An Alfven Wave Model of Auroral Arcs
The association of auroral arcs and (upward directed) parallel electric fields above the ionosphere can be regarded as a well established fact. Equally well established is the association of both with intense field-aligned currents. The theoretical literature on the formation of auroral arcs has therefore focussed on the origin of the parallel electric fields and the elementary processes maintaining them. Since the early work of Kindel and Kennel (1971) the latter have been preferentially attributed to current-driven instabilities. A wide variety of mechanisms have been investigated among which electrostatic double layers, anomalous resistivity, the magnetic mirror force (loss cone restriction of upward j11) and kinetic Alfvén waves are the most popular ones (see reviews by Shawhan et al. (1978) and Kan (1982)). The overwhelming majority of the theories deal with this subject in the electrostatic approximation, i.e. the currents are regarded as strictly field-aligned and the magnetic effects on the plasma dynamics are neglected. Even the observed encounters of large spatially confined transverse electric fields at several 1000 km altitudes by the S 3-3 satellite have been named electrostatic shocks (Mozer et al., 1977), although there is neither clear evidence for their electrostatic (k x E = O), nor for their shock, nature (Kan, 1980).
KeywordsCurrent Sheet Plasma Sheet Acceleration Region Alfven Wave Transverse Electric Field
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