On the Generation of Large Wave Parallel Electric Fields Responsible for Electron Heating in the High-Latitude E Region

Abstract

The sources of parallel electric fields (E_∥) to explain E region electron heating measurements made by incoherent scatter radars have not been resolved. This paper considers the effect of electron density gradients parallel to the geomagnetic field (∇_∥n) on the Farley-Buneman instability and the resulting change in wave δE_∥. The dispersion relation including the ∇_∥n effect is derived and solved for a set of wave vectors at marginal stability. It is shown that ∇_∥n with scales of several kilometers enable propagation of 50 m or longer wavelength waves at large angles (up to 5°) from perpendicularity to the geomagnetic field. The fact that kilometric scales of ∇_∥n were previously shown to occur during strong electrojet and that they coincide statistically well with the altitudes of strongest electron heating support the role of these long-wavelength waves in electron heating. Furthermore, unlike the gradient-drift instability, the ∇_∥n effect contributes to the growth of the waves with the proper k_∥ sign regardless of the direction of the convection electric field E_c; this makes the ∇_∥n effect eligible as a source of electron heating, resulting in the consistent increase of electron temperature with the magnitude of E_c. Moreover, it is shown that the inclusion of the ∇_∥n effect reduces the discrepancy between the theoretically required perpendicular electric field turbulence (to raise the electron temperature to the measured values) and the in situ rocket measurements.