江西汛期一次大暴雨过程湿位涡演变特征

摘要

利用自动气象站逐小时雨量资料和NCEP 1°×1°逐6 h再分析资料,应用湿位涡理论,对2011年6月江西汛期一次大暴雨过程的湿位涡的演变特征进行分析,其中主要分析了正压项(MPV1)和斜压项(MPV2)正负值范围以及其值的大小变化与暴雨强度、落区的关系。结果表明,此次大暴雨过程前期,以对流层低层的对流不稳定能量的释放为主。对流层低层MPV1<0,中高层MPV1>0,并且中高层有正值MPV1向低层输送,这样的高低空配置有利于低层对流不稳定能量的释放。低层MPV1等值线密集带零值线附近对应强降水中心区。此次大暴雨过程中后期,对流层中高层负值MPV2的绝对值和正值MPV1同时增大,其大值区南压,对流层中高层湿斜压性明显增强,使垂直涡度明显增大,同时伴随着对流层低层对流不稳定能量的释放,降水强度明显加强。从整个暴雨过程来看,暴雨落区的移动方向与对流层中高层MPV1正值区和MPV2负值区的移动方向一致,中高层湿斜压性的增强对暴雨增幅起了关键作用。%　　Based on automatic observation station data and NCEP 1°×1° reanalysis data, the theory of moist potential vorticity was applied to analyze the evolution characteristics of the moist potential vorticity during a heavy rain process in Jiangxi flood season. The analysis was emphasized on the relationships between the scope and size of horizontal components (MPV2) and vertical components (MPV1) and the intensity and falling area of the heavy rain. The results showed that in the early stage of the heavy rain process, the precipitation was mainly the result of release of convective instability energy in the lower troposphere. MPV1 in the lower troposphere was negative and positive in the middle and upper troposphere, and positive MPV1 transmitted downward. This situation was advantageous to the release of convective instability energy in the lower troposphere, and zero contour of MPV1 was corresponded with the rainfall center. The absolute value of negative MPV2 and positive MPV1 of middle and upper troposphere increased and moved to the south in the middle and late stage of the heavy rain process. At the same time, the middle and upper troposphere moist baroclinity significantly enhanced, which leaded to the development of slantwise vorticity and the significant increase of vertical vorticity, the lower troposphere convective instability energy released, and the precipitation intensity increased apparently. During the whole rainstorm process, the moving direction of the rainstorm zone corresponded with the moving direction of the middle and upper troposphere positive MPV1 zone and negative MPV2 zone. The enhancement of the middle and upper troposphere moist baroclinity had played a key role on the enhancement of rainstorm.