Radiometric Measurements of Electron Temperature and Opacity of Ionospheric Perturbations

TL;DR

This study uses broadband radio spectrometry to measure ionospheric perturbations, confirming their spectral signatures and deriving associated electron temperature and opacity changes over diurnal cycles.

Contribution

First direct measurement of ionospheric opacity and electron temperature changes using spectral signatures in the 80-185 MHz range.

Findings

Perturbations increase at sunrise and decline after sunset.

Strongest perturbations show about 1% opacity at 150 MHz.

Typical electron temperature for perturbations is around 800 K.

Abstract

Changes in the sky noise spectrum are used to characterize perturbations in the ionosphere. Observations were made at the same sidereal time on multiple days using a calibrated broadband dipole and radio spectrometer covering 80 to 185 MHz. In this frequency range, an ionospheric opacity perturbation changes both the electron thermal emission from the ionosphere and the absorption of the sky noise background. For the first time, these changes are confirmed to have the expected spectral signature and are used to derive the opacity and electron temperature associated with the perturbations as a function of local time. The observations were acquired at the Murchison Radio-astronomy Observatory in Western Australia from 18 April 2014 to 6 May 2014. They show perturbations that increase at sunrise, continue during the day, and decline after sunset. Magnitudes corresponding to an opacity of about 1 percent at 150 MHz with a typical electron temperature of about 800 K, were measured for the strongest perturbations.