The Numerical Simulation And Diagnostic Analysis Of A Storm Rainfall Caused By Typhoon Fengshen (0806)

By using NCEP1°×1°reanalysis data, the article firstly analyses the active process of typhoon Fengshen (0806). By analyzing the typhoon occurrence of the development process through the weather situation and the physical changes, the article reveals the reason for the change of the path and intensity of the typhoon. The result shows that, subtropical high is the direct impact on the system of the moving path of typhoon. And the southwest monsoon is closely related with the typhoon intensity change.By using data of conventional observation, meteorological satellite and NCEP reanalysis data, we carried out a diagnostic study to the intensity andfalling area of Tropical Cyclone Fengshen. Results showed that (1) typhoon rainfall mainly happened in48hours after the landing of typhoon,the distribution of water flux divergence, the vertical velocity and absolute vorticity are best related with the heavy rainfall area;(2) Cold air intrusion into west part of the typhoon trough resulted in the release of unstable energy which reinforced the precipitation;(3) According to moist enthalpy and moist enthalpy field we can make a forecast about energy accumulation and future strong rainfall12hours in advance as high moist enthalpy is accumulation area of unstable energy and advection from typhoon pressure energy trough to moist enthalpy accumulation can reflect the falling area of rainfall after24hours rather correctly.On the basis of NCEP reanalysis data, the article simulates the typhoon process by using WRF mesoscale numerical model. And on the basis of the ideal simulation, we explore the characteristics and mechanism of the development of the typhoon rainstorm by using the high spatial and temporal resolution data of the numerical simulation. The asymmetric structure of the typhoon flow field directly impacts on the asymmetry of the rain distribution. There is a good correspondence between the lower-level OLR which is less than180w-m-2and the occurrence of the heavy rainfall. The area of the lower-level OLR which is less than120w-m-2can trigger the mesoscale weathe systems which contain strong thunderstorms, heavy rainfall and so on. And the lower-level OLR can make early warning of heavy rainfall and provide a reliable basis for tracking the strong rainfall.The vertical helicity diagnosis showed that there is a good correspondence between the vertical helicity and the distribution of precipitation. The positive large value corresponds to the heavy rainfall center. When the coincided center of vertical helicity extends to lower levels by the senior, the area of the heavy rainfall expands to the region accordingly. The larger the coincided center of vertical helicity, the greater the intensity of rainfall is.The moist potential vorticity diagnosis showed that when the heavy precipitation occurs the lower atmosphere is both in the symmetric instability, also in the convective instability. The wet potential vorticity evolution has a good indication of the evolution of the precipitation.