Ionospheric and Birkeland current distributions for northward interplanetary magnetic field: Inferred polar convection

Abstract

A new, stable system of Birkeland and ionospheric currents has been added to the existing Region 1‐Region 2‐auroral electrojet system when the interplanetary magnetic field (IMF) is directed northward. These currents exist poleward of the Region 1 system, across the polar region, and have been called the northward IMF Bz (NBZ) current system. A companion paper [Iijima et al., this issue] describes in detail the Birkeland currents' magnetic signature, a W‐shaped pattern, in the sunward‐antisunward direction and the NBZ system' dependence on the various components of the IMF. The companion study used MAG‐SAT magnetometer data from 146 orbits over the southern polar regions from November 1979 to January 1980. Data from two days, November 11, 1979, and January 8, 1980, have been analyzed in great detail with regard to the NBZ W signature of Birkeland currents. In addition, a Fourier technique has been used in an analysis of the disturbance component parallel to the main field to derive the ionospheric current system during those two days. The NBZ ionospheric current system has shown a similar W‐shaped pattern with antisunward current (implying sunward convection) over the magnetic pole and with return currents on either side. Multicell patterns emerge from the NBZ ionospheric patterns, and an asymmetry appears to be caused by the IMF By component as well. Suggestions are given for multicell patterns over the polar regions for northward IMF during an IMF By sign change.