Effect of improved physical parameterizations on simulations of cloudiness and the Earth's radiation budget

Abstract

The development of a new version of the United Kingdom Meteorological Office 11‐layer atmospheric general circulation model is described, with particular emphasis on the prediction of the fractional cloud cover and of the Earth's Radiation Budget. Results are shown first from an integration of an earlier version with model‐predicted cloudiness. These demonstrate that there were serious shortcomings, particularly in the distribution of low cloud over the subtropical oceans. Analysis of this problem showed that it was due to systematic errors in the thermo dynamic structure of the marine boundary layer. Various changes to the model's physical parameterizations were made to remove these errors, including revisions to the convection scheme to treat more accurately the effects of shallow cumulus convection. The new version of the model produces simulations of the geographical distribution of the components of the Earth's Radiation Budget which are generally in good agreement with satellite measurements.