The reemergence of the winter sea surface temperature tripole in the North Atlantic from ocean reanalysis data Climate Dynamics

Multiple ocean reanalyses and objective analyses are used to study the reemergence of the large–scale pattern of winter sea surface temperature anomalies (SSTAs) in the North Atlantic (15° N–70° N 80° W–8° W). The dominant SSTA pattern in winter forms under the North Atlantic Oscillation forcing and have a tripole structure with anomalies of one sign in the subtropics and the opposite sign in the tropics and high latitudes. Empirical orthogonal function (EOF) analysis indicates that the dominant mode of interannual variability in the summer seasonal thermocline (~ 65–90 m in August–September) also has a tripole structure. The reemergence mechanism is evaluated by correlating the time series of the leading pattern of ocean temperature anomalies in the summer seasonal thermocline with SSTAs over the course of the year. It is shown that the tripole in the summer seasonal thermocline is most strongly related to SSTAs in the previous March–April (explains ~ 15% of the variance), when the upper mixed layer (UML) of the North Atlantic is deepest. During summer, the SSTA variance explained by this EOF decreases, reaching a minimum of 5–6% in August–September. With the UML deepening in the subsequent autumn–winter, this value increases, reaching two–thirds of the initial signal.