A Simple Model of Wave-Mean Flow Feedbacks, Poleward Jet Shifts and the Annular Mode

A simple mechanistic model explaining the effect of the zonal-mean flow anomalies on the eddy momentum fluxes is described. The model reproduces the wave-mean flow feedbacks that maintain the annular mode, cause stronger jets to shift poleward (and vice versa), and cause the poleward propagation of zonal wind anomalies (particularly those out of phase with the annular mode). In the model, the effect of the mean flow on the eddy momentum fluxes is determined solely by (1) the critical level and (2) the reflecting level (reflecting level = the locus of turning latitudes). There is no "baroclinic" feedback. The model is used to distill the essential dynamics of annular variability and change.