Position And Intensity Variability Of The Kuroshio Extension Sea Surface Temperature Front

Based on high spatial resolution sea surface temperature(SST)satellite data from 1993-2013,we studied the Kuroshio Extension sea surface temperature Front(KEF)from 141°E to 158°E and described the seasonal,monthly and interannual-to-decadal variations of KEF position and intensity.According to the research of KEF position,we noticed that the latitudinal positions of KEF vary with longitudes.The western part of KEF from 141°E to 144°E is relatively stable,whereas the eastern part from 153°E to 158°E exhibits the largest amplitude of its north-south displacement.Further analysis reveals that the position of western KEF(KEFw,141-144°E)is dominated by the decadal variability,while the positions of central KEF(KEFc,144-153°E)and eastern KEF(KEFe,153-158°E)change significantly both on interannual time scale and on decadal time scale.In addition,the KEFw position is well correlated with the KEF path length.We also indicated that the KEFw position exhibits significant connections with the Pacific Decadal Oscillation(PDO)index and North Pacific Gyre Oscillation(NPGO)index with the time lag of 40 months and 33 months,respectively.The result of monthly variability of KEF intensity shows that the KEF is seasonally strongest in winter and weakest in summer and its intensity is similar in spring and in autumn.Particularly,the KEF is strongest in January,and frontolysis occurs in February and last until August when the KEF becomes weakest,then frontogenesis occurs in September.The KEF is strongest near 142°E then becomes weaker eastward.The monthly variations of KEF intensity vary with longitudes.The amplitude of monthly KEF intensity variation is largest near the Japan coast(141-145°E),and decreases eastward.Furthermore,a diagnosis based on a simple mixed-layer model was used to investigate the monthly variation of KEF intensity.The result revealed that the monthly variation of KEF intensity is mainly induced by atmospheric forcing.The meridional gradient of net heat flux causes the monthly strengthening and weakening of KEF.As for the interannual variability of KEF intensity,we found that it varies both with longitudes and seasons.The amplitude of interannual KEF intensity variation is largest near the Japan coast(141-145°E),and decreases eastward.The amplitude of the interannual KEF intensity variation is largest in winter,followed by that in spring and in autumn,and in summer the amplitude of the interannual variation of KEF intensity is smallest.We also noticed that the KEF intensity has not only a 1-yr period variation,but also a 2-yr one.The interannual variability of KEF intensity is dominated by KE states,which is different from the monthly variability of KEF intensity.When the KE meanders the KEF is weak and it is strong when the KE path is straight.Surprisingly,we found that the KEF has a long-term strengthening trend from 1993 to 2014,especially the averaged intensity in winter.This strengthening trend is most evident near the Japan coast(141-145°E),but for 152-158°E,the KEF does not have a significant strengthening trend.An Empirical Mode Decomposition was used to separate a long-term trend from the KEF intensity time series during 1993-2014.And this long-term strengthening trend of KEF is suggested to be possibly related with the long-term shortening of KE path.