“…However, it is possible that the planetary-scale low-frequency waves extend the eddy-driven response even further polewards, meaning that their mutual interaction is important. It is also possible that transient eddy nonlinearities in the GCM act to extend the zonal mean wind anomalies polewards, in line with observations that link ENSO-induced changes in wave breaking to changes in the mean flow (Shapiro et al, 2001;Orlanski, 2003;Martius et al, 2007). Despite these differences, our results suggest that simple linear refraction can give rise to a positive wave-mean flow feedback in midlatitudes, which can explain a large part of the mean flow anomalies there, but that stationary wave anomalies and nonlinearities which are included in the GCM, but not in the QG model, are needed to fully account for the spreading of the positive U PAC anomalies to high latitudes during EN.…”