ASPECTS IN COMMON OF HIGH-LATITUDE IONOSPHERIC VORTEX MOTIONS

It is shown that travelling vortices in the ionospheric flow convey momentum in the direction of the phase motion. We use a simple approximate description of flow in the ionosphere based on an analogy with two dimensional incompressible flow. A non-linear calculation is given which shows that although to first order a travelling vortex may carry no net momentum, the net momentum in the direction of travel is proportional to the square of the flow amplitude. The result shows that transport in the ionosphere of both momentum and magnetic flux is independent of the mechanism by which the vortex pattern is generated at high altitude.