Guided electromagnetic waves observed on a conducting ionospheric tether

Abstract

On the up leg of its flight through the auroral nightside ionosphere to an apogee of 824 km, the tethered double payload Observations of Electric Field Distributions in the Ionospheric Plasma: A Unique Strategy (OEDIPUS) C was the site of experiments on wire‐guided electromagnetic (EM) waves. Waves were transmitted from the upper subpayload to a receiver on the lower subpayload along a conducting wire aligned within a few degrees of the Earth's magnetic field. Such EM waves were observed at almost all frequencies in the range 0.1–8.0 MHz. There was a deep stop band between the cyclotron and upper hybrid resonance frequencies where the cold plasma theory predicts a propagation cutoff, and there were shallower attenuation bands at frequencies where hot‐plasma electrostatic waves may affect the guided EM modes. Resonances of the wire‐guided waves with the tether length were observed throughout the entire tethered portion of the flight. The resonances appear as a set of fringes when all the data are presented in a frequency‐versus‐time summary. The fringe shapes in this summary have been compared with the predictions of an early theory, which give generally good agreement. The exceptions are frequencies close to the stop band, where cold‐plasma dispersion effects are expected to be greatest. Another theory based on a different derivation of the dispersion relation includes a vacuum sheath gap outside the conductor. The absolute fringe intensities and positions predicted agree moderately well with the observations.