Abstract: During 20-22 July 1998("98.7"),an abrupt extraordinary heavy rainfall occurred in the eastern and southwestern parts of Hubei Province,especially in Wuhan periphery,which is seldom in the Changjiang River basin.Observational analyses indicate this event was in close relationship with the short wave trough at 500 hPa and a low vortex with shear line at 700 hPa as well as successive generating and developing of βMCS along the shear line.This event has successfully simulated for 36 hours using the fifth-generation Pennsylvania State University-NCAR Mesoscale Model Version 3(MM5.V3).This MM5.V3 includes full moist physics and two ways with quartet nest grid as well as FDDA of analysis nudging.The results pronouncedly improved previous simulation of the two-and-triple nest grid,especially,the nest subdomain D04 with 2 km horizontal resolution was able to simulate correct heavy rainfall area and raininess,further revealed the structures and evolution of the genesis and development on meso-β systems producing intense heavy rainfall.The main results include:(1)The genesis and development on a meso-β low vortex not only were in directly relationship with intense development of a meso-β low-level shear line along the Changjiang River in the east Hubei and the occurrence of a convergence center,but also in close relationship with the fozmation,development and maintenance of a thick southwest lowlevel jet stream;(2)The structural vertically features of the intense development on the meso-a shear line showed that the intense convergence and divergence layers were reiteration and coupling development with intense ascending motion,while the intense vorticity and potential vorticity as well as convergence layers were interadjoint,the moist potential temperature center in low levels and the saturated vapor belt in middle levels were in coexistence; (3) The structural vertically features of the genesis on the meso-β low vortex indicated that the divergence and ascending motion displayed double-branch column development,the vorticity and potential vorticity displayed one branch column development,the high moist energy column displayed double branches coupling development,the moisture channel displayed step slantwise ascending; (4)The structural vertically features of the development on the meso-β low vortex showed that the letterV typical columns of the divergence and ascending motion merged intercoupling development,the vorticity and potential vorticity were double branch column,the double branch high moist energy column intensely developed,the step slantwise ascending moisture channel changed into wider and deeper.Up to this stage the development of the low vortex reached the most intension,while this structure was possessed of the typicality.After this stage,the structural evolution of the low vortex showed the vertical circulation and ascending motion had been weakening,in the mean while,interadjoint the vorticity and potential vorticity double branch column as well as the double branch high moist energy column and the step slantwise ascending moisture channel was also weakened.The results are in directly relationship with the weakening meso-β low vortex.The simulative results also indicated that the development of a multiple nest technology with high temporal and spatial resolution and the application of FDDA method will be helpful to understand more the structure and evolution of the genesis and development on the meso-β severe convective systems,while it will further enhance predictive capability for heavy rainfall area and raininess.