Impact of electron thermal effects on Farley‐Buneman waves at arbitrary aspect angles

Abstract

Using a standard 8‐moment expansion of the fluid equations, we have extended fluid calculations of the effect of electron temperature feedback on the linear Farley‐Buneman instability theory to include the contribution of field‐aligned heat flow and field‐aligned wave electric fields through nonzero‐aspect angles. Our treatment includes arbitrary ion magnetization and neutral winds but is limited, for simplicity, to zero flow angles. Our results indicate that, for 3‐m waves, electron thermal corrections are significant (threshold phase velocities greater than predicted by isothermal theory by 20% or more) at aspect angles less than 0.35° for altitudes less than 103 km. Similar but smaller numbers are obtained for 10‐m waves. The impact of the thermal corrections normally also decreases rapidly with increasing altitude. These results provide a straightforward explanation for equatorial observations of 3‐m phase velocities that are at least 30% greater than the isothermal ion‐acoustic speed below 105 km in the equatorial regions. The altitude dependence of the observed phase speeds also mimics very well the behavior seen in our calculations. The implication is that the aspect angles of the structures must be smaller than 0.3°. This is consistent with recent findings from radar interferometry.