Relationship of the polar cap current system to the north-south component of the interplanetary magnetic field

The daily magnetic variation at a polar cap station, Resolute Bay, is examined for its dependence on the north-south component B/sub z/ of the interplanetary magnetic field (IMF). The magnetic perturbations are seen to be in approximately the same direction in the nightside polar cap for both northward and southward IMF, the amplitudes of the perturbations being larger for southward IMF. In the dayside perturbations, significant differences between the northward and southward IMF cases are observed. Examination of Thule perturbations shows the same serious discrepancy near noon. The observations are consistent with antisunward current (and sunward convection) in a central strip of the polar cap, as was first suggested by Maezawa (1976). Our tentative interpretation for the overall pattern of the polar ionospheric currents during northward IMF differs substantially from that of Maezawa, however. It is suggested that the overall pattern consists of two of the standard two-cell current patterns placed in juxtaposition such that the interface between them is the site of the antisunward current (sunward convection). Within the centers of each of these two patterns the currents are sunward