Changes in the relationship in the SST variability between the tropical Pacific and the North Pacific across 1998/99 regime shift

Abstract:

This study examines why the relationship in the sea surface temperature (SST) variability between the tropical Pacific and the North Pacific during the boreal winter (Dec.-Jan.) has been changed across the 1998/99 regime shift. While, the SST variability in the central-to-eastern tropical Pacific is highly negatively correlated with that in the central-to-eastern North Pacific after the 1998/99 regime shift, it is not before the 1998/99 regime shift. It is found that the anomalous Aleutian low pressure in response to the tropical SST forcing becomes stronger and its center is shifted to the south and to the west after the 1998/99 to regime shift, which plays a key role to tighten the relationship in the tropical Pacific-North Pacific SST variability. Such a modulation of Aleutian low pressure is mainly due to the location of tropical heating, which is shifted to the west around the dateline in the tropical Pacific across the 1998/99 regime shift. Simple atmospheric model experiments also support this hypothesis that the shift of tropical heating to the west is responsible for strengthening the relationship in the tropical Pacific-North Pacific SST variability via the modulation of atmospheric teleconnections.