Abstract:

Base on the 0.5°×0.5° NCEP- GFS reanalysis data, seven warm-dry heavy rain events from 2008 to 2011 in Hubei province were analyzed. The results indicate that positive vorticity advection doesn’t occur in large areas during a warm-dry heavy rain process, but moves with wind as a positive vorticity advection core, which leads to rapid variation of vorticity advection in different tropospheric layers over the heavy rain areas. This is easy to make the upward motion strengthened suddenly. Warm advection expandes from mid-upper troposphere to the whole troposphere; strong warm advection center appears in boundary layer where the heavy rains just occur; thermal forcing action leads to strong convergence in lower troposphere; locations of upper-lower strong warm advection center of 950 hPa and heavy rain area are similar; the above four conditions are indicative to prediction of warm-dry heavy rain. Invasion of dry air in the middle troposphere and warm-moist air in the lower troposphere is a main impacting factor for increase of convective instability in the heavy rain areas, and both are related to the westward development of subtropical high.

Key words: Warm-dry heavy rain, Positive vorticity advection core, Warm advection