A Revised Prognostic Cloud Fraction Scheme in a Global Forecasting System

Abstract

n this study, a revised prognostic cloud fraction scheme for atmospheric models is proposed and its performance is evaluated with a diagnostic cloud fraction scheme. A revision is proposed through a direct linkage between hydrometeors in the cumulus parameterization scheme and the amount of predicted cloud fractions. Cloud fractions that are determined via the prognostic cloud fraction scheme appear to be more realistic than those determined via a diagnostic cloud fraction scheme when both are compared with satellite data. In a medium-range forecast test bed, the biases of large-scale features such as temperature, geopotential height, and mean sea level pressure are moderately reduced when the prognostic cloud fraction scheme is used.