We thank the two anonymous reviewers for their constructive comments and suggestions, which led to an improvement of the manuscript. This study was supported by the National Natural Science Foundation of China under Grants 41005028 and 40730953. GC was supported by the US NSF Grant AGS-1064079.
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A linear instability analysis, a method similar to that in Solomon and Stone (2001), has been carried out on the equilibrium states in the sensitivity runs. For all of the zonal mean states in the sensitivity runs, zonal wavenumbers 6 and 5 are the two linearly most unstable modes.
To display the contribution from each zonal wavenumber, different from Randel and Held (1991), the spectra are not smoothed by any spectral window.
As in Chen and Plumb (2009), the strength of the eddy feedback also varies with the friction. In our sensitivity runs, the correlations are reduced with enhanced surface friction.
For the zonally averaged eddy heat flux and the lower-level temperature gradient, their first EOF all represents a pulsing of their intensity associated with the eddy life cycle, whose distributions are not shown here.
In the upper levels, with strong U − Cr, waves can propagate meridionally throughout the jet center with little decay. Thus, the two groups of eddies from wavenumber 4, which are generated at the jet flanks and propagate into the jet from opposite directions, can cancel each other at the jet center, resulting in weaker jet deceleration there.
The results of the regression analysis are also supported by the composites of the eddy heat flux, eddy forcings, and critical line distributions of the two zonal wavenumbers in the positive and negative phases of the annular modes. The most significant variation between the two phases is the latitudinal shift of the whole system.