台风“云娜”(2004)近海加强的数值模拟研究

NUMERICAL SIMULATION OF TYPHOON RANANIM(2004) INTENSIFICATION

本文利用非静力平衡的中尺度模式MM5(V3)对2004年14号台风RANANIM("云娜")在登陆前近海加强及登陆初期的过程进行了54 h模拟,并加入人造台风优化初始场。结果表明:MM5能比较好地模拟出台风近海及登陆初期的移动路径及台风中心气压的变化。利用数值模拟结果,讨论了RANANIM(2004)台风在近海加强过程中的环流、动力和热力结构特征。发现在台风RANANIM近海加强的过程中对应有高空200 hPa净辐散场的存在,台风中心气压随净辐散值的增大而降低,反之亦然。净辐散值的减小对台风中心气压的快速升高有着预示的作用;垂直环流在强度和空间分布上发生了明显的变化。台风加强后,台风中心上方出现了明显的补偿性下沉气流;对流层低层存在明显的冷暖空气堆积,且当冷暖空气强度相当时有利于台风的增强;台风中心上方的正涡度柱逐渐发展为东西不对称分布,垂直方向上伸展高度保持不变或升高,而且在量值上也要更大。

Using the Penn State-NCAR non-hydrostatic mesoscale model（MM5）, the intensification stages before landfall and the initial stage after landfall of typhoon RANANIM are simulated. At the same time, the bogus typhoon data were used to optimize the initial field. Verified against observations, the track, minimum center pressure were well reproduced. By use of the high-resolution data from the model, the characteristics of typhoon during intensification stages are analyzed in circulation and dynamical and thermodynamic structures. Results are as followed： 200hPa average net divergent field existed during the intensification stages, the typhoon minimum center pressure decreased with the increasing of net divergence, vice versa; vertical circulation has changed greatly in spatial distribution and intensity. The apparent downdraft appear after typhoon intensification in the upper level of the center of typhoon; colder and warmer air accumulated in the lower troposphere and when their intensities are equivalent it is fit for intensification; the positive vorticity in the upper level of typhoon changed from symmetry to a symmetry, the vertical extension height maintained or increased and the extremum became larger.