Maintenance of decadal SST anomalies in the midlatitude North Pacific

Abstract

Mechanisms that maintain decadal sea surface temperature (SST) anomalies in the midlatitudes North Pacific are investigated using observational data. Focussing on the seasonality of decadal SST anomalies, individual heat budget analyses were conducted for the ocean mixed layer in a southern region (25°N-35°N, 175°E-145°W , and a northern region (39°N-49°N, 165°E-155°W) of the North Pacific. It was revealed that the decadal SST anomaly in the southern region, which was pronounced in winter, was significantly maintained by meridional Ekman temperature advection that occurred during November-January. On the other hand, the decadal SST anomaly in the northern region, which was observed in almost all months, was maintained by the sum of the effects of sensible and latent heat flux, and the net long wave radiation flux at the sea surface, and the meridional Ekman temperature transport during the period of October-December. In the Kuroshio extension region, which overlaps the southwest portion of the northern region, the anomalous temperature transport by entrainment in the seasonal thermocline was found to be very important for the maintenance of decadal SST anomaly.