Numerical simulation of a torrential rain in the northeast of huaihe basin partⅠ:model verification and the characteristics analysis of mβcs

During the life cycle of Typhoon Prapiroon in August 2000, a torrential rain occurred in its peripheral areas, and the 24-h rainfall at the rain center reached 800 mm. The torrential rain is simulated in this paper by using a nonhydrostatic mesoscale model (ARPS(V5.2)), and by employing the triply single-way nested-grids. The centers of nested Domain1, Domain2, and Domain3 are at (27.5°N, 117.5°E), (31.5°N , 119.5°E), and ( 33.5°N, 119.5°E), their grid lengths 45 km, 15 km, and 5 km, and their total grid points 75×75, 140×140, and 180×180, respectively. With the ADAS 3-D data assimilation system, the NCEP/NCAR reanalysis data of 1°×1°, radar echoes and GMS-5 satellite images are assimilated into the ARPS to simulate the torrential rain event. Simple ice phase scheme, Kain and Fritsch cumulus parameterization scheme are used. There are 35 layers in the vertical direction, and the vertical grid distance is 625 m. The integration is performed for 48-h from 0800 BST 29th to 0800 BST 31st. The results are analyzed, and compared with radar echoes, GMS-5 satellite images and surface intensive observations. Results show that the meso-scale heavy rain area between the 500mb trough and the subtropical high in the left-front of Prapiroon is well simulated by ARPS, and the simulated precipitation area and rainfall center are rather consistent with the observations. The contrast analyses of radar echoes observed and simulated with hydrometeors in the model atmosphere reveals the evolution of MβCS, and four convective belts converge over the vicinity of Xiangshui, and the comparison of simulated and observed skew T-logP diagrams further exhibits the instability in the torrential rain process. The persistent vertical wind shear provides kinetic energy for development of mesoscale convective systems, therefore is beneficial to the slantwise development of convection cells, and to the occurrence of heavy rain at a fixed point. Considering the similarity of model results and observations, the results of simulation can be used as the base of further research on the torrential rain process.