Thermal effects on Farley–Buneman waves at nonzero aspect and flow angles. I. Dispersion relation

Abstract

With the increasingly accepted notion that E-region electrostatic plasma waves move at their instability threshold speed when they attain their maximum amplitude, it has become more important to determine just what that threshold speed is supposed to be. An accurate determination requires a calculation of the electron temperature fluctuation level, which can sometimes dramatically influence the results. In this paper, the Grad 8-moment transport equations have been employed with the addition of a generalized electron cooling rate to account for cooling via inelastic collisions, and a general electron volume heating rate that includes frictional heating as a special case. The derived generalized dispersion relation is presented in such a way that a variety of other earlier treatments, including the isothermal and adiabatic limits and an instability associated with electron friction, all fall out transparently, allowing us to easily compare our results with earlier ones while tracking down the physical processes involved. The presentation format is also geared to facilitate the computation of the dispersion relation for the purpose of comparing the theoretical results with observations.

Unexpected rapid decrease in phase velocity of submeter Farley‐Buneman waves with altitude

“…We have analyzed the results of experimental studies of Farley‐Buneman waves over Jicamarca by probing the equatorial electrojet at Bragg's scales 3 and 0.35 m. We have shown that the advanced linear theory [ Kagan and St.‐Maurice , 2004; Kissack et al , 2008a, 2008b] explains well the altitude dependence of V ph for JULIA vertical, 23‐ and 51‐degree west transmissions, and observations of AMISR‐P at 0 and 20 degrees west. The remarkable match of the linear theory predictions to observations seems to further confirm the long suspected fact that whatever the nonlinear process generating FB waves is, it produces waves moving at their linear threshold speed.…”

Fluctuations in the direction of propagation of intermittent low‐frequency ionospheric waves

“…Measurements of aspect sensitivity of Farley‐Buneman waves by Jackel et al [1997, 2002] with a coherent scatter radar showed that the FB aspect angle observed in the equatorial electrojet (as opposed to auroral region) was confined within less than ∼3° off the ‐perpendicular direction. The FB theory that included electron thermal corrections by Kagan and St. ‐ Maurice [2004] and Kissack et al [2008a, 2008b] predicted the Farley‐Buneman aspect sensitivity to be within ∼2.5°. Using the large Jicamarca radar and advanced analysis techniques, Kudeki and Farley [1989] demonstrated that the aspect angle of the FB waves deviated by angles between 0.1° and 0.4°.…”

The equatorial E-region and its plasma instabilities: a tutorial

“…More recently Kissack et al (2008a) and Kissack et al (2008b) have written papers discussing in great detail thermal effects and their relation to aspect angles and flow angles. The problem with this is that it is dangerous to assume large flow angles, in particular, since, as we have seen, large scale velocities and electric fields are likely to be quite turbulent, at least at the equator, and radars will always respond most strongly to the regions where the flow angle is small.…”