Interannual Positive Feedbacks in a Simple Extratropical Air–Sea Coupling System

Abstract

A simple theoretical analysis identified three possible interannual positive feedbacks in the extratropics: the upwelling mode, the SST-Sverdrup mode, and the SST-evaporation mode. The upwelling mode becomes unstable when the atmosphere responses to a warm SST anomaly predominantly with a high surface pressure. In contrast, the SST-Sverdrup mode is destabilized when the atmosphere responses to a warm SST with a low pressure. In the region of mean westerly wind, the SST-evaporation mode is unstable when the atmospheric response to a warm SST is a qurater-wavelength to the south. The upwelling mode seems to favor low-latitude regions, while the two SST modes seem to favor midhigh latitudes. It is suggested that the relative position of the stationary atmospheric response to anomalous SST is of crucial importance for the extratropical ocean-atmosphere interaction.