RESPONSE OF THE POLAR-CAP F-REGION CONVECTION DIRECTION TO CHANGES IN THE INTERPLANETARY MAGNETIC-FIELD - DIGISONDE MEASUREMENTS IN NORTHERN GREENLAND

Results of ionospheric drift measurements with a Digisonde 256 digital ionospheric sounder located at Qaanaaq, Greenland (87-degrees-N, corrected geomagnetic latitude), are presented. Digisonde drift data have been related to the interplanetary magnetic field (IMF) measured by the IMP 8 satellite for 32 days during 1986, 1987, and 1988. Extremely good statistical agreement between these measurements and convection directions derived from satellite instrumentation id demonstrated when the IMF z component is negative. For B(z) negative and B(y) negative the daily average convection direction is centered on -12-degrees (anticlockwise) from the antisunward direction. When B(z) is negative but B(y) is positive, the convection direction is centered on +36-degrees. These directions differ by 3-degrees and 9-degrees, respectively, from the models of Heppner and Maynard (1987). The variation about these values is approximately +/- 20-degrees. The excellent agreement between the Digisonde measurements and models derived form satellite measurements demonstrates the utility of the Digisonde for making ground-based measurements of the convection direction in the polar cap F region when B(z) is south. The convection directions under conditions of positive B(z) have also been examined, and we have measured three types of temporal variation in azimuth, namely, an ordered and slowly (OS) varying change in direction, an ordered and quickly (OQ) varying change in direction, and disordered (D) variations in direction. The later are believed to result from a breakdown of the analysis technique due to velocity shears in the vicinity of polar cap arcs, and we estimate that they account for approximately 25% of the measurements when B(z) > 0. When B(z) is positive and B(y) is negative, our small subset of OS measurements supports the distorted two-cell model of Heppner and Maynard (1987). The remainder of the measurements show no well-defined daily average convection direction or diurnal variation. Likewise for B(z) positive and B(y) positive, no well-defined convection direction can be discerned, nor can any diurnal variation. The existence of OQ variations when B(z) > 0 suggests that meaningful average statistical convection patterns may be much harder to synthesize than similar patterns when B(z) < 0.