Impact of Cloud Microphysical Processes on the Simulation of Typhoon Rananim near Shore. Part I: Cloud Structure and Precipitation Features

By using the Advanced Regional Eta-coordinate Model (AREM), the basic structure and cloud features of Typhoon Rananim are simulated and verified against observations. Five sets of experiments are designed to investigate the effects of the cloud microphysical processes on the model cloud structure and precipitation features. The importance of the ice-phase microphysics, the cooling effect related to microphysical charac- teristics change, and the influence of terminal velocity of graupel are examined. The results indicate that the cloud microphysical processes impact more on the cloud development and precipitation features of the typhoon than on its intensity and track. Big differences in the distribution pattern and content of hydro- meteors, and types and amount of rainfall occur in the five experiments, resulting in different heating and cooling effects. The largest difference of 24-h rain rate reaches 52.5 mm h-1. The results are summarized as follows: 1) when the cooling effect due to the evaporation of rain water is excluded, updrafts in the typhoon's inner core are the strongest with the maximum vertical velocity of -19 Pa s-1 and rain water and graupel grow most dominantly with their mixing ratios increased by 1.8 and 2.5 g kg-1, respectively, compared with the control experiment; 2) the melting of snow and graupel affects the growth of rain water mainly in the spiral rainbands, but much less significantly in the eyewall area; 3) the warm cloud microphysical process produces the smallest rainfall area and the largest percentage of convective precipitation (63.19%), while the largest rainfall area and the smallest percentage of convective precipitation (48.85%) are generated when the terminal velocity of graupel is weakened by half.