Improved prediction of the impact of shallow cumuli using WRF
Authors
Larry Berg — Pacific Northwest National Laboratory
William I. Gustafson — Pacific Northwest National Laboratory
Evgueni Kassianov — Pacific Northwest National Laboratory
Description
Recently, the Weather Research and Forecasting (WRF) model has been modified to improve the representation of shallow cumuli. Changes have been made to both the WRF cumulus and radiation parameterizations. In the cumulus parameterization, the trigger function applied in the standard Kain-Fritsch scheme has been improved to account for the sub-grid variability of temperature and humidity within the boundary layer. In the radiation parameterization, the cloud fraction computed in the cumulus parameterization is used to determine the radiative fluxes, rather than the standard cloud fraction formulation that is based on the grid box relative humidity. These changes improve the treatment of the radiative impacts of shallow convective clouds. Together, these modifications improve the prediction of shallow cumulus convection and the surface cloud effect, as is shown for three case studies that use data from the ARM Southern Great Plains site.
