Digisonde measurements of polar cap convection for northward interplanetary magnetic field

Controversy still exists regarding even the average convection pattern when the interplanetary magnetic field (IMF) has a northward component. Using two years of convection data from a Digisonde located at Qaanaaq only 3° from the corrected geomagnetic pole we have examined the diurnal convection flow direction variation in the central polar cap when the IMF is particularly stable. We find that when Bz is positive, and when By positive and By negative data are treated independently, each exhibits a clear diurnal pattern. The patterns are most nearly consistent with a multicell convection model, e.g. Potemra et al. (1984); there are, however, two anomalies. Our synthesized polar cap convection patterns exhibit a polar cap cell centered on 10 corrected geomagnetic local time (CGLT) when By > 1 nT and 13 CGLT when By < −1 nT in contrast to 06 and 18 CGLT predicted by the multicell models. Furthermore, in contrast to the simple multicell models the convection flow patterns for opposite By polarities are not simple mirror images of each other. When By < −1 nT the convection is directed across the central polar cap toward 02 CGLT for much of the day but when By > 1 nT the flow is tangential to the Qaanaaq geomagnetic latitude for much of the day.