Numerical Simulation And Diagnostic Analysis Of The Southern Rainstorm Of Typhoon Imbudo

Using the typhoon and precipitation data from 1996 to 2005, the typhoon effected Guangxi were studied. The results show: the typhoon effected Guangxi main occurred in the later period of flood season. The ratio of the typhoon rainstorm more than 10 stations was 38.4% and its fields were asymmetric.Then used MM5 to simulate the process of influencing guangxi of 0307 Typhoon "Imbudo" on the basis of the NCEP AVN data. It showed that MM5 can simulated main rainstorm belt and its' distribution characteristic very well and the rainstorm fields were asymmetric. Then using the model output with high spatial and temporal resolution we study the characteristic and mechanism of the rainfall in more detail.The analysis of Circulation indicated that the strength of South jet in west of the subtropical high pressure benefited the rainstorm and the asymmetry of rainstorm due to the asymmetry of the wind field of typhoon. The lasting strong southwest lower-level jet provided large-scale atmospheric circulation for upkeep of strong vorticity in the south of typhoon. The asymmetry of vorticity field was the leading cause of the heavy rainfall in the south of typhoon. The analysis of physical variables indicated that the Moisture of the rainstorm came from mandla gulf and there were distinct moisture transportation channel in Indo-China Peninsula. The most fields of physical variables were closely related to heavy rainfall, between the higher and lower layers of rainstorm positive and negative helicity column benefited itself s develop and maintain of rainstorm. The strength of convective instability and the development of moist potential vorticity lead to the strength of moist potential vorticity at the low layers,which contributes to typhoon rainfall.The terrain sensitivity test indicated that the distribution of Guangxi typhoon rainstorm relate to it' special terrain closely. The mountains in Guangxi southeast and northwest could enhance the typhoon rainstorm distinctly. It was found that when the multiplied result of mountain grads and vertical cross wind velocity reached maximum, the terrain has most notable effectiveness on enhancing typhoon rainstorm and the effectiveness of terrain lower than 400 meters is not distinctly. Hainan island has little impact on rainfall of typhoon in this way.