Relationship Between Oceanic Fronts In Kuroshio Extension Area And North Pacific Storm Tracks And Its Climatic Effect

There are significant sea surface temperature(SST)gradient in Kuroshio Extension(KE)sea area,the remarkable effects on the atmospheric boundary layer and even the upper troposphere has been investigated.On this basis,this study analysis the distribution characteristics and seasonal changes of SST meridianal gradients in KE sea area,and defines the area average of maximum gradient zone as an intensity index of KE fronts(Kuroshio Extension Fronts Index,KEFI),then investigates its interannual and decadal variations.The middle and upper troposphere in the North Pacific is mainly realized as transient disturbances,and there is a certain coupling relationship with the oceanic fronts variation in the KE sea area.It is found that there is a significant positive correlation between transient disturbances and KEFI in the North Pacific,especially in the main body of storm tracks.The storm tracks would strengthen as well as the KE fronts,and the relationship is evident when the KEFI lead storm tracks a month.The possible mechanism of this effect was studied: when the winter SST front is stronger,the more significant difference between ocean-air heat flux in both sides of KEF could strengthen the near-surface temperature gradients,which maintains the near-surface baroclincity and benefits the transient heat transport polewards,promote the develop of transient eddies at last.Additional,the large-scale circulation also be response to KEF in winter: when the KEF is stronger,the Aleutian is deepen,the subtropical high is strengthen,the 500 hPa potential high is increased(decreased)in south(north),the subtropical jet is weaker and wider.The change of KEFI also has some influence on the climate change in North America and East Asia.A strong(weak)KE front anomaly in autumn is associated with an increasing(decreasing)surface temperature over western North America but a decreasing(increasing)surface temperature over eastern North America.In winter,central North America warms(cools)when the KE front is strong(weak).The response of the atmospheric circulation,including wind in the high and low troposphere,troughs,and ridges,to the strengthening(weakening)of the KE front is the main cause of these changes in surface temperature.In addition,the oceanic fronts intensity in KE sea area has a synchronic effect on East Asian temperatures during the winter and spring season,and this effect could last until the next season.In winter,when the KE fronts is strong,the temperatures in eastern and southern East Asia would increase in the same period,northern and northeastern region temperatures would rise in next spring.The effect is due to the enhancement of jet which is not conductive to cold air southwards.The strengthen of KE fronts in spring also raised the temperatures in eastern and southern East Asia,as well as the temperatures of northwestern and northern China in summer.The main reason for this effect is the neighborhood response of the East Asian temperatures to the anomalous changes of the upstream Kuroshio during the same period,and this effect lasts until the summer.