Climatology Of Winter Extratropical Cyclones Over East Asia And Northwest Pacific And Their Surface Impacts On Yellow Sea And Bohai Sea

Extratropical cyclones(ETCs)are baroclinic low pressure vortices over mid and high latitudes of the two hemispheres,which are responsible for the weather variability and causing serious natural disasters.Therefore,the study of the climatic characteristics of ETCs is of great importance in terms of understanding weather variability and climate change.Firstly,by applying an automated Lagarangian ETC identification and tracking method to ERA-Interim reanalysis data(1979-2018),ETCs over East Asia and the Northwest Pacific are firstly identified and tracked.In this thesis,the wintertime ETCs over East Asia and the Northwest Pacific were clustered,and their climatic characteristics were statistically analyzed.The associations of three atmospheric teleconnection patterns(Western Pacific,WP;Pacific/North American,PNA;Arctic Oscillation,AO)with ETCs were investigated by using composite analysis.More specifically,the continental cyclones originating on East Asia inland and then entering the Yellow Sea and Bohai Sea(YBSs)were investigated.These ETCs were clustered into three groups and the differences of cyclone features in these three groups were compared.Finally,the surface impacts of ETCs on YBSs were also studied from the perspective of surface winds and surface air temperature as well as sea surface temperature.The main findings and conclusions:(1)The 850-h Pa relative vorticity field derived from the ERA-Interim reanalysis could be used for detecting and tracking cyclones,when the Lagarangian ETC identification and tracking method is applied.The probabilistic clustering algorithm plays well in classifying these ETC tracks,where the spatial consistency of trajectories belonging to different clusters could be effectively maintained.(2)The genesis positions of ETCs over East Asian and the Northwest Pacific are distributed at Mongolia,the east coast of China and the east of Japan.Then the ETCs usually move northeastward.There are negative correlations between the ETCs number and WP,and more cyclones usually occur in the negative phase of WP.In contrast,there is positive correlation between the ETCs number and PNA.(3)These ETCs entering and crossing Bohai Sea and Yellow Sea are classified into three groups,where their geographical positions of cyclogenesis and cyclone tracks could be identified and distinguished.The differences of cyclone features on three time points,before entering the YBSs,crossing the YBSs,and leaving the YBSs,are obvious.The surface impacts of ETCs on YBSs include strong surface winds and the change of surface air temperature and sea surface temperature(SST).Innovation points :(1)By applying the probabilistic clustering algorithm,the extratropical cyclones are classified according to the origin and track,the climate characteristics of cyclones are analyzed according to the clusters,which can better understand the differences between the climate characteristics of extratropical cyclones.(2)Focus on the extratropical cyclones in the Yellow Sea and Bohai Sea,and their impact on China’s coastal zone.