Abstract
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.
Highlights
The existence of large field-aligned current densities in narrow auroral structures has been inferred over the last years by using satellites (Cerisier et al, 1987; Berthelier et al, 1988), incoherent scatter radars (Rietveld et al, 1991) and numerical models (Noel et al, 2000). Cerisier et al (1987) interpreted a magnetic pulse recorded by the magnetometer on board the AUREOL 3 low altitude satellite as the signature of current densities as high as 500 μ A/m2 in a current sheet 20 m wide
Very intense but thin sheets or narrow filaments of field-aligned currents (FAC) up to several hundreds of μ A/m2 have been reported by Stauning et al (2003)
Our goal was to investigate the dynamical behavior of the electron under the influence of an applied static electric field
Summary
The existence of large field-aligned current densities in narrow auroral structures has been inferred over the last years by using satellites (Cerisier et al, 1987; Berthelier et al, 1988), incoherent scatter radars (Rietveld et al, 1991) and numerical models (Noel et al, 2000). Cerisier et al (1987) interpreted a magnetic pulse recorded by the magnetometer on board the AUREOL 3 low altitude satellite as the signature of current densities as high as 500 μ A/m2 in a current sheet 20 m wide. The existence of large field-aligned current densities in narrow auroral structures has been inferred over the last years by using satellites (Cerisier et al, 1987; Berthelier et al, 1988), incoherent scatter radars (Rietveld et al, 1991) and numerical models (Noel et al, 2000). Cerisier et al (1987) interpreted a magnetic pulse recorded by the magnetometer on board the AUREOL 3 low altitude satellite as the signature of current densities as high as 500 μ A/m2 in a current sheet 20 m wide. Very intense but thin sheets or narrow filaments of field-aligned currents (FAC) up to several hundreds of μ A/m2 have been reported by Stauning et al (2003). At higher altitudes of 1000 to 4000 km, the downward Birkeland currents are carried by suprathermal electrons at energies from 10 to 500 eV and fluxes greater than 109 electrons.cm−2.s−1 (Klumpar and Heikkila, 1982; Carlson et al, 1998). Klumpar and Heikkila (1982) suggested that they are runaway electrons from the ionosphere produced by a downward field-aligned component of the electric field
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