Periodic low-frequency electric field structures in a magnetized non-thermal auroral plasma

Abstract

The theoretical explanation of electric field structures associated with density depletion in the Earth's upper ionosphere is presented. Using the quasi-neutrality hypothesis, the effect of excess energetic electron species is studied on the evolution of nonlinear low-frequency ion-cyclotron and ion-acoustic waves in a magnetized auroral plasma. The dynamics of the cold ion beam is governed by the fluid equations and the electron is treated as energetic species with non-thermal density distribution. Numerical computations appear in a series of periodic oscillations, such as spiky, sawtooth and sinusoidal waveforms. The present model can generate up to 18 mV/m electric field amplitude, which is in the range of the FREJA satellite measurements in the auroral acceleration region.

Keywords: Auroral plasma; Computational mathematics; Electric field structures; Geophysics; Low-frequency; Non-thermal electrons; Nonlinear physics; Plasma physics; Quasi-neutrality condition; Wave physics.

Figure 1

The electric field structures observed by FREJA satellite (taken from Kjus et al. [19]).

Figure 2

Geometry of the model.

Figure 3

Normalized electric field structures E(ψ,M) vs ξ for M = 1.25, θ = 2°, δ = 0.2, E₀ = 1.1, α = 0.00 (a), 0.05 (b), 0.1 (c), 0.199 (d).

Figure 4

Normalized electric field E(ψ,M) vs ξ for α = 0.199, θ = 2°, δ = 0.2, E₀ = 1.1, M = 0.22 (a), 1.0 (b), 1.20 (c), 1.25 (d).

Figure 5

Normalized electric field E(ψ,M) vs ξ for α = 0.199, θ = 2°, M = 1.25, E₀ = 1.1, δ = −0.1 (a), 0.0 (b), 0.1 (c), 0.2 (d).

Figure 6

Normalized electric field E(ψ,M) vs ξ for α = 0.199, θ = 2°, δ = 0.2, M = 1.25, E₀ = 0.01 (a), 0.1 (b), 0.8 (c), 1.1 (d).

Figure 7

Normalized electric field E(ψ,M) vs ξ for α = 0.199, M = 1.25, δ = 0.2, E₀ = 1.1, θ = 2° (a), 20° (b), 50° (c), 85° (d).