High-resolution electron temperature measurements using the plasma line asymmetry

In this paper, we present the first results of a new technique for measuring the electron temperature in the daytime ionosphere using the Arecibo incoherent scatter radar ( ISR). The technique utilizes the plasma line component of the incoherent scatter spectrum. The difference in the up- and down- shifted plasma line frequencies is related to the density and temperature of the ionosphere, as well as more minor effects resulting from photoelectrons, currents, and other sources. The shift is very small ( the order of 1 kHz in a plasma line frequency of several MHz) but can be measured quite accurately with the coded long pulse plasma line technique. We compare the results to ion line measurements of the electron temperature, and the two independent techniques show good agreement. In addition to providing a measure of the electron temperature that is independent of the ion line, the approach allows for a sensitive test of kinetic plasma theory including a magnetic field, gives us the ability to study photoelectron populations and electron currents, and will allow us to constrain ion line fits in the bottomside ( and possibly topside) regions to more accurately fit for composition.