NUMERICAL STUDY OF THE NONLINEAR ROSSBY WAVE CRITICAL LEVEL DEVELOPMENT IN A BAROTROPIC ZONAL FLOW.

Abstract

The fully nonlinear barotropic vorticity equation is integrated in time to study the development of a Rossby wave critical level. The initial conditions consist of a hyperbolic tangent shear flow and a steady forced wave at the northern boundary; a radiation condition is used at the southern boundary. Linear, quasi-linear and nonlinear integrations are made, and the results are compared with previous studies. For small values of the perturbation amplitude, such that nonlinear interactions are important only in the critical layer, a steady state is obtained in the outer domain, in which the Reynolds stress vanishes both above and below the critical level, and the forced wave is totally reflected. Some conclusions are drawn with respect to the forcing of the equatorial regions by meridionally propagating midlatitude Rossby waves.