Spatial Patterns of Atmosphere-Ocean Interaction in the Northern Winter

Abstract

The variability of monthly mean sea-surface temperature (SST) anomalies over the extratropical North Atlantic and Pacific and its relation to atmospheric circulation anomalies over the Northern Hemisphere during wintertime is investigated, by applying eigenvector analysis to a 39-year dataset and correlating the time series of the resulting expansion coefficients with the hemispheric 500 mb height and sea-level pressure fields. In agreement with previous studies, the simultaneous correlation between the tone series of the expansion coefficient of the first empirical orthogonal function (EOF 1) of North Pacific sea surface temperature (SST) and the hemispheric 500 mb height field resembles the Pacific/North American pattern, and the corresponding pattern for Atlantic SST resembles the North Atlantic Oscillation. In the vicinity of the conters of action of thew patterns, the SST fluctuations associated with these modes explain on the order of half the variance of 500 mb height and slightly less of the variance of the associated ma-level pressure fluctuations. Analogous calculations were performed on the anomalous midwinter SST tendency, defined as the SST anomalies averaged from February through April minus the SST anomalies averaged from October through December of the previous calendar year. The leading EOF's of SST tendency in both oceans exhibit distinctive “sandwich” patterns, with bands anomalies of one polarity over the western ocean centered near 30°–35°N, flanked by anomalies of the opposite polarity over the northern oceans near 50°N and in the subtropics, new 15°N. EOF 1 of North Atlantic SST tendency is more robust than its counterpart for SST itself. The correlation between the time series of the expansion coefficient of EOF 1 of North Pacific SST tendency and the hemispheric 500 mb height field resembles the western Pacific pattern, and the corresponding pattern for Atlantic SST resembles the western Atlantic pattern, as defined by Wallace and Gutzler. “High zonal index” atmospheric circulation patterns in winter [i.e., strong anticyclones new 30°N, strong westerlies along 50°N, and strong tradewinds] are observed in association with anomalous warming of the ocean in the anticyclone belt and cooling in the westerly and tradewind belts. It is suggested that these patterns are particularly effective in modulating the fluxes of latent and sensible heat at the air-sea interface and wind-driven vertical mixing and entrainment through their influence upon surface wind speed. Received: July 1, 1989; Accepted: March 20, 1990