Effects Of Intraseasonal Oscillation Of East Asian Zonal Wind Stream On Tropical Cyclone Landfall In Mainland China

Using,the ERA-Interim reanalysis datasets and the tropical cyclones(TC)best-track data from China Meteorological Administration during 1979-2015.By means of the filtering method,EOF method and synthesis analysis,the relationship between the East Asian zonal wind and the tropical cyclones landing in mainland China was analyzed in July and August.The results showed that:(1)The ISO of 200hPa zonal wind in subtropics and the mid-latitudes is very strong,especially in the south and north of zonal westerlies.According to the variance contribution and EOF typical space mode of the oscillation in high altitude zonal wind season,we defined the East Asian westerly index(EAWI)to describe the meridional move of the ISO of zonal westerlies.When the ISO of EAWI in negative anomaly,there are more TC landfall in the north of 22°N in mainland China,And vice versa.The environmental variables are also beneficial to the landing and maintenance of TC.There are southerly anomaly anomalous transient eddy vorticity flux over the exit region of the westerly jet in negative anomaly ISO of EAWI,which resulted in the weakening of westerly flow at the ISO of 200hPa.(2)The ISO of zonal wind has significant interannual relationship.In the weak year of ISO,the frequency of landing in tropical cyclone is significantly higher than that of the strong year of ISO,and the landing position is north and has a longer life history.In the weak:year of ISO,an easterly anomaly in the subtropical zone on the south side of the exit of the west wind jet is conducive to the landing of TC,and the vertical wind shear in the east is favorable to the maintenance of the landing TC.(3)During the interannual variation of TC,the contribution of the ISO and interannual variation to TC is different from that of the zonal wind.During the years of the TC low frequency,it is dominated by ISO of zonal wind,steering flow and vertical wind shear.However,during the years of the TC high frequency,no matter the contribution of the ISO or the contribution of interannual variation is very important.