Development of a Second-Generation Regional Climate Model (RegCM2). Part II: Convective Processes and Assimilation of Lateral Boundary Conditions

In this paper we continue the description of a second-generation regional climate model (RegCM2) initiated in the companion paper by Giorgi et al. We first discuss the inclusion in the model of the cumulus cloud scheme developed by Grell (referred to as OCC). The sensitivity of summertime and wintertime results to different closures and parameter settings in the GCC scheme are examined in model simulations conducted over Europe. While wintertime precipitation is found to vary only slightly between the experiments, a wide range of results is found in the summer runs. The GCC scheme produces more rain than a Kuo-type scheme, responds strongly to variations in the surface energy and moisture fluxes, and performs best when used in conjunction with the most advanced physics processes of RegCM2. Modifications to the standard model relaxation boundary condition procedure, which allow smoother assimilation of driving lateral boundary data, are also discussed. Further testing of RegCM2, which is more physically comprehensive, about three times more computationally efficient, and more portable than the previous version of the model, is continuing.