高空冷涡影响台风Meranti(1010)北翘路径的集合预报分析

路径突变是台风路径预报中的一个难题。2010年第10号台风Meranti（1010）在台湾岛南部海域西移过程中突然北折，而欧洲中期天气预报中心（ECMWF）集合预报对其北翘路径存在较大分歧。选取预报成功与不成功两组集合成员各8例，对比分析台风Meranti路径变化的主要原因。结果表明:（1）一个来自热带对流层上部槽的切断高空冷涡（UTCL）是该台风路径变化的一个重要影响系统。Meranti北翘路径跟它与UTCL的南北向耦合有关；（2）UTCL通过改变台风上层的环境气流影响台风引导气流。在UTCL移至台风北部过程中，台风的偏南风引导气流明显加强，有利于其路径北翘；（3）UTCL对台风Meranti北翘路径的影响还与其自身结构有关。水平环流宽且气旋性涡旋向下垂直伸展更深的UTCL对台风路径变化影响更明显；（4）位涡倾向方程的诊断分析表明，在TC与UTCL南北向耦合过程中，台风北部的正位涡水平平流项输送显著，有利于台风向北运动，且UTCL影响下产生的非对称风场在其中起主要作用。

An Ensemble Analysis on Abrupt Northward Turning of Typhoon Meranti (1010) under the Influence of an Upper-Tropospheric Cold Low

The sudden change of typhoon track is a challenging issue in typhoon forecast. Typhoon “Meranti” (2010) experienced an abrupt northward turning when it moved westward to the south of Taiwan Island. Ensemble forecast based on the European Medium Range Weather Forecasts (ECMWF) presented a large spread for the northward turning. The good group that consisted of eight members and predicted the abrupt northward turning is compared to the poor group that didn’t predict the unusual track to study the main influence factors on the northward turning of typhoon Meranti. Results show that: (1) An upper-tropospheric cold low (UTCL) cut off from the tropical upper-tropospheric trough (TUTT) was an important factor impacting the typhoon track change. The abrupt northward turning of typhoon Meranti was related to the coupling between Meranti and the nearby UTCL in the north-south direction. (2) The UTCL could change the upper-tropospheric environmental flow around the typhoon, and influence the typhoon steering flow. When the UTCL moved to the north of Meranti, the southerly component of the steering flow was enhanced, which was helpful for the northward movement of Meranti. (3) The northward turning of Meranti was also associated with the vertical structure of the UTCL. The UTCL with wide and deep cyclonic circulation in vertical direction was more favorable for the track change. (4) The diagnostic analysis based on the potential vorticity tendency equation shows that, under the coupling between Meranti and the UTCL in the north-south direction, horizontal advection of potential vorticity to the north of the typhoon was strengthened, which was helpful for the northward movement of Meranti. And the asymmetric advection of symmetric potential vorticity made a major contribution to the northward track under the influence of the UTCL.