To further explore tropical cyclones'(TCs) law and climate characteristics of occurrence, development and disappearance, this study applies Finite-Mixed-Model(FMM) which is based on clustering algorithms to cluster landfall tracks of TCs over China during summer and autumn(from June to November).The data of typhoon best-tracks and circulation fields are from the Shanghai Typhoon Institute(STI) of China Meteorological Administration(CMA) and 6-hourly reanalysis data of wind and other fields from NCEP/NCAR for the period 1951—2012 during summer and autumn.The three clusters are analyzed for comparison in terms of TC's active season, frequency and circulation.
The TC tracks landing China are divided into three categories by using FMM algorithm, which corresponds with the traditional classification result.Cluster-1 approximates the recurve-landing type, Cluster-2 approximates to the westward-landing type, and Cluster-3 approximates to the northwest-landing type.The findings are summarized as follows.In summer, Cluster-1 and Cluster-2 appear more frequently than Cluster-3, however, Cluster-3 has the highest frequency of occurrence in autumn.The generate location of Cluster-1 is the most northward, and the intensity is relatively strong.The track of Cluster-1's development shows northward trend, affecting the most extensive region, such as the Yangtze River Delta, the Pearl River Delta, Beijing, Tianjin and other economically developed areas, and even affect the Korean Peninsula and the Japanese Islands.The generate location of Cluster-2 is the most westward, its lifetime is the shortest and its intensity is the weakest, but it owns the highest frequency of occurrence.This type mainly affects China's Guangdong, Guangxi and Fujian.The generate location of Cluster-3 is the most southward, and its lifetime is the most enduring, but more inactive than Cluster-1 and Cluster-2.With respect to the track, this type slightly move to the northwest direction.Cluster-3 mainly affects China's Fujian, Zhejiang.
Through the analysis of the circulation situation, results are shown as follows.The west-extending ridge point of the subtropical ridge line's location of Cluster-1 is the most northward, and the southeast airflow turns to the southwest airflow around the cyclone, which leads to the minimum steering flow velocity.When generating, Cluster-1 has the lowest convergence degree, zonal wind vertical shear and water vapor transportation.The water vapor supply during the decaying process is also the weakest among the three classes, but still has a complete cyclonic structure.The west-extending ridge point of the subtropical ridge line's location of Cluster-2 locates the most westward, with the southeastward easterly airflow dominated by the cyclone.When disappearing, the convergence over the lower level is the weakest.The location of Cluster-3's west-extending ridge point is the most eastward and southward, and the southeast airflow turns to the southwest airflow around the cyclone, which leads to the maximum steering flow velocity.This cluster owns the strongest vertical zonal wind shear when occurring.Both in occurring and decaying stage, water vapor supply of Cluster-3 is the strongest among the three clusters.
The above work and conclusions not only enrich the research of TC tracks, but also provide reference for climate diagnosis and new ideas for scientific research in the field of data mining and meteorology.