The Influence of Large-Scale Topography on Barotropic Vortex Motion

Abstract

The motion of a barotropic vortex in the vicinity of a large-scale topographic feature is examined through numerical integration of the shallow-water equations in an equatorial beta-plane channel. The topographic parameters are chosen to represent the Sierra Madre mountains of Mexico. The motion of the vortex is affected through modification of the asymmetric circulation by vortex stretching associated with divergence of the horizontal velocity field as the air flows across the mountain. A vortex that approaches the topography from the east is accelerated and deflected toward the south and a vortex initially west of the mountain recurves and moves toward the cut. This motion is in contrast to the northwestward motion of a vortex over level terrain. The vortex motion is also compared to the direction of the imposed potential vorticity gradient. The topographic effects described in this paper may be important in forecasting hurricane motion in the eastern North Pacific and western Gulf of Mexico.