Effect of charged dust grains on the electrojet instabilities

Abstract

The Farley-Buneman and Gradient Drift instabilities have been investigated using a 
fluid model, in a partially ionized dusty electrojet region in which dust and 
neutral particles constitute a uniform static background. The effects of 
dissociative electron-ion recombination and dust charge fluctuation on the 
instabilities also have been taken into account. The electron-ion dynamics are 
considered to derive the perturbed densities which further lead to the generalized 
dispersion relation. The dispersion relation describes the propagation of 
electrojet instabilities having frequency within dust ion acoustic range in a 
magnetized partially ionized dusty plasma. The dispersion relation is separately 
solved numerically and analytically for the two values of anisotropy parameters 
which correspond to the two different altitudes in the electrojet region.
It is found that Gradient drift instability is unstable at a much longer 
wavelength as compared to Farley-Buneman instability both with or without
dust. At lower altitudes(90 km) the increase of negative charge on 
dust decreases the threshold electron drift velocity for Farley-Buneman 
instability while it shows the opposite behavior at higher altitudes(100 km). 
A much lower electron drift velocity is required to excite the Gradient drift 
instability than the Farley-Buneman instability at both altitudes. The 
dissociative electron-ion recombination damps both modes much more than the 
dust charge fluctuation. A significant changes in threshold drift velocity is 
observed for the Farley-Buneman mode as compared to the Gradient Drift mode due 
to the two main damping mechanisms. The present analysis is applicable in the 
lower ionospheric electrojet region where meteoric ablation processes are dominant.