Analysis on Causes of a Rainstorm Process in Dalian

The weather situation,water vapor conditions and active conditions of a rainstorm weather on July 10,2006 in Dalian were analyzed by using conventional meteorological data,cloud image and MM5 model,it was found out that the rainstorm was a convection weather caused by the interactive action of upper through,shear cloud behind subtropical high,peripheral cloud system of north forwarding typhoon and surface through.The multiple meso-β scale convective cloud continuously emerging and enhancing from shear cloud was the direct mesoscale system of this rainstorm.The analysis results of MM5 model exposed that,during this rainstorm process,there was strong south-west low-level jet in the lower troposphere,plenty water vapor of typhoon and southwest flow transported water vapor and heat to the precipitation area;the structure of shear line was characterized by lower convergence center and upper divergence center,intensive ascending motion over the vertical motion field provided powder conditions for rainstorm;the thick water vapor column and heat layer over the precipitation area provided abundant water vapor and energy for the generation of this rainstorm.The intrusion of cold air in the precipitation area was the trigger mechanism;while the location of subtropical high and its intensity change also played an important role in this rainstorm.