Quasi-Decadal Variation in Intensity of the Western Part of the Winter Subarctic SST Front in the Western North Pacific: The Influence of Kuroshio Extension Path State

Abstract

Abstract Variations of the subarctic front (SAF), which is extracted as a strong sea surface temperature (SST) gradient in the longitudinal band of 146°–152°E, were investigated over 30 winters (January–March) from 1982 to 2011, using high-spatial-resolution satellite-derived SST dataset and hydrographic observations. The SAF had little meridional movement in this longitudinal band, lying between 40° and 41°N throughout the analysis period. The SAF intensity had a dominant quasi-decadal time scale (about 8 yr); its intensity in the strong phase was up to about 50% higher than in the weak phase. The SAF intensity strongly reflected upper-ocean conditions in the Kuroshio–Oyashio Confluence (KOC) region just south of the SAF. In the strong SAF phase, large positive anomalies in both temperature and salinity were found in the KOC region, not only at the sea surface but also below 300 m, and the water properties in the KOC region were those of the Kuroshio water. The warm, salty water in the KOC region was supplied by mesoscale eddies, which detached northward from the Kuroshio Extension during the unstable state of the Kuroshio Extension path.