Abstract:By using MM5 nonhydrostatic mode,a numerical simulation was made successfully to a northeastern vortex and shear caused rainstorm occurring from August 8th to 9th in 1998.The numerical simulation revealed follow results:the strong divergence formed in upper air lead to the strong precipitation center in the northwestern part of the low vortex,the shear formed by convergence of the southerly jets with the easterly ones also contributed a lot to the precipitation,ascending motion with the shear was apparently lower than one with the low vortex.Meanwhile,the contrast test shows that the southerly jets play the most important role in transporting water vapor to the precipitation area.The weakening or strengthening of water vapor within the southerly jet zone had a direct impact on the precipitation,especially to the shear caused precipitation.The strenthening of westerly cold air made the baroclinic function become stronger,further lead to the enhancement of both the low vortex and the precipitation.While the southerly air current was detained by the easterly cold air,which resulted in the ascending motion and influenced on the shear intensity and its resultant precipitation.The blocking high made an obstruction to its upsteam low-pressure systems and influenced both their position and intensity,thus had further influence on the precipitation.