On the generation of auroral electromagnetic ion cyclotron ELF waves

Freja observations of electromagnetic emissions around half of the local proton gyrofrequency are investigated. By reconstructing the wave distribution function we obtain an estimate of the distribution of energy in wave vector space. This distribution is compared in detail with the spectrum of unstable wave vectors predicted by linear stability analysis including precipitating auroral electrons as a source of free energy. We find good agreement between the unstable range of wave vectors and the wave vectors dominating the reconstructed wave distribution function. The agreement leads to a consistent picture of the generation of auroral electromagnetic ion cyclotron ELF waves. 11 refs