Response of eddies to jet changes in an aquaplanet GCM

The position and low-frequency variability of the mid-latitude jets are dominated by interactions between the zonal-mean flow and the eddies. To isolate the response of the eddies, and of their momentum fluxes, to changes in the mean flow, we use a model setup in which the zonal-mean flow in an aquaplanet GCM is constrained without affecting the eddies.

When a shift of the mid-latitude jet is imposed, the eddy momentum flux response yields a positive feedback. The dominant mechanism seems to be a change of the direction of propagation of eddies, also apparent as changes in the dominant life-cycle. The impact of shifts in the critical latitude is confined to the subtropics. If the imposed anomalies are more baroclinic, an additional response from changes in low-level wave sources appears.

In the case of an imposed strenghtening and narrowing of the jet, the eddy feedback is negative, because less wave activity leaves the jet region.