Analysis on SST Anomaly Structure in the Kuroshio Extension in Winter and Its Relationship to Tropical Pacific SST Variation

Based on the high-resolution SST dataset from 2003 to 2015 provided by the remote sensing system of NASA, the possible relationship between wintertime SST anomaly (SSTA) characteristics over the Kuroshio Extension in the North Pacific and tropical SST is investigated in this study. The methods used include empirical orthogonal function analysis and time-lagged correlation analysis, etc. The results show that the wintertime SSTA over the Kuroshio Extension presents two types of structural characteristics, i.e., the type of upstream area development and the type of zonal extension. The latter involves two zonal expansion modes with the bifurcation structure and the channeling structure, respectively. The two expansion modes are in opposite phase and in the same phase before and after 2010, respectively. The eastward extension of the warm anomalies was limited to the south of 36°N before 2006, whereas the extension shifted to the northern path during 2006 to 2010 and after 2010. The bifurcation extending mode are closely related to tropical SST variation. Further studies by time-lag correlation analysis and composite analysis indicate diverse impacts on the bifurcation mode of SST over different regions in the tropical Pacific. Niño3 SST index led the bifurcation mode over the Kuroshio Extension SSTA by 1-2 months, while Niño3.4 and Niño4 indexes are correlated with the bifurcation mode at a lead and lag of 3-month respectively, which indicates that the eastern type and central type of El Niño may have the lead and concurrent correlation relationships with the bifurcation mode, respectively, and the latter is more remarkable.