Field-aligned electron acceleration in Alfvén waves
Abstract
The field-aligned current of standing Alfvén waves is mainly carried by electrons travelling parallel to the magnetic field. During the upward current phase, magnetospheric electrons travel downward to the ionosphere. In large-amplitude Alfvén waves, where current densities reach a few μAm-2 above the ionosphere, the electrons achieve energies of the order of keV. This problem has been addressed recently in terms of two-fluid theory. The present paper builds on these studies by employing a distribution function formulation. When the electron motion is dominated by the parallel velocity component, we find the B/n curve is central to interpreting the solution: B/n has a peak (i.e., d(B/n)/dℓ = 0, where ℓ is path length along the field line) below which ionospheric electrons are trapped. Above the peak we find the parallel electric field is balanced by the convective plasma acceleration, as suggested by [1999] and has a value of the order of mV/m for ∼1 RE above the B/n peak. The maximum E∥ occurs where d2(B2/n2)/dℓ2 = 0 and is located a couple of density scale heights beyond the B/n peak.
- Publication:
-
Journal of Geophysical Research (Space Physics)
- Pub Date:
- March 2003
- DOI:
- 10.1029/2002JA009551
- Bibcode:
- 2003JGRA..108.1135W
- Keywords:
-
- Ionosphere: Particle acceleration;
- Ionosphere: Auroral ionosphere (2704);
- Ionosphere: Current systems (2708);
- Ionosphere: Ionosphere/magnetosphere interactions (2736);
- electron acceleration;
- Alfvén wave;
- aurora;
- parallel electric field;
- Vlasov equation