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Auroral radio emissions are of intrinsic interest as part of the Earth’s environment but also provide remote sensing of ionospheric conditions and processes and a laboratory for emission processes applicable to a wide range of space and astrophysical plasmas. At VLF and above, four broad classes of radio emissions occur. All have been observed with ground-based and, in some cases to a lesser degree, with space-based instruments. Related to each type of radio emission, many experimental and theoretical challenges remain, for example: explanations of frequency and time structure, relations to auroral substorms or current systems, and application to remote sensing of the auroral ionosphere. In some cases, basic parameters such as source heights or generation mechanisms are uncertain. Emerging technological advances such as cubesat fleets, ultra-large capacity disk drives, and software defined radio show promise for developing better understanding of auroral radio emissions. 

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.