Extent of thermal non-equilibrium in the ionosphere

Abstract

The extent of thermal non-equilibrium in the ionosphere, during sunspot minimum, is examined using electron temperatures derived from ionosonde-backscatter comparisons and backscatter spectra. The ionosonde-backscatter comparisons are used to provide information below the F-layer peak, a region where no systematic results are available. The backscatter spectra are used to obtain electron temperatures above the F-layer peak (nominally 250 km) to heights of about 500 km. The studies indicate that the electron temperatures increase with height from 120 to 200 km and 300 to 500 km. In the interval from 200 to 300 km, the temperatures increase or decrease depending upon the electron density at these levels. The electron temperatures and their height gradients show a wide variation from one day to another, but are found to be closely related to the electron density variations. As such, any comparisons of electron temperatures obtained by different techniques, at the same or different locations, may not be conclusive if electron densities are not the same at these locations during the time of comparisons.