Prognostic clouds

From Glossary of Meteorology



prognostic clouds

A set of prognostic equations containing parameterizations of various cloud microphysics processes, governing the evolution of cloud water.

The term "prognostic clouds" is usually reserved for numerical models that predict weather and climate. Prognostic cloud schemes may differ as to the number of prognostic equations and parameterized microphysics processes (the sources and sinks of cloud water), and as to whether or not they advect cloud water. In current climate models, spectral size distributions of cloud water particles (and falling condensate) are almost always assumed, rather than predicted, and their (radiative) effective radii are specified. Most often, the cloud volume fraction is parameterized by diagnostic relationships, as in purely empirically based, diagnostic cloud parameterizations, but it can be prognostic. Key cloud radiative properties, such as cloud optical depth and emissivity, may be parameterized in terms of the prognostic cloud variables and the (radiative) effective radii of the cloud particles.


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