Interpreting the Doppler spectrum of coherent scatter from topside equatorial spread F

Abstract

A theory predicting the shape of coherent scatter radar Doppler spectra from field aligned plasma irregularities is presented. The theory pertains to electrostatic turbulence in guiding center plasmas and utilizes a test particle approach. Numerous simplifying assumptions are made which limit the applicability of the theory. We find that the theory may hold for the case of topside equatorial spread F irregularities in the so-called inertial regime. Here, the Doppler spectra are predicted to be essentially Gaussian in shape with a width equal to the RMS velocity of the plasma in the scattering volume. The theory is tested against the output of a direct numerical simulation of the inertial interchange instability and against new data from Jicamarca taken with an aperiodic pulsing technique. An experimental means of inferring the wave number spectrum of ionospheric irregularities using ground-based radar is outlined.