A Highly Resolved Regional Climate Model (IPRC-RegCM) and Its Simulation of the 1998 Severe Precipitation Event over China. Part I: Model Description and Verification of Simulation

Abstract

East Asia is a region with complex topography, land surface conditions, coastlines, and with large contribution from mesoscale phenomena, such as the mei-yu/baiu frontal systems and tropical storms. To study the regional climate in such a region, a highly resolved regional climate model (IPRC-RegCM) has been recently developed at the International Pacific Research Center (IPRC). The distinct features of this model include the direct feedback of cumulus detrained cloud ice and cloud water into the grid-resolved quantities; the effect of cloud buoyancy on turbulence production with mixed-ice phase clouds; an explicit coupling between the cloud microphysics and radiation via cloud properties; an explicit coupling between land surface and radiation via surface albedo, direct and diffuse radiation fluxes; and the effect of frictionally generated dissipative heating. The model is documented in detail and the performance of the model is demonstrated by its simulation of the 1998 severe flooding event over China, the worst one since 1955. With the use of the objective analysis of the European Centre for Medium-Range Weather Forecasts (ECMWF), which is available at 12-h intervals with a resolution of 2.5° ? 2.5°, as both the initial and lateral boundary conditions, the model was integrated from 26 April to 31 August 1998 with a resolution of 0.5° ? 0.5° covering the area 5°?45°N, 90°?140°E. The model simulated realistically not only the temporal evolution of the area-averaged precipitation and the monthly mean precipitation spatial pattern but also the daily precipitation intensity distribution. The model reproduced the monsoon circulations, in particular, two episodes of the intraseasonal oscillation events that are believed to be closely related to the unusual double mei-yu periods over the Yangtze River basin in 1998.