Mechanism Analysis of a Short-term Strong Precipitation in Midsummer of 2012 in Western Shandong Province

The paper analyzed the weather situation,physical quantity condition and the characteristics of satellite cloud images and radar echo on July 4 2012 in western Shandong Province by using conventional observation data,intensive observation of automatic weather station as well as satellite images and radar data. The results show that this short-term strong precipitation was caused by the lower cold air and the mesoscale weather system under the background of the propitious large-scale weather system. Abundant water vapor and the strong convergence ascending motion on the level of 925 hPa and 1 000 hPa were conducive to the occurrence of strong precipitation. The positive vorticity center was corresponding to the strong precipitation center,and the surface convergence line and cyclonic circulation touched off the short-term strong precipitation. The satellite cloud images and radar data revealed the occurrence and development of the mesoscale weather system. The position and the maintain time of the mesoscale convective cloud cluster were consistent with the mesoscale system,and the same as the short-term strong precipitation. Strong radar echo region with composite reflectivity factor more than 45 dBZ corresponded with the area of the short-term strong precipitation. Appearance and maintenance of the convergence flow field in radar radial velocity product were associated with the mesoscale cyclonic circulation,as well as the echo top height rising. While appearance and maintenance of the divergence flow field,and decline of the echo top were associated with weakening of the mesoscale system. The peak of the vertical accumulated liquid water contend appeared at the early stage of the short-term strong precipitation,and the peak value occurred before the stronger precipitation.