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Instruments on the Auroral Turbulence rocket detected several intervals of weak electromagnetic oscillations at frequencies of 6-13 Hz in a strongly flickering auroral arc. These oscillations have amplitudes of up to dB ~ 3 nT and dE ~ 4 mV/m and have downward field-aligned Poynting fluxes of up to ~ 10-5 W/m2. Fluctuations in the parallel electron flux at about 9 Hz were observed in association with the strongest of these oscillations. Simultaneous ground-based optical data show that the arc was flickering at frequencies of 8-15 Hz. The observed frequencies would match the oxygen cyclotron frequency at ~ 4500 km altitude. In one wave/particle event the apparent lag of the waves behind the modulated electrons implies a modulation source altitude of 2500-5000 km. We interpret these waves as electromagnetic ion cyclotron waves originating in the auroral acceleration region.
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