An Eddy–Zonal Flow Feedback Model for Propagating Annular Modes

Abstract The variability of the zonal-mean large-scale extratropical circulation is often studied using individual modes obtained from empirical orthogonal function (EOF) analyses. prevailing reduced-order model leading EOF (EOF1) zonal wind, called annular mode, consists an eddy–mean flow interaction mechanism that results in a positive feedback EOF1 onto itself. However, few studies have pointed out under some circumstances observations and GCMs, strong couplings exist between EOF2 at lag times, resulting decaying-oscillatory, or propagating, modes. Here, we introduce for coupled accounts potential cross-EOF eddy–zonal feedbacks. Using analytical solution this model, derive conditions existence propagating regime based on strengths. idealized GCMs stochastic prototypes, show feedbacks play important role controlling persistence by setting frequency oscillation. We find stronger lead to less persistent Applying coupled-EOF Southern Hemisphere reanalysis data shows highlight importance considering coupling EOFs fully understand natural forced circulation.