The asymptotic theory of the generation of long-wave structures in critical layers of weakly dissipative jet flows

Abstract

The mechanisms of the large-scale vortex structures formation in zonal jet flows (atmospheric blockings, cyclonic, and anticyclonic vortices) is investigated. Nonlinear perturbations formed during the onset of barotropic instability of a long-wave mode in weakly-dissipative and weakly supercritical jet flows with a symmetric velocity profile are considered in the β-plane approximation. This analysis is performed within the framework of the asymptotic theory based on the concept of a nonlinear critical layer. The equations describing the interaction of a wave with vorticity perturbations in a critical layer are derived. The regimes of a quasi-stationary and nonstationary nonlinear critical layer are considered separately. Combined equations of evolution covering the principle regimes of instability development are proposed. The existence of autowave-type structures characterized by a balance between the energy receipt to the wave and its dissipation are obtained within the framework of a numerical simulation. The dependence of the parameters of generated autowave structures on the shape of the zonal jet profile and the flow supercriticality level is studied.