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.