The onset of the barotropic sudden warming in a global model

The barotropic, vortex-splitting sudden warming is analyzed in a simple global model, comprising the rotating shallow-water equations on the sphere with and without the effects of thermal forcing. A quasi-stationary approach is suggested as an effective means of exploring the two-dimensional parameter space of forcing amplitude and a suitable measure of vortex strength. We find that the main dynamical regimes obtained previously in a quasi-geostrophic f-plane model by Matthewman and Esler persist in the global model, with the exception of certain rotating vortex states that depend on the method of initialization. Short-lived regimes in which the vortex splits and reforms repeatedly are observed under certain parameters, although gradual dissipation of the vortex means that these cannot be classified as persistent vacillating states.