Sub-ionospheric AKR: A possible mechanism for its transport down from the topside generation region to the F layer and ground

TL;DR

This paper proposes that electron exhausts generated in collisionless reconnection could transport auroral kilometric radiation from the topside to ground level, offering new insights into reconnection physics and auroral phenomena.

Contribution

It introduces a novel mechanism for low-altitude AKR transport via electron exhausts, supported by theoretical modeling and analysis of observational data.

Findings

Electron exhausts can generate X-mode AKR via ECMI.

Transport of AKR down magnetic flux tubes is theoretically possible.

Observational evidence is limited but suggestive of this mechanism.

Abstract

Recent theoretical work shows that "electron exhausts", elongated regions of depleted electron density shown by PIC codes to be generated in collisionless reconnection, can in principle become sources of X-mode Auroral Kilometric Radiation generated by the electron cyclotron maser instability (ECMI). In this paper it is suggested that under certain conditions such X-mode AKR can possibly be transported down along the auroral magnetic flux tubes to low altitudes, in extreme cases even penetrating below the ionospheric F- and E-regions to reach ground level. The characteristic features of low-altitude AKR produced and transported by this mechanism would be bandwidths of order $\sim$100 kHz and occurrence in quasi-periodic bursts lasting $< 1$ s when passing at full Alfv\'en speed, $>1$ s when retarded. Most published observations of low-altitude AKR have insufficient time resolution to detect these features, although a few are suggestive of them. The few observations with marginally sufficient time resolution are so far neither consistent nor inconsistent with these predictions, suggesting that occasions when electron exhausts transport AKR all the way to low altitudes may be rare. However, vigorous experimental effort to test these theoretical predictions is warranted because of its physical and astrophysical significance. They would also provide an additional method to remotely detect and investigate reconnection physics.