Effects of turbulence-induced collision enhancement on heavy precipitation: The 21 September 2010 case over the Korean Peninsula

摘要

The effects of turbulence-induced collision enhancement (TICE) on a heavy precipitation event that occurred on 21 September 2010 over the middle Korean Peninsula are examined. For this purpose, an updated bin microphysics scheme incorporating TICE for drop-drop and drop-graupel collisions is implemented into the Weather Research and Forecasting (WRF) model. The numerical simulation shows some differences in the strong precipitation system compared to the observations but generally captures well the important features of observed synoptic conditions, surface precipitation, and radar reflectivity. While the change in domain-averaged surface precipitation amount due to TICE is small and similar to that due to small initial perturbations, the spatial distribution of surface precipitation amount is somewhat altered due to TICE. The surface precipitation amount is increased due to TICE in the area where the largest surface precipitation occurred, but the effects of different flow realizations also contribute to the changes. TICE accelerates the coalescence between small cloud droplets, which induces a decrease in condensation and an increase in excess water vapor transported upward. This causes an increase in relative humidity with respect to ice at high altitudes, hence increasing the depositional growth of ice particles. Therefore, the ice mass increases due to TICE, and this increase induces the increases in riming and melting of ice particles. A series of these microphysical changes due to TICE are regarded as partially contributing to the increase in surface precipitation amount in some areas, hence inducing alterations in the spatial distribution of surface precipitation amount.