Eddy-induced poleward migration of westerly jets in an idealized atmospheric global circulation model

Abstract

This thesis work tests the hypothesis that synoptic eddy and low-frequency flow (SELF) feedback may result in the slow poleward migration of a zonal jet. An atmospheric general circulation model (GCM) was integrated without forcing or dissipation under a basic state in each hemisphere consisting of a single, baroclinically unstable, zonally-uniform jet centered on 30° or 45° latitude. For a wide range of jet speeds, the jet was found to sharpen and jump poleward initially, as the result of the rapid development of synoptic baroclinic eddies due to baroclinic instability. After the end of the initial eddy life cycles, the jet migrated slowly poleward. A preliminary, diagnostic investigation shows that this second type of behavior is consistent with a hypothesis based on the theoretical framework of the SELF feedback (Jin et al. 2006a). Furthermore, the relationship between the speed of poleward propagation and the ratio of eddy momentum fluxes to the background zonal flow is in good agreement with theoretical predictions. The physics involved may also apply to migrating zonalwind anomalies of the type observed in the simulations of more complex GCMs and in nature.