The influence of electron density gradient direction on gradient-drift instabilities in the E-layer of the ionosphere

TL;DR

This paper investigates how the direction of electron density gradients affects gradient-drift and Farley-Buneman instabilities in the ionosphere's E-layer, revealing significant effects when gradients align with magnetic fields or wave vectors.

Contribution

It introduces additional terms into the dispersion relation for ionospheric instabilities, accounting for divergence of particle velocity and electron density gradients along magnetic fields, which were previously neglected.

Findings

Additional terms significantly affect instability growth rates when gradients align with magnetic fields.

Different instability conditions are identified for equatorial and high-latitude regions.

Results align with existing experimental data.

Abstract

We show that the dispersion relation for gradient-drift and Farley-Buneman instabilities within the approximation of the two-fluid MHD should contain the terms which are traditionally supposed to be small. These terms are caused by taking into account divergence of particles velocity and electron density gradient along the magnetic field direction. It is shown that at heights below 115km the solution of the dispersion relation transforms into standard one, except the situations, when the electron density gradient is parallel to magnetic field or wave-vector. In these cases the traditionally neglected summands to the growth rate of the irregularities becomes significant. The additional terms depend on relative directions of electron density gradient, magnetic field and mean velocities. This leads to the different instability growth conditions at equatorial and high-latitude regions of the ionosphere. The obtained results do not contradict with the experimental data.