Abstract
Recent studies of observational data suggest that Sea Surface Temperature (SST) anomalies in the Atlantic Ocean have a significant influence on the atmospheric circulation in the Atlantic-European sector in early winter and in spring. After reviewing this work and showing that the spring signal is part of a global air-sea interaction, we analyze for comparison an ensemble of simulations with the ECHAM4 atmospheric general circulation model in T42 resolution forced by the observed distribution of SST and sea ice, and a simulation with the ECHAM4/OPA8 coupled model in T30 resolution. In the two cases, a significant influence of the Atlantic on the atmosphere is detected in the Atlantic-European sector. In the forced mode, ECHAM4 responds to SST anomalies from early spring to late summer, and also in early winter. The forcing involves SST anomalies not only in the tropical Atlantic, but also in the whole tropical band, suggesting a strong ENSO influence. The modeled signal resembles that seen in the observations in spring, but not in early winter. In the coupled mode, the Atlantic SST only has a significant influence on the atmosphere in summer. Although the SST anomaly is confined to the Atlantic, the summer signal shows some similarity with that seen in the forced simulations. However, there is no counterpart in the observations.
Highlights
Until recently, it had not been established from the observations whether Sea Surface Temperature (SST) anomalies in the North Atlantic have a significant effect on the North Atlantic Oscillation (NAO) and the other main atmospheric patterns in the AtlanticEuropean sector
The former argued that in HadAM2b the bulk of the oceanic influence was coming from the North Atlantic SST anomaly tripole, while the latter suggested that it was mostly coming from the tropical Pacific in ECHAM4
SST anomalies in the North Atlantic have a significant influence on the observed atmospheric circulation in the European-Atlantic sector in early winter and in spring
Summary
It had not been established from the observations whether SST anomalies in the North Atlantic have a significant effect on the North Atlantic Oscillation (NAO) and the other main atmospheric patterns in the AtlanticEuropean sector. The late spring atmospheric signal seemed to be primarily forced by SST anomalies in the tropical Atlantic, but it was not discussed in CF By using an ensemble of GCM simulations forced by global SST and sea-ice distribution during the last decades, Rodwell et al (1999) and Latif et al (2000), among others, were able to reproduce some of the low frequency variability of the NAO The former argued that in HadAM2b the bulk of the oceanic influence was coming from the North Atlantic SST anomaly tripole, while the latter suggested that it was mostly coming from the tropical Pacific in ECHAM4.
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