The Variability of the Oceanic Front in Kuroshio Extension and Its Relationship with the Pacific Storm Track in Winter

The intensity index of Kuroshio extension and its northern front zone (KEF) is defined as the area average of meridional SST (sea surface temperature) gradient by using Hadley Center's surface sea temperature dataset (1949-2014), and the Kuroshio extension frontal intensity index (KEFI) has seasonal and 10 a interdecadal variations. In winter, the KEFI has a significant positive correlation with the transient variance in the North Pacific storm track area, and the positive relationship appears when KEFI leads the storm track by one month, which indicates that the intensity of KEF can influence the storm track in winter, and KEFI would influence the subsequent storm track. Further investigations on the possible mechanism reveal that when the winter SST front is stronger, a more significant difference between ocean-air heat fluxes on both sides of the KEF can strengthen the near-surface temperature gradient, which is favorable for the maintenance of the near-surface baroclincity and the transient heat transport and eventually promotes the development of transient eddies. Additionally, the large-scale circulation is also affected by the KEF in winter. When the KEF is strong, the Aleutian Low deepens and the subtropical high strengthens; 500 hPa potential height increases (decreases) in the south (north), and the subtropical jet becomes weak but wide. It is found that the oceanic front promotes the development of the storm track by transporting heat upward and maintaining the air temperature gradient in winter.