A general rule for synoptic-eddy feedback onto low-frequency flow

Abstract

In this study, scale interaction between synoptic eddies and low-frequency flow is investigated. It is demonstrated here that there is a general rule, the "left-hand rule", that describes synoptic eddy feedback onto low-frequency flow. The rule is that low-frequency anomalies systematically stir and deform the transient eddies in such a way that the irrotational eddy-vorticity fluxes are directed preferentially about 90A degrees toward the left-hand side of the low-frequency flow; thus this eddy feedback plays a positive role in maintaining and prolonging low-frequency flow under the stormy atmosphere. Similarly, we show that the irrotational eddy-temperature and moisture fluxes are also directed preferentially about 90A degrees toward the left-hand side of the low-frequency flow in the northern hemisphere. The eddy-temperature fluxes and their vertical structure play a positive role in reinforcing the low-frequency flow in the low levels. The moisture fluxes play a role in enhancing low-frequency flow by providing eddy-induced moisture convergence and divergence.