非纬向高空急流与远距离台风中尺度暴雨的研究

THE STUDY OF STORM RAINFALL CAUSED BY INTERACTION BETWEEN THE NON-ZONAL HIGH LEVEL JET STREAK AND THE FAR DISTANT TYPHOON

首先对非纬向高空急流与远距离台风暴雨的相关统计进行了分析,得出:暴雨发生时,200 hPa高空一般为西南风急流(90. %),暴雨区位于高空急流右后方。暴雨增幅时,200 hPa高空急流有一个增强转竖的趋势。用MM4模式对9711号台风8月19日00时～20日00时(GMT)进行了数值模拟和诊断分析。认为:远距离台风暴雨与非纬向高空急流、低层台风倒槽形成有关。高空急流右后方形成的高层辐散场主要与非纬向风有关。高层辐散场使低层产生变风场辐合,从而导致台风倒槽的形成与暴雨加强。在暴雨增幅过程中,用中尺度系统分析发现在高空急流右后方300 hPa以下存在一支中尺度环流,该环流对暴雨的维持与加强有密切联系,它的生成与高空急流的非纬向性增强有关。在高空急流右后侧的次级环流与降水产生的潜热反馈、高空非纬向风场(v场)的增强之间存在一种有利于远距离暴雨增幅的正反馈机制。

In this paper, correlation statistics and analysis between the storm rainfall far from typhoon and non-zonal high level jet streak(NHJ) were carried out. The results show that: The high level jet streak(HJ) in 200 hPa is constantly SW(90.2 percent) during the period of which storm rainfall occurs. Rainfall area lies in the right behind regions of HJ axes. While storm is being intensive, the HJ has a trend that non-zonal feature become stronger. In terms of MM4 model, numerical simulation and diagnosis were carried out for 9711 typhoon on 19th to 20th August, 1997. The far distant rainfall storm is tightly correlative to the NHJ and low level typhoon trough. The divergence field of HJ is related to v component. The upper level can caused the allobaric wind convergence at low level. This is the result of the form of low level typhoon trough and the strength of the storm. By scale analysis , there exists one branch of middle scale transverse inverse circulation in the right entrance regions behind the HJ below the 300 hPa level, which is very important to the keeping and strengthening of rainfall storm. This branch of inverse circulation is relative to the reinforcement of HJ’s non-zonal characteristics. From the field of middle scale divergence field and non-zonal wind field we can find that: The stronger symmetry caused by transverse circulation in the two sides of HJ, rainfall’s feedback and reinforcement of HJ’s non-zonal characteristics leaded to positive feedback mechanism that was favorable of storm rainfall’s strengthening.