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Abstract 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 ∼5% of the time at South Pole and escaping AKR ∼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 ∼0.1%–0.3% of AKR observed at Cluster when the South Pole receiver operates, and ∼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.
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Statistical Characteristics of Leaked AKR Observed at South Pole Station, Antarctica
There is mounting evidence of a component of terrestrial auroral kilometric radiation (AKR) that is converted to whistler mode and radiated downward toward the planet, observable even at ground level. Three years of data from South Pole Station in 2018-2020 provide statistics of characteristics of leaked AKR at ground level. The events occur in an approximately 90--day interval around winter solstice, apparently requiring darkness in the ionosphere to be observed at ground level. They favor pre--midnight/midnight magnetic local times, which is consistent with the connection of AKR, observed in space, to auroral substorms. The frequency distribution of ground{level AKR is truncated compared to that observed in space, with primarily the higher end of the frequency range being observed, 400--600 kHz, corresponding to the low altitude range of source heights, 2500-3500 km, assuming generation at the electron cyclotron frequency. Approximately half of the events have maximum radiance exceeding 1.5×10^18 W/m2/Hz, with the strongest events exceeding 10^16 W/m2/Hz; these intensities are up to two orders of magnitude lower than those observed in the ionosphere, suggesting that most of the leaked AKR is at large wave normal angles that cannot penetrate the Earth{ionosphere boundary.
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- Award ID(s):
- 2205753
- PAR ID:
- 10616902
- Editor(s):
- Fischer, G; Jackman, C M; Louis, C K; Sulaiman, A H; Zucca, P
- Publisher / Repository:
- Trinity College Dublin
- Date Published:
- Subject(s) / Keyword(s):
- Planetary Radio Emissions Auroral Kilometric Radiation
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.25546/103087
