Tests of precipitation parameterizations available in latest version of NCAR regional climate model (RegCM) over continental United States

This paper presents a series of tests of resolvable scale precipitation and cumulus convection schemes available in the latest version of the NCAR reg ional climate model (RegCM). For resolvable scale precipitation we use a ne w simplified explicit moisture (SIMEX) scheme, while for cumulus convection , we test the mass-flux scheme of Grell [1993], the Kuo-type scheme of Anth es [1977], and the newly implemented scheme of Zhang and McFarlane [1995]. The period of simulation is 3 years long, from March 1993 to February 1996, and the domain covers the continental United States at 60 km resolution. W hen using the SIMEX and Grell schemes, the model shows the best performance , with generally good simulation of precipitation, surface air temperature, and large-scale circulations throughout the United States. Both averages a nd anomalies associated with individual seasons are well reproduced at the regional scale. Main model deficiences are an underestimate of cold season precipitation over the eastern United States and a displacement of the summ er precipitation maximum over the central plains. The Kuo scheme has a perf ormance more similar to that of the Grell scheme than that of the Zhang and McFarlane (ZMF) scheme. Use of the ZMF scheme yields a reasonably good sim ulation of regionally averaged precipitation, but deteriorates some aspect of the simulation such as the intensity of the summer low-level jet over th e central plains. We also present sensitivity tests to various parameters i n the schemes which can be of guidance to the model user for optimizing the model performance over different regions.