Auroral kilometric radiation (AKR) is bursty electromagnetic emission at about 100 - 500 kHz related to auroral arcs. Because of this connection to discrete aurora, field-aligned potential drops must play some role in their production. The source region altitude is about 3000 - 20000 km; however, at a given time only a small altitude range is operational.
The radiation is believed to be generated at frequencies near the local electron cyclotron frequency fce, which often acts as low-frequency cutoff for the waves. It is composed of both extraordinary and ordinary modes, with the extraordinary mode dominating (see Waves in cold plasma).
For more information see, e.g., Bahnsen et al. (1989).