Turbulence In Cumulus Clouds

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Abstract
The nature of turbulence in small cumuli is explored in a time-dependent model of moist non-precipitating convection. The problem is solved in a two-dimensional slab-symmetric geometry, but the turbulence is taken to be three-dimensional. Transport equations for the Reynolds stress and energy decay rate describe all scales of turbulence and hence no “seeding” of grid-resolvable scales with a random field is required. Results show the calculated turbulence to be highly anisotropic and in- homogeneous. Most of the turbulent energy resides in the vertical component of the Reynolds stress near cloud top, Consequently, vertical mixing is expected to be much more important than horizontal, in agreement with some recent experimental data. Abstract The nature of turbulence in small cumuli is explored in a time-dependent model of moist non-precipitating convection. The problem is solved in a two-dimensional slab-symmetric geometry, but the turbulence is taken to be three-dimensional. Transport equations for the Reynolds stress and energy decay rate describe all scales of turbulence and hence no “seeding” of grid-resolvable scales with a random field is required. Results show the calculated turbulence to be highly anisotropic and in- homogeneous. Most of the turbulent energy resides in the vertical component of the Reynolds stress near cloud top, Consequently, vertical mixing is expected to be much more important than horizontal, in agreement with some recent experimental data.

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