The Antarctic stratospheric sudden warming of 2002: A selftuned resonance?, Geophys

The extraordinary Antarctic stratospheric warming event of 2002 was characterized by a remarkable vertical structure, with the vortex observed to divide at upper levels in the stratosphere but not at lower levels: such ‘partially ’ split vortex events are relatively rare. A simple, yet fully three-dimensional, model is constructed to investigate the dynam-ics of this unique event. Planetary waves are excited on the model vortex edge by a lower boundary forcing character-ized by two parameters: an amplitude hF and a frequency ωF, measured relative to a stationary frame. For realistic forcing amplitudes, a partial vortex split resembling that observed during the 2002 event is found only within a spe-cific, narrow band of forcing frequencies. Exploiting the relative simplicity of our model, these frequencies are shown to be those causing a ‘self-tuning ’ resonant excitation of the gravest linear mode, during which nonlinear feedback causes an initially off-resonant forcing to approach resonance. 1