Extreme ionospheric effects in the presence of high electric fields

Abstract

In the presence of high-convection electric fields, theoretical con-siderations and computer models predict, among other effects, large increases in the ion temperature, the molecular ions and horizontal neutral winds in the high-latitude F region, but experi-mental evidence of these effects has been difficult to obtain. Here we report on measurements of very high perpendicular convection velocities of ∼3.8 km s⁻¹, corresponding to electric fields of 190 mVm⁻¹, that were made in the auroral F region of the ionos-phere with the tristatic incoherent scatter radar at EISCAT in northern Scandinavia under magnetically perturbed conditions. These high velocities were associated with very high ion tem-peratures of 12,000 K without being accompanied by commensurate changes in the electron temperature. The large increase of the ion temperature can be accounted for quantitatively by Joule heating. The constraint of energy conservation during this event implies a substantial increase of molecular ions in the F layer, attaining values of more than 70% at 250 km altitude. Similarly, momentum conservation allows us to estimate neutral winds of up to 600 m s⁻¹ mainly in the zonal direction.