国家重点基础研究发展计划 973计划 国家自然科学基金项目41475055 41775048 41475061 科技基础性工作专项2013FY112400国家重点基础研究发展计划（973计划）项目2015CB452804，国家自然科学基金项目41475055、41775048、41475061，科技基础性工作专项2013FY112400
1.State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 100081;2.Beijing Weather Modification Office, Beijing 100089;3.Guangdong Meteorological Observatory, Guangzhou 510080
Found by Foundation:National Basic Research Program of China (973 Program) Grant 2015CB452804;National Natural Science Foundation of China Grants 41475055 41775048 41475061;Science and Technology Basic Project Grant 2013FY112400Found by Foundation:National Basic Research Program of China (973 Program) (Grant 2015CB452804), National Natural Science Foundation of China (Grants 41475055, 41775048, 41475061), Science and Technology Basic Project (Grant 2013FY112400)
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.