梅雨暴雨中高低空急流与西南涡的活动

利用MM5中尺度模式对1991年7月5日00时-6日12时的降水进行了数值模拟。通过对每3h一次模拟结果的诊断分析，发现高空急流的走向与西南涡的活动关系密切，当我国东部位于西北风急流时，西南低涡稳定少动；位于西风急流时，西南涡快速东移；位于西南风急流时，西南涡加强，移速减慢。暴雨活动与西南涡的东移一致。最初暴雨区稳定少动，之后暴雨区快速东移，后期暴雨区缓慢移动。湿位涡对西南涡的斜压性加大有重要的贡献。在西南涡斜压性未建立之前以及冷锋附近，雨区可位于低层西南风急流左侧的任何位置，当低涡的斜压性加大，出现暖空气的作用时，暴雨区均出现在西南风急流的左前方。

Upper Low Level Jets and Activities of Southwest Vortex in a Torrential Rain Process during the Period of Meiyu

In this paper, the mumerical simulation of precipitation during the period of 0000Z 5th to 1200Z 6th July 1991 is carried out by using the MM5 meso-scale model. Through the diagnostic analysis of simulated 3-hour interval results, it is found that the trend of upper level jet was close related to the motion of southwest vortex. When the northwest, west and southwest jet lay over the east of China, the southwest vortex was stationary, moved eastwards rapidly, and strengthened and moved slowly, respectively. Meanwhile, the motion of rain core was consistent with the eastward motion of the southeast vortex. At first, the rain belt was stationary, then it moved quickly eastwards, and at last, its movement became slow. Wet potential vorticity had a great contribution to the stronger baroclinicity of the southwest vortex. Before the baroclinicity of southwest vortex had not been built and in areas near the cold front, the rain belt might lie in anywhere of the left of southwest low level jet, but when the baroclinicity of low level vortex was strengthened and when the warm air came into being, the rain belts all occurred in the left front of southeast low level jet.