Winnie(9711)台风变性加强过程中的降水变化研究

Study on Rainfall Variation Associated with Typhoon Winnie (9711) during its Extratropical Transition Process

热带气旋变性过程是其结构、强度及其风雨分布发生显著变化的过程,常导致预报失败。基于T106格点分析资料、日本气象厅TBB资料以及MM5V3数值模式结果,对9711号台风Winnie变性加强过程中的降水变化特征及其机理进行研究。结果表明,Winnie台风变性加强过程中降水分布非对称性明显,强降水带首先出现在台风环流北部,之后向南弯曲,其强降水中心绕台风中心从北部顺时针转向东北和东南部。这种降水变化一方面与Winnie与西风带高空槽相互作用过程中环境风垂直切变明显增大,且其指向顺时针旋转有关。此间台风垂直结构发生明显倾斜,变性前期涡旋环流随高度增加先向北倾斜,发展到最强时又趋于垂直,之后又向东南倾斜。强降水区出现在垂直切变的下风方、台风气柱倾斜方向一侧。另一方面还与台风环流内冷、暖平流活动紧密相关,强降水落区与低层暖平流输送位置关系密切。对流涡度矢量垂直分量反映了Winnie台风环流内中尺度锋区与风垂直切变的相互作用,800hPa上的大值区对其强降水落区有较好的指示意义。

The extratropical transition （ET） process of a tropical cyclone will lead to a variation in the rainfall rate and distribution, which has long been a challenge to weather forecasters. Based on Chinese Meteorological Administration T106 data, satellite observed temperature of black body （TBB） data issued by Japanese Meteorological Administration and the Pennsylvania State University / National Center for Atmospheric Research （PSU/NCAR） numerical model MM5 output, the change of rainfall related to typhoon Winnie （9711） during its ET process is analyzed. Results indicate that the rainfall distribution displays a remarkable asymmetric feature. The heavy rainfall centers occur mainly in the northern part of the typhoon at first, and then move to the northeast and southeastern part of the typhoon circulation, revolving around the typhoon center clockwise during the ET process. Study shows that the change of rainfall distribution is related to the strong vertical shear of horizontal winds in the surrounding environment. It is found that the vertical wind shear is enhanced under the interaction between the typhoon remnant and the upper level westerly trough during the ET process, which is favorable for the rainfall concentration on theleft side of downstream of the shear. The locations of heavy rain change clockwise along with the direction of the vertical wind shear. Meanwhile, the vertical structure of the typhoon vortex slants with height, inclining considerably to the north at its transformation stage, then tending to become perpendicular at its re-intensification stage, and inclining to the southeast afterward. We found that the heavy rainfall occurs in the slanting direction of the typhoon vortex. On the other hand, the rainfall locations were also related to the thermal advection activities in the typhoon circulation, which have a good relationship with warm air advection at the lower layer. Moreover, the vertical component of the convective vorticity vector can reflect the impact of the wind vertical shear and mesoscale frontal zone in the ET typhoon circulation synthetically. Its high value area at 800 hPa can indicate the heavy rainfall position within the typhoon circulation.