Sensitivity of simulated summertime precipitation over the western United States to different physics parameterizations

Abstract

The parameterizations tested are a modification of the standard MM4 Kuo scheme, which imposes storage and slow release of condensation heat, an explicit moisture scheme, a version of the Arakawa-Schubert scheme, and a relatively sophisticated hydrology package. The standard MM4 strongly overestimates precipitation over mountainous terrain and, in particular, it produces an excessively large number of gridpoint precipitation events in excess of several centimeters ("numerical point storms' or NPS's). these are due to intense vertical motions maintained by large and localized condensation heat release. Both the explicit moisture scheme and the modified Kuo scheme reduce precipitation and number of NPS occurrences. Compared to the Kuo shcme, the Arakawa-Schubert scheme produces less convective precipitation, but still overestimates total precipitation and number of NPS occurrences due to interactions with the resolvable-scale precipitation proceses. -from Author