Abstract
Abstract. Hot ion shell distributions could possibly contain enough free energy for waves that could power electron energisation above auroral inverted-V regions. Using both linear theory (WHAMP) and two-dimensional electrostatic simulations, we show that ion shell distributions can cause unstable ion Bernstein mode emissions with high temporal growth rates, as well as perpendicular and parallel e-folding distances, that are in accordance with the tranverse dimensions of auroral arcs and the parallel size of the energisation region, respectively. The phase velocities of the waves are in the proper range to give parallel energisation to electrons with a Landau resonance. The simulation shows that about 90% of the energy goes into electrons and 10% goes into cold ion perpendicular heating. An electron heating rate of ~ 80 eV/s is obtained.Key words. Ionosphere (auroral phenomena) – Space plasma physics (numerical simulation studies; wave-particle interactions)
Highlights
The most widely accepted model for the acceleration of electrons to form the inverted-V spectra above stable auroral arcs is the potential drop acceleration model (Carlqvist and Bostrom, 1970; Evans, 1974)
The maximum possible downward energy flux is vu, where v is the velocity of the ions forming the shell and u is the free energy density of the shell distribution. (This maximum energy flux is not reached in the example given below in Fig. 3 because there the upgoing part still has free energy left, but the point here is to make a rough estimation only.) For example, if u = 0.5 keV cm−3 and v ∼ 1.4 · 106 m s−1, we obtain an energy flux of 13 mW m−2 when projected down to the ionosphere from 5 RE radial distance
We summarise our new findings from our linear and nonlinear calculations concerning shell distributions as free energy sources of Bernstein modes and the associated electron energisation: 1. A hot ion shell distribution contains rather large amounts of free energy and it is a possible candidate for the energy source for waves that would be able to power auroral electron energisation (Fig. 1)
Summary
The most widely accepted model for the acceleration of electrons to form the inverted-V spectra above stable auroral arcs is the potential drop acceleration model (Carlqvist and Bostrom, 1970; Evans, 1974). Lower-hybrid waves (Bingham et al, 1988; Bryant et al, 1991; Bryant and Perry, 1995; Bryant, 1999), as well as Alfven waves (Goertz and Boswell, 1979; Kletzing, 1994; Genot et al, 2000; Stasiewicz et al, 2000), have been suggested for this purpose It has been pointed out by Louarn et al (1994); Volwerk et al (1996); Wygant et al (2000) that Alfven waves contain enough downward Poynting flux to power the aurora in at least some events during disturbed conditions. Particle and wave observations from Polar are used to constrain the model
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
