18th Conference on Weather and Forecasting, 14th Conference on Numerical Weather Prediction, and Ninth Conference on Mesoscale Processes

Monday, 30 July 2001
Impacts of parameterized convection on the numerical simulation of heavy rain over East Asia
Young-Youn Park, Yonsei University, Seoul, Korea; and T. Y. Lee
An investigation has been made to understand the impacts of parameterized convection on the numerical simulation of heavy rain over East Asia. This study considers two heavy rain cases during east Asian summer monsoon: 1) Case 1 - heavy rain produced by an eastward propagating disturbance which is initiated by a mesoscale convective system in eastern China, 2) Case 2 - heavy rain produced by an intense quasi-steady squall line. The two cases show significant differences in the process of heavy rain development. PSU/NCAR mesoscale model (MM5) is used for this study. Simulations are carried out on triply nested computational grids with the finest grid size of 2 or 5km depending on experiment. Parameterized convection is considered only for coarse grids while explicit microphysics is used for all grids. Convection schemes of Kuo, Grell, and Kain and Fritsch (KF) are considered for this study.

Parameterized convection in coarse grid significantly affects the explicit convection and rainfall in fine grid. Rainfall amount and peak location varies significantly with convection scheme. Rainfall amount in fine grid tends to be relatively small with KF scheme in coarse grid while comparable amount is obtained with Kuo and Grell schemes. For both coarse and fine grids, closer agreements between simulated and observed rainfall are obtained with Grell and Kuo schemes. Analysis of coarse grid fields has revealed significant variations in the impacts of parameterized convection on temperature and moisture fields of environment. It also indicates that the convectively available potential energy of air at the inflow boundary can be significantly larger with Kuo scheme than that with Grell or KF scheme. Such variation of impact is discussed relating the response of parameterized convection to the nature and atmospheric condition of convection. Further analysis of the simulated results will be presented focusing on the following aspects: 1) how parameterized convection in coarse grid affects the explicit convection in fine grid domain, and 2) how the performance of convection scheme is related to the nature of convection in the present heavy rain cases.

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