Decadal and multidecadal North Atlantic SST anomalies driven by standing and propagating basin-scale atmospheric anomalies

Abstract

North Atlantic winter surface atmospheric circulation anomalies that vary over decadal and longer periods are characterized by examining the life history of individual anomaly features present from 1950 to 1992. Individual features observed on surface pressure anomaly (PA) maps propagated to the east-northeast during the early to mid-1950s and to the south from 1964 to 1984. Standing PA fluctuations were observed at other times. The nonstationary statistical properties of this atmospheric variability were not apparent in earlier studies because the statistical analysis techniques used assumed stationarity or assumed the atmosphere was dominated by standing patterns of variability. Observed winter sea surface temperature anomaly (SSTA) patterns that vary over decadal and longer periods were driven in part by these surface atmospheric anomalies through the associated anomalous surface turbulent heat flux patterns. The ocean tends to be anomalously cold (warm) where the surface wind speed is anomalously large (small). Local atmospheric forcing of winter SSTA remains important out to longer periods than previously realized. Although SSTA appears to respond passively to this atmospheric forcing, a complete understanding of the ocean-atmosphere variability documented here will require an understanding of processes responsible for driving the atmospheric circulation anomalies.