A kinematic mechanism for positive feedback between synoptic eddies and NAO

A kinematic mechanism for the positive feedback between the North Atlantic Oscillation (NAO) and synoptic eddies are depicted based on observational data analyses. Using three-point rescaled covariance statistics of band-pass-filtered (2-8 days) synoptic eddy fields, we examined observed eddy structure changes associated with winter-mean NAO anomalous flow. It is demonstrated that the NAO flow anomalies systematically deform the structures of recurring synoptic eddies to generate seasonal-mean eddy-vorticity flux anomalies predominately directed to the left-hand side of the NAO flow anomalies. These anomalous eddy-vorticity fluxes converge into the cyclonic center and diverge from the anticyclonic center of the anomalous NAO flow, and thus enhance the NAO flow. Citation: Ren, H.-L., F.-F. Jin, J.-S. Kug, J.-X. Zhao, and J. Park (2009), A kinematic mechanism for positive feedback between synoptic eddies and NAO, Geophys. Res. Lett., 36, L11709, doi:10.1029/2009GL037294.