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The origins of Birkeland currents
Author(s) -
Stern David P.
Publication year - 1983
Publication title -
reviews of geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 8.087
H-Index - 156
eISSN - 1944-9208
pISSN - 8755-1209
DOI - 10.1029/rg021i001p00125
Subject(s) - physics , magnetopause , geophysics , ionosphere , interplanetary magnetic field , magnetosphere , dynamo , plasma sheet , convection , electric field , polar , noon , interplanetary spaceflight , plasma , field line , boundary layer , computational physics , solar wind , magnetic field , mechanics , atmospheric sciences , astronomy , quantum mechanics
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 of j 11 ∥, 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 B y 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 B z 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.