Eliassen-Palm Flux Diagnostics and the Effect of the Mean Wind on Planetary Wave Propagation for an Observed Sudden Stratospheric Warming

Abstract

Eliassen-Palm (E-P) flux whose direction is interpreted as that of planetary wave propagation in the meridional plane, is used for diagnosing planetary waves for the 1973 sudden stratospheric warming. E-P flux by zonal wavenumber 1 component was focused into the polar stratosphere prior to the circulation reversal. By the focusing there occurred the intense convergence of E-P flux which embodies the forcing of waves on mean flow. The convergence brought about the intense deceleration of mean zonal wind and the poleward residual mean meridional flow in the stratosphere.
A discussion is made of the "refractive index" Q defined as mean quasi-geostrophic potential vorticity gradient divided by mean zonal wind. It is the maximum of Q which was situated in the polar stratosphere prior to the warming that is interpreted as a main factor which determines the switching of E-P flux from equatorward to poleward. After the easterly winds appeared in the polar stratosphere the convergence of E-P flux concentrated around the zero wind line, suggesting that the mechanism of critical layer absorption was driven.