地形对台风Megi(2010)过岛阶段路径偏折影响的数值研究

采用谱逼近方法减小大尺度环境场模拟偏差,通过地形敏感性试验,研究吕宋岛山脉地形高度对台风Megi(2010)过岛阶段路径偏折的影响。模拟试验表明,谱逼近700 hPa高度层以上天气尺度风场分量的数值试验不仅能够反映大尺度环流对台风路径的引导作用,同时保留了中低层环流对地形影响的响应,较为准确地反映了Megi靠近和登陆吕宋岛过程中的持续南压过程,以及离开吕宋岛后的突然北折过程。在此模拟基础上,通过对地形高度敏感性试验结果诊断和影响区域空气质点进行后向轨迹分析,表明在台风向山脉靠近过程中,台风外围和内核环流均受地形影响,迎风坡存在明显气流辐合,有利于台风流场与南北向山脉之间出现北风急流和轨迹汇聚带,从而产生狭管效应,造成台风移动路径南折;而台风过山后,不仅受到地形次生低压涡旋的吸引,其东侧同样出现以南风急流和轨迹汇聚为特征的狭管效应,有利于台风路径向北偏折。

Numerical study on the topographic influence of the track deflection of Typhoon Megi (2010) during the island-passing period

In this study,numerical simulation and diagnostic analysis using model output data are conducted,in order to investigate the mechanism of track deflection of Typhoon Megi(2010) after its landing on Luzon Island.Next,the spectral nudging technique is adopted to reduce the error of the simulated large-scale environmental field.Based on the simulation results of the spectral nudging tests,terrain sensitivity tests are then conducted by varying the terrain height of Luzon Island.The temporal evolution of circulation structure and variable field are diagnosed to investigate the impact mechanism of high terrain on the typhoon track deflection.Finally,the southward movement when the typhoon approaches and lands on the island is displayed.The simulation results indicate that the simulation typhoon track of SNV700,which uses the configuration of nudging synoptic-scale wind component above 700 hPa,can reproduce the southward movement when the typhoon passes by the island and suddenly turns north after leaving the island,by reflecting both the steering role of large-scale environmental flow and the response of lower-level flow to the terrain.Based on the simulation results of the spectral nudging tests,terrain sensitivity tests are then conducted by varying the terrain height of Luzon Island.When the terrain height is reduced to zero,the simulated typhoon track is in correlation with the steering flow.The impact of high terrain leads the typhoon to turn to south(north) when the typhoon approaches(leaves) the high terrain,and the deflection degree increases as the terrain height increases.The results of the terrain sensitivity tests are diagnosed,and backward trajectory analysis of the affected areas is conducted,so as to investigate the temporal evolution of circulation structure and variable field when the typhoon approaches and crosses the island.The results show that the convergence center occurs in both the windward and leeward slopes,thus contributing to the gale center in these areas.In addition,a positive vorticity area occurs in the leeward slope,thereby indicating that secondary depression is induced,which appeals to the typhoon.Meanwhile,the outer and inner circulations of the typhoon are affected by the high terrain.The channeling effect contributes to the gale centers and confluent trajectories between the high terrain and typhoon center.The north(south) low-level jet in the windward(leeward) slope induced by the channeling effect leads the typhoon toward the south(north).