Convective Parameterization for Mesoscale Models: The Fritsch-Chappell Scheme

Abstract

The Fritsch and Chappell (1980) (hereafter FC) convective parameterization scheme was developed to facilitate numerical simulations of mesoscale convective systems. Since simulation of these systems requires resolution of meso-β-scale features, the parameterization was designed for models with grid increments of about 10–30 km. Grid elements this small allow for a somewhat different approach to the convective parameterization problem from that used for simulations that employ much larger elements (e.g., the 100–500-km grid increments used in general circulation and global climate models). In particular, grid elements that span several hundred kilometers are large enough to contain entire mesoscale convective systems and therefore the effects of convectively generated stratiform clouds and mesoscale circulations must also be parameterized. In contrast, grid increments of about 20 km are sufficient to resolve the convectively generated mesoscale circulations and associated cloud regions so that the parameterization problem reduces to incorporating the effects of only the convective clouds. It is assumed that if the convective clouds are properly parameterized, the resolvable-scale governing system of equations will develop the appropriate mesoscale mass, heat, moisture, and momentum transports.