Lipps, F. B., 1977: A study of turbulence parameterization in a cloud model. Journal of the Atmospheric Sciences, 34 (11), 1751-1772.
Abstract: A diagnostic second-order turbulence parameterization has been incorporated
into a shallow anelastic three-dimensional numerical cloud model. The turbulence
closure scheme for the subgrid-scale motions includes the effects of buoyancy,
condensation and liquid water drag. This model has been used to study trade
wind cumuli which are roughly 1200 m thick. The simulated cloud has many
features in common with observed clouds (Malkus, 1954); however, the observed
clouds are made up of several thermal elements instead of one as in the
numerical simulation, and they persist over a much longer time period.
When comparing the present model with another using deformation eddy viscosity,
the following results are obtained: 1) The deformation model has a larger
smoothing effect on the horizontally averaged potential temperature and
water vapor mixing ratio. 2) Early in the cloud's development, the subgrid-scale
kinetic energy is larger than the computed-scale kinetic energy. At the
mature stage, the subgrid-scale energy is about one-half to three-quarters
the magnitude of the computed-scale kinetic energy. In the deformation model
the subgrid-scale turbulence is less, especially in the early stages of
the cloud's history. 3) It is found that buoyancy effects can be dropped
from the Reynold's stress equation without significant loss of accuracy.
The results of both models are highly sensitive to changes of external
parameters. This type of sensitivity is either a characteristic of clouds
in general, or is a special property of the present models.