Sensitive experiments for effect of terrain on a torrential rain event in the midwestern Jiangxi

A spring torrential rain event in Ping Xiang area during May 2005 was firstly analyzed by using conventional observation data，intensiveobservation data and NCEP reanalysis data. The analyses showed that heavy rain only occurred in the south. Considering thesouth-central terrain in Ping Xiang，the evolution of the torrential rain event was reproduced by meso-scale atmospheric model，and threekinds of sensitivity tests were performed to investigate the impacts of different terrains on rainfall by raising，decreasing and removing the terrainelevation. The results indicated that the convergence of wind field caused by blocking affects of terrain was one of the important reasonsfor heavy rain in south. The difference in terrain would alter the location and intensity of torrential rain by influencing the convergence of windfield nearby shear line and the position and magnitude of water vapor supply. The higher terrain gave rise to the accumulation of air flowahead of the mountain, which caused measurable horizontal pressure gradient force. The convergences between local flow and backgroundflow owing to the pressure gradient force were in favor of precipitation in front of the mountain.