应用位涡分析1214号台风“天秤”异常路径

Analysis of potential vorticity perspective on abnomal path of 1214 Typhoon“Tembin”

1214号台风"天秤"在移动过程中出现异常转向的极端个例,其路径呈近180°逆转向,以及强度的多次变化,使得"天秤"的路径预报十分困难。本文采用NCEP再分析资料,从位涡的观点结合天气学形势分析,以及应用兰金涡的假设对台风"天秤"异常转向路径进行诊断分析研究。结果表明:(1)藤原效应,高空槽的东移,副高位置稳定少动是导致"天秤"接近180°转向的主要原因。(2)"天秤"与1215号台风"布拉万"的逆时针互旋是造成"天秤"异常路径的关键因子,在藤原效应中,"天秤"受到主要影响。(3)"布拉万"向西北方向的移动,影响了副高的西伸。高空槽通过对下游大陆高压的影响,进一步间接影响了"天秤"的运动,这类异常路径的形成是大尺度环境场与藤原效应相互作用的结果。

The nearly 180 ° steering path and variable strength of 1214 Typhoon ＂Tembin＂ make its forecasting more difficult. Relied on the NCEP reanalysis data, invertibility principle of potential vorticity combined with synoptic situation analysis, as well as assumption of Rankine vortex, the abnomal track of ＂Tembin＂ is investigated through isentropic potential vorticity diagnostic analysis and potential vorticity inversion. Results show that Fujiwara effect, which means the eastward shift of the upper trough and the stagnation of the subtropical high, is the main reason for the abnormal turning. The process of ＂Bolaven＂ moving to the northwest direction influences the westward extension of subtropical high. ＂Tembin＂ would be affected more obviously by binary interaction compared to ＂Bolaven＂. According to the influence on the continental high pressure, the upper trough has further indirect impact on ＂Tembin＂ movement. Counterclockwise cross-spinning is the key factor for abnomal path of ＂Tembin＂. This type of abnormal path formation is the result of the interaction between large-scale environmental field and Fujiwara effect.