---
bibliography:
- 'eddy\_clean.bib'
title: 'Quantifying the eddy-jet feedback strength of the annular mode in an idealized GCM and reanalysis data'
---

Introduction
============

The annular mode is a dominant mode of variability of the extratropical circulation in both hemispheres on intraseasonal to interannual timescales [@Kidson1988; @Thompson1998; @Gong1999; @Thompson2000]. The annular mode corresponds to the leading empirical orthogonal function (EOF) of zonal mean zonal wind, which features an equivalent barotropic dipolar structure and represents latitudinal shifts of the eddy-driven midlatitude jet [@Nigam1990; @Hartmann1998; @Thompson2014; @Thompson2015]. The zonal index, the time series associated with the annular mode, is essentially the same concept as that discussed in the pioneering studies of the variability of the general circulation [@Rossby1939; @Namias1950; @Wallace1985]. The annular mode in the Northern Hemisphere is often considered in recent studies as the hemispheric manifestation of the North Atlantic Oscillation [e.g., @Wallace2000; @Vallis2004]. The annular mode is characterized by temporal persistence [@Baldwin2003; @Gerber2008a; @Gerber2008b], for which it has been suggested that a positive feedback between anomalous zonal flow and eddy fluxes is responsible [e.g., @Feldstein1998; @Robinson2000; @Gerber2006; @Lorenz2001 hereafter, LH01]. For example, @Robinson2000 suggested that at the latitudes of a positive anomaly of barotropic zonal wind, while surface drag tends 