Abstract:

Based on conventionally observational data, the NCEP reanalysis data and satellite cloud image, a rainstorm process caused by Northeast China cold vortex in the southwest of Heilongjiang province on June 18-19, 2009 was analyzed and simulated by a WRF numerical model. The effects of weather system and mesoscale characteristics were discussed. The results indicate that the heavy rain is caused by warm-wet shear in front of Northeast China cold vortex. Cold vortex moves slowly because of impeding effect of Okhotsk high, which leads to increase of precipitation. The strong convergence and updraft of strong southeast warm-wet airflow on the shear provide dynamic conditions for the heavy rain, while low-level jets supply abundant water vapor for the heavy rain. The increase of temperature and humidity in the low level makes atmospheric stratification unstable. Low strong convergence area and upper strong divergence area overlay, which consequently leads intense ascending movement. It provides conditions of deep convection development and promotes the formation and maintenance of mesoscale system when heavy rain occurs. Rainstorm is caused by development and movement of several mesoscale cloud clusters that is in the cloud belt of warm front. The mesoscale convergence line on the ground provides the advantageous conditions for the development and maintenance of mesoscale cloud clusters. The numerical simulation result suggests that rainstorm happens because two mesoscale shear lines develop and move successively in the same region. There is a mesoscale vertical circulation which is related to rainstorm on the mesoscale shear line.

Key words: Northeast cold vortex, Secondary circulation, Mesoscale shear line, Numerical modeling, Rainstorm