THE SIMULATION STUAY OF THE EFFECTS OF UPPER STREAM SURFACE THERMAL FLUXES ON CHANG JIANG HUAIHE RIVER BASIN CYCLONE ACCOMPANIED WITH HEAVY RAIN

By conducting some numerical simulations foracy clone case in Changjiang Huaihe River basin,the combination effects of surface themal fluxes and large-scale flow patterns on cyclonic precipitation systemare investigated.The surface thermal fluxes distribution in the stage preceding development of the cyclone shows that there are two large areas of strong positive surface heatand moisture fluxes,one north area to the northeast of the cyclone,another south area underneath the upper stream low-level jet. Comparing the roles of surface thermal fluxes in the two areas by sensitivity simulations with holding fluxes in the two areas,the surface thermal fluxes in south area,especially the strong moisture fluxes occurring before development of the cyclone,make more substantial contributions to the later intensification of the cyclonic precipitation system.It causes cyclone deepening 4 hPa more and about 70 percent increment of the central intensity of 24 hour accumulated precipitation.The evaporated moisture from surface underneath the low-level jet in the early stage is transferred down stream into the middle and lower reaches of Changjiang river with southwest flow,and the accumulation of moisture there lead to moistenning oflower lay er,especially in the top of boundary layer,which causes slightly stabilization oflow levelairand strong destabilization above boundary layer.This characteristics of stability is favorable for the accumulationo finstability energy and the intensification oflow-level jet near boundary layer top by reducing the vertical mixing of momentum,which also intensify the transfer of moisture.The downstreamaccumulation of moisture near bo undary layer top also causes front ogenesis,and enhances stratiform cloud and stratiform precipitation,whose releasing of latentheatis advantageous to the deepening of cyclone and the enhancing oflower level convergence intensifing the front secondary vertical circulation by the rapid release of the instability energy.By which the peak of heavy rainfall emerges.