2011年秋季河南省两个暴雨日特征对比分析

利用常规观测资料、加密观测资料及NCEP 1°×1°格点再分析资料,对2011年9月13-15日河南省连续两个暴雨日进行了对比分析,结果表明:这两次暴雨的落区均呈狭长带状,副热带高压与低槽的相互作用使冷暖气团在河南省上空交汇。第一个暴雨日为稳定性降水;第二个暴雨日对流性加强,有雷暴产生。第一个暴雨日中,锋面呈现出高低层基本一致的倾斜状态,暖湿气流沿着锋面倾斜上升;第二个暴雨日中,800-500 h Pa附近锋面陡立,产生了对流不稳定层结,强上升气流在750-500 h Pa附近接近于垂直发展,强度也显著增加。风场分析表明,第二个暴雨日,低层850 h Pa风速加强,而500、700 h Pa风速减弱,低层动力及热力作用的加强导致了不稳定因素增加。MPV1的演变表明,第一个暴雨日,锋区内部均为对流稳定;第二个暴雨日,MPV1正值带断裂,产生对流不稳定层结。MPV2的演变表明,第一个暴雨日,锋区存在着强斜压性及风垂直切变;第二个暴雨日,MPV2负值带断裂,斜压性加强,但风垂直切变有所减弱。

Comparative Analysis on the Characteristics of Two Rainstorm Days in Autumn 2011 over Henan Province

On the basis of the conventional observational data, intensive observational data, and NCEP 1°×1°reanalysis data, the two successive rainstorm days from 13 to 15 September, 2011 over Henan province were contrasted and analyzed. The results show that the rainstorm falling areas in two days are both narrow and long. The interaction of subtropical high and trough resulted in the mixing of warm and cold air over Henan province. The former belongs to stable precipitation while the convection of precipitation was enhanced and caused thunderstorm in the second rainstorm day. In the first rainstorm day, the front was slant from low to high level, slantwise warm and wet flow ascended along the front. In the second rainstorm day, the front was very stiff from about 800 to 500 hPa and some cold air moved above warm air which resulted in convectional unstable stratification. Strong updraft developed vertically and intensified at about 750 to 500 hPa. The analysis of jet stream or extreme wind speed zone show that in the second rainstorm day, wind speed increased at 850 hPa and decreased at 500 and 700 hPa which resulted in the steep front at corresponding levels. The increases of dynamic and thermal effects lead to enhancement of unstable effects. The analysis of MPV1 indicated that it was convective stable inside front zone in the first rainstorm day, however, the breakup of positive MPV1 zone caused the convective instable in the second day. The analysis of MPV2 indicated that powerful baroclinicity and vertical wind shear appeared in the first rainstorm day, but in the second rainstorm day, the negative MPV2 zone broke, baroclinicity was strengthened while vertical wind shear was weakened.