Electron thermal effects on the Farley–Buneman fluid dispersion relation

Abstract

The traditional linear fluid dispersion relation of Farley–Buneman waves has been generalized by including, for the electron gas, the effects of collisional energy exchange, as well as thermal force and thermoelectric effects associated with heat flow. The formalism used is that of Schunk [Rev. Geophys. Space Phys. 15, 429 (1977)] for Grad’s 8-moment approximation, to which inelastic energy exchange has been added phenomenologically. The resulting dispersion relation recovers both the traditional isothermal and adiabatic limits, as well as the dispersion relation of Pécseli et al. [J. Geophys. Res. 94, 5337 (1989)] as a special case. Owing to the fact that the electron–neutral interaction is far from being of the Maxwell molecule type, it is found that, contrary to suggestions in the literature, adiabaticity does not hold at the larger wavelengths of the instability. In the small wave-number limit, the linear instability threshold speed of the waves takes the form [(γeTe0+Ti0)/mi]1/2, with the effective γe being a sensitive function of aspect angle. Its value can be as small as 0.28 or as large as 3.4 depending on conditions.

Ion thermal effects on E-region instabilities: 2D kinetic simulations

“…where m i;e are the reduced ion and electron masses, m i;e ¼ m i;e m n = m i;e þ m n À Á ; d i;e is the average fraction of energy lost by the ion or electron during one collision, d i;e ¼ 2m i;e =ðm i;e þ m n Þ; m n is the average mass of the neutral species; n i and n e are the ion-neutral and electron-neutral collision rates; T i;e;n are the ion, electron and neutral temperatures in energy units; V i;e gives the average drift speed of the ion or electron population; and Q i;e includes other terms such as heat conductance and diffusion which become important at short wavelengths (Kissack et al, 1995). When the R.H.S of this equation is small, as is usually the case for electrons in the upper E-region and short wavelength modes, then this equation predicts adiabatic behavior.…”

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

“…Under these conditions, the observed phase speeds were clearly faster than the isothermal ion-acoustic speed, and compared more favorably with a speed associated with adiabatic electrons. [12][13][14][15][16][17][18][19][20][21][22][23][24] We note that argued that there seemed to be little need to consider ion thermal corrections below 110 km altitude. This was contrary to expectations from the isothermal ionacoustic speed, but proved to be in excellent agreement with nonisothermal calculations under small aspect and flow angle conditions.…”

The effect of electron‐neutral energy exchange on the fluid Farley‐Buneman instability threshold

“…As we mentioned in the introduction, this paper uses Kissack et al's [1995] approach as its cornerstone. Thus we employ fluid moment equations for the electrons (continuity, momentum, thermal energy, and heat flow) based on Grad's 8-moment method, with inelastic energy effects added phenomenologically, using welldocumented expressions from the published literature.…”