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Ann. Geophys., 24, 2391-2401, 2006
www.ann-geophys.net/24/2391/2006/
© European Geosciences Union 2006
A kinetic model for runaway electrons in the ionosphere
G. Garcia1,3 and F. Forme1,2
1Centre d'Études des environnements Terrestre et Planétaires, 78140 Vélizy, France
2Université de Versailles Saint-Quentin en Yvelines, Versailles, France
3Université de Pierre et Marie Curie, Paris VI, France
Abstract. Electrodynamic models and measurements with satellites and
incoherent scatter radars predict large field aligned current
densities on one side of the auroral arcs. Different authors and
different kinds of studies (experimental or modeling) agree that
the current density can reach up to hundreds of µA/m2.
This large current density could be the cause of many phenomena
such as tall red rays or triggering of unstable ion acoustic
waves. In the present paper, we consider the issue of electrons
moving through an ionospheric gas of positive ions and neutrals
under the influence of a static electric field. We develop a
kinetic model of collisions including electrons/electrons,
electrons/ions and electrons/neutrals collisions. We use a
Fokker-Planck approach to describe binary collisions between
charged particles with a long-range interaction. We present the
essential elements of this collision operator: the Langevin
equation for electrons/ions and electrons/electrons collisions and
the Monte-Carlo and null collision methods for electrons/neutrals
collisions. A computational example is given illustrating the
approach to equilibrium and the impact of the different terms
(electrons/electrons and electrons/ions collisions on the one hand and
electrons/neutrals collisions on the other hand). Then, a parallel
electric field is applied in a new sample run. In this run, the
electrons move in the z direction parallel to the electric field.
The first results show that all the electron distribution
functions are non-Maxwellian. Furthermore, runaway electrons can
carry a significant part of the total current density, up to 20%
of the total current density.
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