Research Of Tracks Clustering And The Variation Of Cold Wave Based On FMM Algorithm

Cold wave is one of the most severe weather in the winter half year in China.The important research of its variation has been a key topic for meteorologists and meteorological department for a long time,but the lack of further research on objective and detailed classification of cold wave tracks,characteristics of their activities and influence mechanism.Based on the reanalysis dataset from NCEP/NCAR and dataset of daily surface climate data in China over 129 stations in the period of 1965-2015,the study applies finite-mixed-model(FMM)algorithm to cluster cold wave tracks.The variation trends and circulation characteristics of the four clusters of cold wave tracks are analyzed.Besides,this paper has analysed the different phases of Eurasian Teleconnection(EU)and the relationship between the change of cold wave frequency and tracks in China.It's not only offers new ideas for the study of different cold wave tracks in China,but also provides a theoretical basis for meteorological disaster prevention and mitigation.The main conclusions are summarized as follows:(1)The dataset of cold wave tracks in China has been formed in the last 50 years.There were four main tracks in the results of the FMM algorithm was adopted to cluster tracks of the dataset:Cluster-1 west veering,Cluster-2 north,Cluster-3 northwest,Cluster-4 west.The accuracy and scientificity of the FMM algorithm are verified through the analysis of the characteristics of cold wave tracks and a case of cold wave.(2)Their character of frequency,cold high pressure and circulation field are different.Cluster-1 appears most frequently and has obvious decreased tendency;Cluster-2 frequency is the least;the intensity of Cluster-3 is extremely strong;Cluster-4 occurred mainly in spring and frequency is gradual.During the cold outburst,temperature-pressure field configuration,transition of wind field,distribution of high-level advection of vortices and temperature and surface cold high pressure closely related with cold wave tracks.The low trough,Negative vortices area and cold advection area of Cluster-2 is significantly distribution of be east skewed,Cluster-3 is the exact opposite.(3)The change of EU phase is closely related to the frequency and track selection of cold wave in China,and the different phase of the EU can cause the atmospheric circulation anomaly in the Eurasian continent in winter,thus in turm the change of cold wave.The numbers of total cold waves had increased relatively,meridional circulation tended to be enhanced and the dry cold air moved southward,this typical circulation pattern tended to own more proportion of Cluster-2 north tracks in a positive EU winter.Contrarily,the situations in the negative EU phase,zonal circulation had increased relatively with the advent of moist cold air,there were more frequency relatively of total northwest tracks for Cluster-3.