Diagnostic analysis of a rainstorm event triggered by low-vortex shear in central Hunan

Diagnostic analysis was performed on a regional rainstorm triggered by low-vortex shear on 10 June 2011 in central Hunan with conventional observations, NCEP 6-hourly reanalysis data with resolution 1°×1°, hourly TBB data from FY-2E geostationary satellite IR imagesinversion and Changsha Doppler radar products. The results indicate that the rainstorm occurred against the circulation background of trough in the high level matching with low vortex in the mid- and low-level. The center of the rainstorm had vertical structure with positive vorticity (convergence) in the low-level and negative vorticity (divergence) in the high level. The severe precipitation during the event was not synchronized with the TBB minimum value, but lagged behind the TBB minimum value for 1-3 h, so the distribution of severe precipitation located significantly in the high TBB gradient area on the back of the cloud clusters. Echo of the rainstorm was a typical mixed precipitation echoes. The area where head wind zone passed is corresponding with the distribution of severe precipitation, within half an hour after the occurrence of head wind zone, the precipitation was severe. Precipitation significantly decreased after the disappearance of the head wind zone,while weak cold air in the middle level increased the convective instability of rainstorm areas.