Wind stress curl variability over the North Pacific from the comprehensive ocean‐atmosphere data set

Abstract

Wind stress curl patterns over the north Pacific, between 3° and 55°N, are calculated from the Comprehensive Ocean‐Atmosphere Data Set (COADS). The mean wind stress curl pattern consists of a basin‐wide band of negative curl south of about 30°N and a basin‐wide band of positive curl to the north. Most of the variance lies in the northern half of the domain, associated with variability in the Aleutian low during winter. The dominant modes of variability are associated with the changes in position and intensity of the Aleutian low and the north Pacific (subtropical) high, each of which extends across the basin, the former in winter and the latter in summer. The seasonal signal accounts for about 40% of the variability in the region of the Aleutian low, about 30% of the variability in the northeast of the basin, and about 60% of the variability in the southwest of the basin between 20° and 30°N. The seasonal signal and first three nonseasonal empirical orthogonal functions (eofs) account for about 60% of the total variability in the mid‐latitude interior Pacific. The first eof represents variations in intensity of the Aleutian low, the second eof represents changes in intensity of the subtropical high and in the latitudinal position of the Aleutian low, and the third eof represents changes in the longitudinal position and orientation of the low. These three eofs together account for about 30% of the nonseasonal variability. On an interannual time scale, a negative (positive) wind stress curl anomaly in winter in the northeast often coincides with a positive (negative) SST anomaly in that region, although the relationship is far from perfect because of the importance of other mechanisms which influence SST variability. There is no distinct relationship between El Nino‐southern oscillation events and wind stress curl anomalies, although weak El Ninos seem to coincide with a positive wind stress curl anomaly across the central north Pacific.