Arctic oscillation and corresponding sea surface temperature anomaly fields

Empirical orthogonal function (EOF) and rotated EOF analyses of the monthly mean sea level pressure (SLP) anomalies reveal that the Arctic Oscillation (AO) activities include those of both the North Atlantic Oscillation (NAO) and the Polar-Eurasia pattern (POL). However it is found that the NAO and the POL are not independent of each other. Based on a regression analysis, it is also found that the organized sea surface temperature (SST) anomaly fields coherently varying with the AO exist in the North Atlantic and the North Pacific. EOF analysis is also applied to the monthly mean SST anomaly fields in the region north of 20 degree N. The mode closely relating to the AO appears as the second EOF mode. On the other hand, the first mode reveals a strong decadal fluctuation correlated with the activities of the Pacific/North American (PNA) pattern. The AO index shows a significant jump in 1988/89. This climate jump appears clearly in the second SST-EOF mode (i.e., AO) and partially in the first SST-EOF mode (i.e., PNA). In contrast, the well-known climate jump occurring in 1976/77 is obseved only in the first SST-EOF mode.