Relationships between Sea Surface Temperature, the Atmospheric Circulation and Air-sea Fluxes on Multiple Time Scales

Abstract

The relationships of sea surface temperature (SST) anomalies with atmospheric general circulation and with momentum and heat fluxes are investigated in order to show the dominant structures in the North Pacific in the ENSO cycle (ES: 2-5 years) and decadal (DC: longer than 5 years) time scales, using newly computed monthly 5°×5° (longitude × latitude) gridded datasets for SST, wind stress, and net surface heating fields and National Meteorological Center (NMC) geopotential height data for the 40-year period of 1951-1990
The Pacific/North American (PNA) like pattern that has three centers in the 150°W-170°W longitudinal band in the wintertime 500hPa height field is prominent in the decadal changes of wintertime SST anomalies. Stronger (weaker) westerlies are located south (north) of the normal jet stream position during periods of below-normal (above-normal) SST anomalies in most of the entire extratropical North Pacific. Those SST anomalies are caused by the enhanced (suppressed) heat release along the Kuroshio and its extension, and by stronger (weaker) southward Ekman transport. However the dominant pattern of the wind field on the ES time scale is quite different from that on the DC time scale. The westerly jet in the central North Pacific is stronger than normal, but shifts northward of its mean position in years of ENSO warm episodes. On the other hand, the northwesterly wind is weaker, hence heat release is suppressed in the western North Pacific. A Western Pacific (WP) like pattern then appears in the atmospheric geopotential height field over the ocean with a below-normal center in the Bering Sea and an above-normal center south of Japan. The situation is reversed in the years of ENSO cold episodes.
The differences in the spatial patterns of SST anomalies on the DC and ES time scales are associated with differences in the atmospheric circulation, such as the predominance of PNA-like versus WP-like patterns. The corresponding change in the wind system then brings about a change of heat release and Ekman transport that form the SST anomalies. It appears that the distinctions between these two atmospheric patterns are responsible for the differences in the spatial structure of tropical SST anomalies on the DC and ES time scales.