COMPARISON EXPERIMENTS ON CUMULUS PARAMETERIZATION SEHEMES OF THE MM5

Numerical simulation experiments on cumulus parameterization schemes, KUO, GRELL, KAIN-FRITSCH and BETTS-MILLER (KU, GR, KF and BM), of the MM5 are carried out using real-time data of the Shijiazhuang torrential rain event happened in Aug. 3-4 of 1996, under three kinds of model horizontal resolutions (60, 20 and 10 km). Comparisons among the experiments and against the observations indicate that the higher the model resolution is, the closer the simulations of main rain-belt distributions to the truth are, while the location of main rain-belt is not very sensitive to the cumulus parameterization schemes (CPSs). And spurious rainfall centers occurred when the model resolution increased to 10 km. In addition, the intensities of torrential rainfall increase with the decrease of the model grid size and change with the CPSs quite clear, but the torrential rainfall amount is underpredicted in all experiments. It was found that the contribution of the sub-grid scale precipitation to the total by KU scheme is higher than that by its three counterparts, and has an unreasonable trend of increasing with the model resolution, which is opposite from GR, KF and BM schemes. Although the characteristics of the horizontal circulation from four CPSs' simulation results are nearly the same, the certain differences of distributions of the cloud water, rain water and vertical motions among four CPSs' simulation results are obvious, which could affect the accuracy of the quantitative precipitation, the cloud amount, the surface air temperature and humidity forecasts. Therefore, choosing suitable CPSs for one's study is necessary.