CONVECTION OF POLAR-CAP PATCHES OBSERVED AT QAANAAQ, GREENLAND DURINGTHE WINTER OF 1989-1990

During weak B(z) or B(z) < 0 conditions, antisunward convection domina tes the central polar cap as shown by Digisonde drift measurements. Du ring these conditions, polar cap F layer patches are observed routinel y to drift antisunward within the overall plasma convection. A study i s presented which compares patch motion derived from 630.0-nm all-sky intensified camera (ASIC) images taken at Qaanaaq, Greenland (87-degre es CGL) with simultaneously obtained Digisonde drift measurements. Dur ing four periods of the winter 1989/1990 43 630.0-nm patches were iden tified and followed in their motion across the ASIC field of view. The shape, velocity, and drift direction of the individual patches were d etermined. The patch motion was then compared with the Digisonde drift measurements. The drift direction is generally antisunward (+/-25-deg rees); both data sets are in excellent agreement, with a typical +/-20 -degrees scatter around a common central value. The velocity magnitude s from both measurements show considerable variability, but both measu rements generally cover the same velocity range. The variations and va riability of the velocity magnitude are discussed in the context of si multaneous IMF measurements. Rapid changes in velocity were traced to changes in B(z). Deviations from antisunward of the azimuths of the op tical patch drift and the Digisonde drift measurements were controlled by IMF B(y) in agreement with published B(y) control of convection.