Downward transport of electromagnetic radiation by electron holes?

TL;DR

This paper investigates the potential for electron holes to transport electromagnetic radiation from the magnetospheric auroral cavity to lower altitudes, considering various excitation mechanisms and their feasibility.

Contribution

It analyzes the conditions under which electron holes could carry auroral radiation downward, highlighting the improbability of the usual mode but proposing alternative harmonic excitation mechanisms.

Findings

Transport via the X mode is highly improbable for typical conditions.

Higher harmonic excitation could enable radiation transport to lower altitudes.

Electron holes may provide a coupling mechanism between magnetospheric plasma and the atmosphere.

Abstract

An attractive mechanism for radiation transport by electron holes from the magnetospheric auroral cavity source region down to the ionosphere and possibly even down to the atmosphere is examined. Because of the excitation and propagation properties of the X mode, this mechanism turns out to be highly improbable for the usual resonant excitation of radiation of frequency just below the local electron cyclotron frequency, $\omega \lesssim \omega_{ce}$. It could work only, if the auroral ionosphere would be locally perforated being of sufficiently low density for allowing electron holes riding down to low altitudes on the auroral electron beam. If resonant excitation of higher electron cyclotron harmonics, $\omega \sim \ell \omega_{ce}, ~\ell= 2,3,...$, becomes possible, a still unexplored mechanism, then radiation excited inside the hole could be transported to lower altitudes than generated. If this happens, radiation would provide another mechanism of coupling between the magnetospheric plasma and the atmosphere. Keywords: Electron cyclotron maser, electron holes, auroral acceleration, auroral radiation fine structure, auroral kilometric radiation, Jupiter radio emission, Planetary radio emission