Field-aligned currents during IMF~0

We report on field-aligned currents (FACs) obtained from precise magnetic field measurements made onboard the Ørsted and Magsat satellites when the interplanetary magnetic field (IMF) was near zero. We found that Region 1/Region 2 currents persist through southward IMF, IMF~0, and northward IMF; also the central area of both the northern and southern polar caps is always filled with FACs, even during slightly sourthward IMF. A statistical distribution on the latter currents resembles the dayside NBZ system with the downward (upward) currents at dusk (dawn), discovered earlier from Magsat observations. We hypothesize that the quasi-viscous interaction of the solar wind with the magnetospheric lobes may cause a sunward convection of the lobes' field lines through the bunch's core, effectively mapping the FACs of NBZ-type down to the near-pole area.