Dissimilar characteristics associated with the 1976/1977 and 1998/1999 climate regime shifts in the North Pacific

Abstract

We examined dissimilar characteristics associated with the North Pacific mean sea surface temperature (SST) regime shifts across 1976/1977 and 1998/1999. The SST spatial pattern across 1976/1977 was more similar to that of a Pacific Decadal Oscillation compared with that across 1998/1999. Across the 1976/1977 regime shift, the wind stress curl forcing before 1976/1977 was not balanced with meridional oceanic currents after 1976/1977, indicating that the oceanic dynamic adjustment due to basin-scale anomalous wind forcing in the North Pacific played a minor role in the 1976/1977 climate regime shift. However, the atmospheric forcing significantly contributed to the SST condition after the 1976/1977 regime shift. On the other hand, both oceanic dynamic adjustment and atmospheric wind forcing played key roles in the 1998/1999 North Pacific regime shift. We infer that the leading mechanisms associated with the North Pacific SST regime shift depend on the change of mean SST over the tropical Pacific.