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

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 ∼100 kHz and occurrence in quasi-periodic bursts lasting < 1 s when passing at full Alfvén 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.

Properties of AKR‐Like Emissions Recorded by the Low Altitude Satellite DEMETER During 6.5 Years

“…This was confirmed with many other events by LaBelle et al (2015). They show that the occurrence Several processes have been proposed to explain these observations (Krasovskiy et al, 1983;LaBelle & Anderson, 2011;LaBelle et al, 2015;Oya et al, 1985;Treumann et al, 2018). It is expected that the penetration of AKR to low altitudes must be related to CMI which can excite Z-mode emissions in regions close to X-mode emissions (Mutel et al, 2011).…”