Field-aligned currents during IMF 0

Abstract. We report on field-aligned currents (FAC) ob-tained from precise magnetic field measurements made on-board the Orsted and Magsat satellites when the interplan-etary 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 southward IMF. A statis-tical distribution of the latter currents resembles the day-side NBZ system with the downward/upward currents at post-noon/pre-noon hours, discovered earlier from Magsat observations. We hypothesize that the quasi-viscous inter-action 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