Precipitation parameterization in a simulated Mei-Yu front

Observational and numerical studies have consistently shown the importance of latent heat release associated with frontal precipitation in the develop ment of a Mei-Yu front. However, a systematic evaluation of precipitation p arameterization in the simulation of a Mei-Yu front has been rare in the li terature. In order to enhance our understanding on precipitation parameteri zation of Mei-Yu fronts, this study conducts numerical experiments to evalu ate the performance of subgrid-scale cumulus schemes and resolvable-scale m icrophysics schemes to simulate the Mei-Yu frontal system on 4-5 June 1998 at grid resolutions of 45 km and 15 km, using the Penn State/NCAR mesoscale model MM5. Principal findings are summarized here. The horizontal extent and intensity of precipitation, the partitioning of p recipitation into grid-resolvable and subgrid-scale portions, the vertical thermodynamic profile in the precipitation region and the embedded mesoscal e structure are extremely sensitive to the choice of cumulus parameterizati on schemes. This is true for both the 45- and 15-km grids. The partitioning of precipitation into subgrid scale and resolvable scale i s sensitive to the particular cumulus parameterization that is used in the model, bat it is nearly the same on both the 45- and 15-km grids for a give n cumulus parameterization. The detailed ice-phase microphysical processes do not have a significant im pact on the rainfall pattern on either the 45- and 15-km grids. However, th e inclusion of cloud ice-snow-graupel microphysical processes increases the total surface precipitation amount by 30% compared to the amount with. onl y warm rain processes. Variations in the subgrid-scale cumulus parameterization have a much larger impact on the distribution and amount of Mei-Yu frontal precipitation than do variations in the resolvable-scale microphysics parameterization at mes oscale grid resolutions of 10-50 km.