OBSERVATION OF ELECTROMAGNETIC OXYGEN CYCLOTRON WAVES IN A FLICKERING AURORA

Instruments on the Auroral Turbulence rocket detected several intervals of weak electromagnetic oscillations at frequencies of 6-13 He in a strongly flickering auroral are. These oscillations have amplitudes of up to delta B similar to 3 nT and delta E similar to 4 mV/m and have downward field-aligned Poynting fluxes of up to similar to 10(-5) W/m(2). Fluctuations in the parallel electron flux at about 9 Hz were observed in association with the strongest of these oscillations. Simultaneous groundbased optical data show that the are was flickering at frequencies of 8-15 He. The observed frequencies would match the oxygen-cyclotron frequency at similar to 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.