Zonal-eddy coupling and a neutral mode theory for the Arctic Oscillation

This study demonstrates that a dynamical mode that resembles the observed A rctic Oscillation (AO) pattern can be obtained as a least damped the mode o f a linear operator that expresses the dynamics of the zonally averaged flo w interacting with stationary, zonally-asymmetric waves. The spatial patter n of the leading singular mode of the operator bears much resemblance to th e observed Arctic Oscillation both in terms of zonal and associated wave co mponents. The mode has a damping time scale of more than a month, and is we ll separated from subsequent modes. Therefore, it is plausible that it surv ives on monthly and and longer time scales. The simulated zonally asymmetri c waves produce a meridional tilt due to advection by the, AO-like sheared zonal flow and positively feed back to the zonal flow through the momentum flux arising from the interplay with the climatological mean waves. The dom inant contribution of this feedback is shown to come from the features in t he North Atlantic sector, supporting the notion that the AO is a hemispheri c extension of the more regional North Atlantic Oscillation.