Midlatitude ocean-atmosphere interaction in an idealized coupled model

Interannual-to-interdecadal ocean-atmosphere interaction in midlatitudes is studied using an idealized coupled model consisting of high resolution two-layer quasigeostrophic oceanic and atmospheric components with a simple diagnostic oceanic mixed layer.

The leading mode of atmospheric low-frequency variability is equivalent barotropic and involves localized intermittent highs and lows of atmospheric pressure situated over the ocean. This pattern does not seem to be affected by an oceanic coupling.

The spatial and temporal structure of the atmospheric intrinsic variability determines the oceanic variability on both regional and basin scale. The former is characterized by a delayed modulation of the baroclinic time-dependent circulation in response to the atmospheric forcing. The first basin scale EOF of SST is similar in structure to the interdecadal mode found by Kushnir (1994). A warm SST anomaly is accompanied by the anomalous atmospheric low pressure and intensified model Gulf Stream.

In the western part of the ocean, this pattern is forced by the atmospheric pressure anomaly through its influence on the geostrophic ocean circulation. The anomalous currents advect mean SST in the mixed layer and produce the SST anomaly described above.