Interaction between synoptic eddy and low-frequency flow (SELF) has been a subject of manystudies. In this study, we further examine this interaction by introducing a transformed eddy-potential-vorticity(TEPV) flux that is obtained from eddy-potential-vorticity flux through a quasi-geostrophic potential-vorticityinversion. This TEPV flux combines the effects of the eddy-vorticity and heat fluxes into the net acceleration of thelow-frequency flow. We show that the anomalous TEPV fluxes are preferentially directed to the left-hand side ofthe low-frequency flow in all vertical levels throughout the troposphere for monthly flow anomalies and for climatemodes such as the Arctic Oscillation (AO). Furthermore, this left-hand preference of the TEPV flux direction is asimple indicator of the positive reinforcement of the low-frequency flow by net eddy-induced acceleration. Byprojecting the eddy-induced net accelerations onto the low-frequency flow anomalies, we estimated the eddyinducedgrowth rates for the low-frequency flow anomalies. This positive eddy-induced growth rate is larger(smaller) in the lower (upper) troposphere. The stronger positive eddy feedback in the lower troposphere may playan important role in maintaining an equivalent barotropic structure of the low-frequency atmospheric flow bybalancing off some of the strong damping from surface friction.
展开▼
