Climatic Effects Of Tropical Cyclone In Western North Pacific

Western North Pacific(WNP)tropical cyclone(TC)is an important weather system that affect China,and the study on its climate effect is the hot issue now.Using the best track data set provided by JTWC and NCEP-CFSR reanalysis data,the climate state and interannual effects of the WNP TC were analyzed for the period of 1979-2016 August to October.The research mainly focus on the change of temperature,geopotential height,850hPa relative vorticity,200hPa westerly jet between TC time and the absence of TC time.The relationship between the variation of East Asian south-west wind and monsoon trough and TC is also analysed.Comparing the difference of environmental variables between TC time and no-TC time.It is found that there is a significant positive relative vorticity anomaly in the TC distribution range in 850hPa,which indicates that the TC can be separated in this way.And the TC increases the relative vorticity of the region in the corresponding spatial distribution.With the increase of height,the positive anomaly of temperature is gradually obvious in the main area of TC distribution,and the negative anomaly of the potential height is gradually reduced,and the positive anomaly in the north of TC increases gradually.In the TC time,the subtropical trough is receding eastward,the boundary moves northward,the 200hPa wind field has an anticyclone circulation in the north of TC,200hPa Zonal Wind anomaly exhibiting a meridional wave train-like flow.Over the TC distribution region is easterly anomaly,farther north is westerly anomaly,TC create the poleward shift of the East Asian subtropical upper-level jet(EASJ).By EOF decomposition of TC track density,two significant modes and corresponding time coefficients are obtained,the corresponding spatial distribution are divided into four classes by time series,Philippines Sea pattern TC mainly distributes in the Philippine Sea and the southeast of Taiwan.Southeastern coast China pattern TC mainly distributes in Taiwan to the south of Japan,Philippines extends northwestly to the southeastern coast of China,Eastern Taiwan pattern TC mainly distributes in the east part of Taiwan and southern Japan,and the northeast of the Philippines,South China Sea pattern TC mainly distributes in the Philippines and the South China Sea.Interannual impact of TC in these distribution ranges is similar to climate state impact of TC,the significant difference is mainly in where TC passed,and the extent and area of anomaly are little different.When the TC distributes a wide range except the narrow coastal type TC distribution in the Southeastern coast China,the temperature in the north of the TC distribution is gradually weakening,and the negative anomaly on the ocean is gradually stretching westward.The geopotential height negative anomaly on the ocean in mid-high latitudes is gradually obvious.Positive anomaly in Eastern Taiwan TC pattern distributes from the ocean westward to the continent.WNP subtropical high when TC in the southeast coast of China is at the most westerly point at TC time,the subtropical position is the most easterly in Eastern Taiwan pattern in the TC time,which is consistent with the activity of TC.The Philippine Sea pattern and the Eastern Taiwan pattern TC can create the poleward shift of the westerly jet axis.However,when the TC distribution is southwest and the distribution scope is narrower,the influence to the westerly jet is weaker.There is a good correlation between East Asian summer monsoon and TC in summer.TC mainly weaken south-westly wind in Eastern China and JiangHuai region,and strengthen it around the Philippines.The relative vorticity anomaly in 850hPa caused by TC has good consistency with the intensity and location change of monsoon trough.