Changes in the relationship in the SST variability between the tropical Pacific and the North Pacific across the 1998/1999 regime shift

Abstract

This study shows that sea surface temperature (SST) variability in the central to eastern tropical Pacific has a strong negative correlation with that of the central to eastern North Pacific in the boreal winter after the 1998/1999 regime shift. This phenomenon is in contrast to before the 1998/1999 regime shift. The anomalous Aleutian low pressure associated with the tropical SST forcing became stronger, and its center shifted to the south and to the west after 1998/1999. Such a modulation caused the change in the North Pacific SST response. This also resulted in a close relationship between the tropical Pacific and North Pacific SST variability. The modulation of the Aleutian low pressure is primarily due to the westward shift in the location of the tropical convective heating around the dateline, which occurred during 1998/1999. The results of simple atmospheric model experiments support this hypothesis that the shift in the tropical convective heating to the west is responsible for the modulation of the Aleutian low pressure and the associated change in the relationship of the SST variability between the tropical Pacific and North Pacific. These results imply that the seasonal predictability of the North Pacific SST has increased since 1998/1999 due to its increased correlation with the tropical Pacific SST variability.