South Pole Station Ground-Based and Cluster Satellite Measurements of Leaked and Escaping Auroral Kilometric Radiation

Previous work suggests that Auroral Kilometric Radiation (AKR) leaks to low altitudes. To investigate this phenomenon, wideband wave measurements have been conducted simultaneously at South Pole, Antarctica, and at the Cluster satellites, during 35 intervals in 2018-2020. Leaked AKR is observed similar to 5% of the time at South Pole and escaping AKR similar to 31% of the time at Cluster satellites. Both types of AKR are composed of fine structure, and similar fine structure is often observed simultaneously in the AKR at the different locations. Around 0317 UT on 29 June 2020, identical features were observed simultaneously. Cluster interferometry shows that the footprint of the source field line during this event lies within a few hundred kilometers of South Pole. The estimated emitted power of the escaping AKR observed at Cluster in this event exceeds that of the leaked AKR observed at South Pole by many orders of magnitude, suggesting that mode conversion involved in generating leaked AKR is relatively inefficient. AKR fine structure which is identical at the two locations comprises similar to 0.1%-0.3% of AKR observed at Cluster when the South Pole receiver operates, and similar to 2% of AKR observed at South Pole when at least one Cluster satellite is tuned to the appropriate frequency range. The relatively low occurrence rates of coincident fine structure may be attributed partly to geometric and beaming considerations but also suggest that processes involved in generating leaked AKR at levels detectable at ground level have lower probability than those generating escaping AKR at levels detectable by distant spacecraft.