台风“莫拉克”登陆前后的动力诊断分析

Analysis on Dynamic Diagnostic before and after Typhoon 'Morakot' Landing

利用NCEP 0.5°×0.5°每日4次的全球预报场分析资料GFS(Global Forecast System)、日本MTSAT静止红外卫星云图,对2009年第8号台风"莫拉克"在台湾登陆前后的演变特征进行了动力学诊断分析。结果表明:(1)由于近台风中心附近对流层中低层存在切向风大值区中心,使得水平位涡通量散度项在其内侧分布密集。(2)近台风中心低层的负水平位涡通量散度项指向正水平位涡通量散度项,可以很好地示踪台风在海上的移动。(3)p坐标系下的负垂直位涡通量散度密集区可作为分析台风移动的一个重要参考指标。通过涡度方程讨论了决定台风对流层中低层气旋性涡度变化的主要因子,指出南海、华南沿海地区夏季西南气流与台风的耦合对台风结构、路径产生了重要的影响。

Using the GFS（Global Forecast System） analytical data with 0.5°×0.5° grid intervals,the NCEP reanalysis data with four times a day and the satellite cloud image data,the evolution characteristic before and after the typhoon ＇Morakot＇ landing with No.8 are dynamically analyzed.Based on the diagnostic analysis of tendency equation of disturbed potential vorticity,the result shows that： Firstly,there exists centers of tangential wind near typhoon center at mid-and low-levels which lead to the intensive area of the horizontal flux divergence of potential vorticity located on the inner side of the center of tangential wind.Secondly,the negative and positive horizontal flux divergences of potential vorticity at low levels can be employed as a pointer for forecast the typhoon moving on the sea.Thirdly,the intensive areas of negative vertical flux divergence of potential vorticity offer reference for forecast of typhoon moving under the p coordinate.Finally,by using the vorticity equation,the principal determinants of the variation of the cyclone vorticity at mid-and low-levels are discussed.Meanwhile,the important coupling effect of typhoon and southwest low-level jet in coastal region of the South China Sea and Southern China on the structure and routine of this typhoon are also investigated.