Abstract
A qualitative explanation is proposed for the main features of quiet‐time Birkeland currents. The major conclusions are as follows: (1) The source of region 1 currents is the interplanetary electric field, linked to the polar ionosphere directly along open field lines near noon but indirectly, via the plasma sheet, at most other longitudes. (2) Region 2 arises from convective charge separation, owing to guiding center drifts. On the dayside, secondary charge separation may occur, extending the current pattern sunward. (3) The magnetopause boundary layer flow is not a major energy source ofj11∥, and neither are dynamo processes in convected plasmas or in the plasma sheet. (4) The convection reversal is expected to occur (as observed) in the interior of region 1, often near its poleward edge. (5) The cusp currents are associated with an inhomogeneity of the polar electric field, correlated with interplanetary By and first observed by Heppner, though contributions by the boundary layer are not ruled out. (6) The four‐lobed polar electric field patterns occasionally observed during times of northward interplanetary Bz are generated by a boundary layer dynamo and signify the temporary existence of a closed magnetospheric configuration. (7) The branching ratio between two routes by which magnetospheric space charge may be neutralized, via the ionosphere and via polarization currents, is estimated, with and without considerations of particle mirroring.
Published Version
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