EXPLICIT AND PARAMETERIZED REALIZATIONS OF WARM-SEASON PRECIPITATION SEQUENCES OVER NORTH AMERICA

摘要

Radar-based observational analyses have documented coherent rain patterns of the order 1000 km in zonal span and 1-day duration over the continental United States. Such coherent patterns often result from sequences of organized convection and occur with high frequency in midsummer. Because of the “weakly forced” conditions and the deficiencies in existing convective parameterization schemes (CPSs), modern numerical weather prediction models have considerable difficulty in realizing the coherent sequences of warmseason precipitation. It is generally believed that the path to improved prediction requires either explicit representation of convection or an entirely new type of convective parameterization. This paper presents some results of our fine-grid explicit simulations of warm season convection and comparisons with coarse-grid simulations applying traditional CPSs. The major objective is to show both the promises and problems of the explicit simulations at grid spacings that are currently affordable and the relative performance of the explicit and parameterized modeling approaches.