Abstract:  Based on the conventionally meteorological observation data, satellite cloud images, Doppler weather radar echo data, the data from automatic weather stations and the NCEP/NCAR reanalyzed data (1°×1°), a short-time rainstorm process on July 30, 2011 in Liaoning province was analyzed. The results show that upper trough at 500 hPa and shear line at 850 hPa form the forward-titling trough which provides favorable instability conditions for generation of rainstorm. The mesoscale analysis suggests that the temporal and spatial variation of precipitation is significant. The intensive contour zone of TBB and the location of the overshooting cloud of convective systems are indicative to the falling area of rainfall. The intensity of radar echo generally reaches 65 dBz during the strong rainfall and there exists the inversion wind area, and a couple of positive and negative winds. The mesoscale and microscale strong convective characteristics are significant. The dense area of isotherm and the surface shear line (or the mesoscale low pressure) trigger together mesoscale rain cluster, and the intensity of rainfall strengthens sharply. The dynamic mechanism of shear line formation is diagnosed by a vorticity equation, and it suggests that when the positive vorticity variability increases, shear line moves to its large value area and generates the dynamic convergence lifting conditions. Divergence contributes greatly to vorticity variability, and strong convergence is one of the dynamic mechanisms of shear line formation in low level.

Key words: Forward tilting trough, Thermodynamic instability, Mesoscale characteristics, Dynamical mechanism