Topography-induced persistence of atmospheric patterns

Atmospheric blockings are persistent large-scale climate patterns with duration between days and weeks. In principle, blockings might involve a large number of modes interacting non-linearly, and a conclusive description for their onset and duration is still elusive. In this paper we introduce a simplified account for this phenomena by means of a single-triad of Rossby-Hawritz waves perturbed by one topography mode. It is shown that the dynamical features of persistent atmospheric patterns have zero measure in the phase space of an unperturbed triad, but such measure becomes finite for the perturbed dynamics. By this account we suggest that static inhomogeneities in the two-dimensional atmospheric layer are required for locking flow patterns in real space.