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Auroral kilometric radiation (AKR) is bursty electromagnetic emission at about 100 - 500 kHz related to auroral arcs, i.e., dusk and evening side discrete auroras. Because of this, field-aligned potential drops must play some role in AKR 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-frequecy cutoff for the waves. It is composed of both extraordinary and ordinary modes, with the extraordinary mode dominating.
For more information see, e.g., Bahnsen et al. (1989).