Analyses And Numerical Simulation On Two Snow Storms Occurred In Changjiang-Huaihe River Basin

Based on NCEP and other observational datasets, the nonhydrostastic mesoscale model MM5 (V3.6) was used to simulate the two snowstorms occurred in Changjiang-Huaihe river basin during February, 2003 and November, 2003. The comparisons between results of numerical simulation and objective analysis have shown that MM5 has the ability to replicate large-scale and mesoscale circulation systems. The results of numerical simulation indicate that MM5 can successfully simulate the genesis, development and evolution on structure of snowstorm's mesoscale vortex. The analysis of low-level jet shows that the low-level Southwest jet has close relationship with snowstorm. It also can guide snowstorm accurately. The diagnoses of cross-section on vorticity field, divergence field and vertical velocity field show that the allocation and coupling between motion field and thermal dynamic field could create favorable condition for development of snowstorm shear line and formation and maintain of snowstorm. The spatial and temporal evolution of simulated velocity and cloud microphysics fields show that the coupling of vertical velocity and vapor distribution is a kinematics criterion for vapor condensation and freezing that result in snow. The coupling of cyclonic vorticity column and ascending motion as well as deep moist tongue is one of the important dynamical mechanisms for the formation of the snowstorm. The simulation of radar reflectivity factor indicates that the simulation of snowstorm's precipitation distribution and intensity were reasonable. The analysis of temperature shows that the characteristic of precipitation is directly related to temperature advection on 700hPa and 850hPa . Wet Q vector divergence is the main dynamical mechanism of heavy precipitation. It also analyse from some aspects such as pparent heat source,apparent moist sink helicity and potential vorticity In the end some sensitive experiments was carried on such as wind wind, humitidy field and topography field. It opens out the dynamic and thermodynamic condition of strong precipitation during Spring and Winter in Changjiang-huaihe river through the dynamic and thermodynamic analysis of the two weather process. It could grow on knowing of snowfall's occurring and development.