THE IONOSPHERIC PLASMA-FLOW AND CURRENT PATTERNS OF TRAVELING CONVECTION VORTICES - A CASE-STUDY

Following a short duration density enhancement in the solar wind, obse rved by the AMPTE/IRM spacecraft, transient disturbances appeared in t he polar ionosphere in the prenoon local time sector which were identi fied as Travelling Convection Vortices (TCV). This event has been stud ied intensively by combining radar and magnetometer observations. EISC AT radar was operated in the special programme U.K.-POLAR which provid es F-region plasma parameters from invariant latitudes around 72-degre es at a rate of one sample per 15 s. The combined data set provides a detailed picture of the drift pattern of the plasma and the three-dime nsional current distribution. There are two Hall current eddies drifti ng westward at a speed of 0.15-degrees s-1. The leading one circulatin g clockwise is associated with a downward field-aligned current and th e oppositely circulating eddy with an upward current. The ionospheric conductivity seems to be enhanced in the leading vortex compared to th e trailing, although the latter is connected to an upward field-aligne d current. Still unexplained is the mechanism generating the electric field which drives the vortices. The direction of the electric field o bserved in the ionosphere is opposite to that expected if the source w ere a compression of the magnetosphere.