热带气旋“莫拉克”在台湾岛登陆前后结构与路径演变机理分析

Mechanism and evolution analysis of the structure and track of the tropical cyclone Morakot before and after landing on Taiwan Island

采用全球预报场分析资料、卫星云图资料及实况观测台风强度、路径资料对2009年热带气旋"莫拉克"在台湾岛登陆前后其结构、路径的演变特征进行了动力学分析,以揭示其演变机理。分析结果表明:(1)热带气旋低层、切向风中心外侧的惯性稳定度低值区,有可能产生径向上加速内流的径向风,其对热带气旋结构的分布产生影响;(2)β效应项产生的高低层通风气流、以及高低层涡旋中心相对位置对热带气旋路径的预报具有重要意义;(3)登陆前后热带气旋尺度在经向上拉伸,在纬向上收缩,这种结构演变对移动速度产生影响;(4)低层辐合中心、正的涡度平流中心量级相当,是影响热带气旋强度与结构演变的重要因素;(5)通过EOF方法分解的500 h Pa位势高度距平场其第1,2模态很好地揭示了热带气旋环境场的演变。

GFS analytical data obtained by NCEP,satellite cloud image data and real-time observation data about the strength and path of tropical cyclone Morakot( 2009) were applied to make a dynamic analysis of the evolution characteristics of structure and track before and after its landing on Taiwan Island. The results show that,first,it is possible for the lower levels of tropical cyclone and low value area of inertial stability on the outer side of the center of tangential wind to form radial wind to accelerate the radial flow,which will exert an influence on the structure distribution of tropical cyclone. Second,the ventilation flow and vortex center at the high and low levels caused byβ effect will be of great significance in forecasting the path of tropical cyclone. Third,the structural evolution that the latitudinal of tropical cyclone stretched in the longitudinal direction and shrink in the zonal direction before and after landing will have effects on the speed of movement. Fourth,another important factor affecting the evolution of strength and structure of tropical cyclone is that the magnitude of the low-level convergence center and positive vorticity advection center should be equal. Last,the first and second modes of geopotential height anomaly field at500 h Pa decomposed by EOF could disclose well the evolution of environment field of tropical cyclone.