Impact of Initial Storm Intensity and Size on the Simulation of Tropical Cyclone Track and Western Pacific Subtropical High Extent

Typhoon Megi, the 13 th typhoon of the 2010 typhoon season, was selected for case study by utilizing the Weather Research and Forecasting(WRF) model. Twelve sensitivity experiments with various initial tropical cyclone(TC) intensities and sizes were conducted to investigate their impacts on the simulation of typhoon track. Interaction between TC and the western Pacific subtropical high(WPSH) was also analyzed to explore the mechanism for the impact on TC track of the initial TC intensity and size. Numerical results indicate that the simulated TC size and TC track are sensitive to initial TC intensity and size. Stronger initial TC intensity and larger initial TC size often lead to larger simulated TC size and make TC turn northward earlier. Further analysis suggests that, with the increase of initial TC intensity and size, more air mass enters into the TC region, which subsequently reduces the extent of WPSH.As a result, the steering flow changes significantly and eventually causes the TC to turn northward earlier. The present study confirms that the initial TC intensity and size have certain influences on the TC track simulation, which demonstrates the importance of accurate initial condition for successful simulation of the TC intensity and TC track.Moreover, it also deepens our understanding of the interaction between TC and WPSH, provides helpful clues for the TC track change study, and discusses the future directions for improvement of TC track forecast.

局地海表温度异常影响热带气旋路径的模拟研究

本文以热带气旋"鲇鱼"(2010)为例,利用WRF模式和"鲇鱼"移动路径上不同的局地海表温度(SST)强迫进行了敏感性数值模拟。控制试验(CTRL)采用NCEP的SST强迫,敏感性试验分别在"鲇鱼"登陆菲律宾前的路径上增加(EXP1)和减小(EXP2)SST。结果表明:CTRL试验模拟的热带气旋路径与实况非常一致,EXP1试验模拟的热带气旋路径提前转向,移动路径偏东,EXP2试验模拟的热带气旋路径转向滞后,且移动路径偏西。对SST异常导致热带气旋路径出现差异的原因分析发现,热带气旋在吕宋岛东侧经过异常暖SST海面时,热带气旋强度增强,产生异常的正涡度平流,且500 h Pa以上凝结潜热释放增强副热带高压敏感区出现温度场的正异常,500h Pa以下水凝物的混合和蒸发作用增强造成副热带高压敏感区温度场的负异常,加之正的异常涡度平流和异常的上暖下冷温度场配置使得500 h Pa位势高度降低,副热带高压强度减弱,副热带高压西伸范围减小,导致热带气旋提前向北转向,移动路径偏东。反之,当热带气旋在吕宋岛东侧经过异常冷SST海面时,副热带高压西伸范围扩大,导致热带气旋向北转向滞后,路径偏西。