A Review of Field-Aligned Acceleration by Anomalous Resistivity (a. Precipitating Particles and Auroras) (Proceedings of the Second Symposium on Coordinated Observations of the Ionosphere and Magnetosphere in the Polar Regions: Part I)

Basic concepts of anomalous resistivity and the physical mechanism of current driven instabilities are reviewed with a view to applying them to the field-aligned acceleration of auroral electrons. A paradox that an anomalous 'resistivity' contributes to acceleration of electrons is resolved by taking into account its different effects on electrons in different parts of the distribution function (PAPADOPOULOS: Rev. Geophys. Space Phys, 15, 113, 1977); bulk electrons carrying a field-aligned current are anomalously scattered and decelerated by collisions with turbulent electrostatic waves and contribute to maintain parallel electric field, which in turn accelerates electrons in the tail of the distribution. Among the possible instabilities the electrostatic ion cyclotron instability has the lowest threshold velocity for the wide range of T_e/T_i including T_e/T_i～1, which is valid in the upper ionosphere. The electrostatic ion cyclotron wave is destabilized by a relatively small field-aligned current in the upper ionosphere (KlNDEL and KENNEL: J. Geophys Res., 76, 3055, 1971). A numerical model of the field-aligned acceleration by SATO (Symposium on Plasma Waves in the Magnetosphere, 66,1978) is reviewed in order to emphasize an important role of the ionosphere; the existence of a resistive external circuit (ionosphere) is necessary for resolving the 'chickenegg' cause and effect relationship among parallel electric field, anomalous resistivity and formation of runaway (accelerated) electrons precipitating downward into the ionosphere.

Abstract licence: CC BY

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