Parameterization Schemes

Catalog description

Parameterization is the process by which important physical processes that cannot be resolved explicitly in a numerical model are represented. Examples include the transfer of shortwave radiation through the atmosphere, and the formation of cloud droplets, both of which occur on the molecular scale. As numerical models have grid spacing of hundreds of meters, molecular processes are not resolved explicitly in current models and so must be parameterized. A parameterization scheme is a representation of our understanding of the physical process as related to the available model variables, such that one can estimate how the behaviors of these important sub-grid physical processes influence the available model variables. In this way, sub-grid scale physical processes are included in models even when they cannot be explicitly represented. The most common parameterization schemes used in numerical models of the atmosphere will be discussed, including land and ocean surface, planetary boundary layer, convection, microphysics, radiation, cloud cover, and orographic drag. Emphasis is placed upon understanding the basic approaches to parameterization and how the differences in approaches influence the resulting behaviors.