air Interfacial Mixing: Homogeneous versus Inhomogeneous Mixing

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  • 1 Los Alamos National Laboratory, Los Alamos, New Mexico
  • | 2 National Center for Atmospheric Research, Boulder, Colorado
  • | 3 University of Warsaw, Institute of Geophysics, Warsaw, Poland
  • | 4 National Center for Atmospheric Research, Boulder, Colorado
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Abstract

This note presents an analysis of several dozens of direct numerical simulations of the cloud–clear air mixing in a setup of decaying moist turbulence with bin microphysics. The goal is to assess the instantaneous relationship between the homogeneity of mixing and the ratio of the time scales of droplet evaporation and turbulent homogenization. Such a relationship is important for developing improved microphysical parameterizations for large-eddy simulation of clouds. The analysis suggests a robust relationship for the range of time scale ratios between 0.5 and 10. Outside this range, the scatter of numerical data is significant, with smaller and larger time scale ratios corresponding to mixing scenarios that approach the extremely inhomogeneous and homogeneous limits, respectively. This is consistent with the heuristic argument relating the homogeneity of mixing to the time scale ratio.

* Current affiliation: School of Earth and Environment, University of Leeds, Leeds, United Kingdom.

+ The National Center for Atmospheric Research is sponsored by the National Science Foundation.

Corresponding author address: Wojciech W. Grabowski, NCAR/MMM, P.O. Box 3000, Boulder, CO 80307–3000. Email: grabow@ncar.ucar.edu

Abstract

This note presents an analysis of several dozens of direct numerical simulations of the cloud–clear air mixing in a setup of decaying moist turbulence with bin microphysics. The goal is to assess the instantaneous relationship between the homogeneity of mixing and the ratio of the time scales of droplet evaporation and turbulent homogenization. Such a relationship is important for developing improved microphysical parameterizations for large-eddy simulation of clouds. The analysis suggests a robust relationship for the range of time scale ratios between 0.5 and 10. Outside this range, the scatter of numerical data is significant, with smaller and larger time scale ratios corresponding to mixing scenarios that approach the extremely inhomogeneous and homogeneous limits, respectively. This is consistent with the heuristic argument relating the homogeneity of mixing to the time scale ratio.

* Current affiliation: School of Earth and Environment, University of Leeds, Leeds, United Kingdom.

+ The National Center for Atmospheric Research is sponsored by the National Science Foundation.

Corresponding author address: Wojciech W. Grabowski, NCAR/MMM, P.O. Box 3000, Boulder, CO 80307–3000. Email: grabow@ncar.ucar.edu

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