Causes of low frequency North Atlantic SST variability in a coupled GCM

The relative roles of stable and unstable coupled feedbacks in inducing the low frequency SST variability in various regions of the North Atlantic are studied using a coupled general circulation model. The interactive ensemble technique is applied to reduce the strength of "weather noise" in the model and isolate the atmospheric feedback to boundary forcing. We find that the low frequency SST variability in the subtropical North Atlantic is mainly induced by stable coupled feedbacks in which the weather noise plays a central role. However, in the Gulf Stream extension area, the SST variability may be attributed to processes internal to the ocean. Although the results are not definitive, there is no compelling evidence that unstable coupled feedbacks are important for low frequency SST variability in the North Atlantic in this model.