Observed Impact of Atlantic SST Anomalies on the North Atlantic Oscillation

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Abstract
The large-scale patterns of covariability between monthly sea surface temperature (SST) and 500-mb height anomalies (Z500) in the Atlantic sector are investigated as a function of time lag in the NCEP–NCAR reanalysis (1958–97). In agreement with previous studies, the dominant signal is the atmospheric forcing of SST anomalies, but statistically significant covariances are also found when SST leads Z500 by several months. In winter, a Pan-Atlantic SST pattern precedes the North Atlantic oscillation (NAO) by up to 6 months. Such long lead time covariance is interpreted in the framework of the stochastic climate model, reflecting the forcing of the NAO by persistent Atlantic SST anomalies. A separate analysis of midlatitudes (20°–70°N) and tropical (20°S–20°N) SST anomalies reveals that the bulk of the NAO signal comes from the midlatitudes. A dipolar anomaly, with warm SST southeast of Newfoundland and cold SST to the northeast and southeast, precedes a positive phase of the NAO, and it should prov... Abstract The large-scale patterns of covariability between monthly sea surface temperature (SST) and 500-mb height anomalies (Z500) in the Atlantic sector are investigated as a function of time lag in the NCEP–NCAR reanalysis (1958–97). In agreement with previous studies, the dominant signal is the atmospheric forcing of SST anomalies, but statistically significant covariances are also found when SST leads Z500 by several months. In winter, a Pan-Atlantic SST pattern precedes the North Atlantic oscillation (NAO) by up to 6 months. Such long lead time covariance is interpreted in the framework of the stochastic climate model, reflecting the forcing of the NAO by persistent Atlantic SST anomalies. A separate analysis of midlatitudes (20°–70°N) and tropical (20°S–20°N) SST anomalies reveals that the bulk of the NAO signal comes from the midlatitudes. A dipolar anomaly, with warm SST southeast of Newfoundland and cold SST to the northeast and southeast, precedes a positive phase of the NAO, and it should prov...