西北地区退耕还林对区域气候的影响

利用NCEP再分析资料对2009年3月20日夜至21日凌晨豫北强对流天气过程进行了分析，结果表明：①导致这次强对流天气发生的湿位涡场分布特征为，对流层低层MPV1〉0，同时MPV2〈0；强对流发生时，对流高层表现为MPV1〉0，同时MPV2〈0，即高低层均为异常的湿对流稳定区。②强对流的发生发展与湿位涡的时空演变有着很好的对应关系，对流层高低层湿位涡“正负区垂直叠加”的配置是强对流天气发展的有利形势。这次强对流天气发生在低层湿位涡正压项等值线密集的零线附近以及大于零的区域和湿位涡斜压项的负值区，同时高层为湿位涡正压项等值线密集正值区域和湿位涡斜压项的负值区。③中低层急流和地面东路冷空气入侵高温高湿不稳定区是形成这次强对流天气的主要原因，中尺度对流云团是造成此次强对流天气的直接影响系统，且强对流发生前，近地面存在逆温层。

Analysis and Application of MPV in A Spring Severe Convective weather in The North of Henan Province

The severe convective weather processes were analyzed in the night of 20 to the morning of 21 March 2009 based on the NCEP data in northern Henan province. The results showed that： ① The characteristics of moist potential vorticity which led to the severe convective weather were MPV1〉 0 and MPV2 〈0 in the lower troposphere. The top troposphere showed MPVI〉 0 and MPV2 〈0 when there was the severe convection. That was the top and lower level were exceptional stability zone of moist convection. ②The development of severe convection corresponded with the temporal and spatial evolution of the moist potential vorticity. The positive and negative vertical stacking area ot the upper and lower MPV was conducive to the development of severe convective weather. ③ It resuhed in the severe convective weather that the low-level jet stream and east cold air of ground invaded the hot and humid unstable region. Mesoscale cloud cluster was the direct impact weather systems for the severe convective weather. There was the inversion layer near the ground before the occurrence of severe convection