VORTICITY AND DIVERGENCE IN THE HIGH - LATiTUDE UPPER THERMOSPHERE

Measurements made from the Dynamics Explorer-2 satellite in November 1981 through January 1982 and November 1982 through January 1983 have been analyzed to determine the divergence and vertical component of vorticity of the high-latitude n utral wind field in the upper thermosphere for quiet (Kp <3) and active (3+ < Kp <6) geomagnetic conditions and for both northern (winter) and southern (summer) hemispheres. This analysis provides the first experimental determination of the large-scale vorticity and divergence patterns in the polar thermosphere and provides insight into the relative strengths of the different sources of momentum and energy responsible for driving the winds. The principal findings from this work include the following: The mean neutral wind pattern isdominated by rotational f ow rather than by divergent flow, with a typical vorticity: divergence ratio of-2:1 for active conditions and -4:1 for quiet conditions. Comparison of the divergence and vorticity patterns for quiet and active conditions indicates that the divergent component of the neutral flow intensifies more significantly with increasing eomagnetic activity than does the rotational component.