Evolution of a Rossby Wave Packet in Barotropic Flows with Asymmetric Basic Current, Topography and δ-Effect

Abstract

Using the Rossby wave packet approximation and the WKB method, the evolution of a single geostrophic synoptic disturbance has been studied. The structural changes of the wave packet due to the variation of β with latitude, the asymmetric basic currents and the variety of topography are thoroughly discussed. However, there are different effects on the wave packet in the various asymmetric basic currents, depending on the different positions of the wave packet relative to the basic current and the variety of topography. The δ-effect always lengthens the Rossby wave packet's longitudinal scale and causes the westward-tilting trough line to lean toward the Y-axis, i.e., to the north. When the Rossby wave packet is located to the left (right) side of a southwesterly jet its longitudinal scale (latitudinal scale) will lengthen and its latitudinal scale (longitudinal scale) will shrink, while the westward-tilting trough line will become more westward (toward the Y-axis). Linearly sloping topographies will not affect the structure of the Rossby wave packet, but nonlinear topographies do affect the structure of the packet. The results suggest that the mountains, especially the Rocky Mountains, may decrease (increase) the X-propagating disturbance system when it is westward- (eastward) tilted. The effects of topography on distributions of east-west oriented, north-south oriented, convex and concave models have been discussed in detail. Two examples of the entire evolution of the Rossby wave packet are also presented.