Barotropic decelerations of the southern stratospheric polar vortex

Abstract

The northern and southern polar vortices are subject to quite different dynamical forcings, with the variability of the northern polar vortex much more dominated by baroclinic wave processes. Some recent works describe a barotropic structure in vortex‐splitting sudden stratospheric warming events (SSWs). Performing an analysis of the anomalies of the energy cycle, we show that strong decelerations of the southern polar vortex are, in fact, dominated by the transfer of kinetic energy between barotropic components. A major role is played by the barotropic zonal wave number n = 3 in the energy transfer of kinetic energy. This result, conjugated with the fact that stationary tropospheric waves in the southern midlatitudes have an amplitude peak at zonal wave number n = 3, suggests that the barotropic mechanism of ‘nonlinear resonance tuning’ may be the cause of strong decelerations of the southern stratospheric polar vortex.