On the formation of auroral arcs and acceleration of auroral electrons

Abstract

It is suggested that the highly structured auroral arc is caused by a current‐driven laminar electrostatic shock oblique to the geomagnetic field. Electrons are accelerated by the potential jump associated with the shock. The shock is assumed to be confined to a plane. Self‐consistent solutions to the Poisson‐Vlasov systems are calculated for the electrostatic potential. Adiabatic theory is used to calculate the ion number density in terms of the electrostatic potential and its derivatives. The electrons are assumed to be highly magnetized so they can only move parallel to the magnetic field. Solutions are exhibited for two plasma models: (1) streaming electrons and a two‐temperature distribution of ions and (2) streaming electrons and ions and thermal electrons and ions. In the latter model, solutions can be obtained for an arbitrary potential jump across the shock. The shock is identified with the linear electrostatic ion cyclotron wave, and stability of these waves is examined to determine conditions for the formation of oblique shocks. Finally, the theory is discussed in the context of the magnetosphere, and possible model shocks are exhibited and discussed in terms of auroral arc formation.

Small‐scale, dispersive field line resonances in the hot magnetospheric plasma

“…This feature of dispersive Alfvdn waves suggests that they may be responsible for some classes of auroral arcs, produced by sheet-like fluxes of precipitating electrons with energies from 100 eV up to tens of keV [Swift, 1975;Davis, 1978 Owing to the intrinsic inhomogeneity of the magnetospheric plasma and geomagnetic field, two types of dispersion can affect small-scale Alfv•n waves that propagate between the equatorial magnetosphere and ionosphere. In the relatively cold, low-altitude plasma, where the Alfv•n speed is much larger than the electron thermal speed, the dispersion is due to the finite electron inertia (inertial dispersion) [Goertz and Boswell, 1979;Lysak and Carlson, 1981].…”

Particle simulation of the auroral zone showing parallel electric fields, waves, and plasma acceleration

“…The argument for the particle driver is that energy and pitch angle anisotropies in the magnetotail distribution functions lead to the mirroring of ions and electrons at different altitudes, which creates a charge separation and a parallel electric field [Alfvdn and Fiilthammar, 1963;Persson, 1963]. Many models of the steady state auroral electrostatic potential and the current-voltage relationship are based on this premise [Knight, 1973;Lemaire and Scherer, 1974;Swift, 1975;Kan, 1975 Cornwall, 1990]. Other approaches assume that finite electron inertia causes a parallel electric field to develop when magnetospherically generated kinetic Alfv6n waves reflect off the ionosphere.…”

A review of electrostatic wave measurements on auroral magnetic field lines.

“…Common detection by S3-3 (MOZER et al, 1977) indicates considerable extent along B, however. Other models invoking larger oblique shock structures (KAN, 1975;SWIFT et al, 1976;SWIFT, 1975) have also been recently proposed and it seems likely that considerably more theoretical effort will be expended in the near future. Even earlier, KINDEL and KENNEL (1971) predicted that plasma in the altitude range of one Earth radius should first go unstable to electrostatic ion cyclotron waves.…”