局地海表温度异常影响热带气旋路径的模拟研究

A numerical study on the influence of abnormal local sea surface temperature on the track of tropical cyclone

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。

Taking Tropical Cyclone （TC） Megi （2010） for example, a set of sensitivity tests by using the Weather Research and Forecasting（WRF） model as well as different Sea Surface Temperature （SST） on Megi＇s track were carried out. SST from FNL reanalysis data of NCEP were used in CTRL experiment. EXP1 and EXP2 are performed with increasing and decreasing SST on the track before TC hiring Philip- pines. Results show that TC track simulated by CTRL is close to the observation, while tracks in EXP1 and EXP2 turn northward earlier and later than those in CTRL. TC track in EXP 1 shifts eastward, while in EXP2 it shifts westward. The reason why abnormal SST would result in different tracks is further ana- lyzed, which found that when TC passed over warm SST to the east of Luzon Island, its strength en- hanced, which generate an abnormal positive vorticity advection. Condensations of water vapor into rain with latent heat releasing are increased above 500 hPa. Thus, there is an abnormal positive temperature over the Sensitivity Region（SR） of the Western Pacific Subtropical High （WPSH）. Meanwhile, the mixing of hydrometeors and precipitation evaporation processes intensified below 500 hPa. Thus, tempera- ture over the SR of the WPSH is abnormally negative. Positive vorticity advection, the abnormal warming above and cooling below 500 hPa causes a decreasing in geopotential height at 500 hPa and a weakening of the WPSH. Thus, the range of the WPSH extension westward decreased. As a result, TC turns north- ward earlier and the track shifts eastward. On the contrary, when TC passed over cold SST to the east of Luzon Island, the range of the WPSH extension westward increased. Finally, TC turns northward later and shifts westward.