The relationship of field‐aligned currents to electrostatic ion cyclotron waves

Two sources of free energy for driving ion cyclotron waves have been observed on the S3‐3 satellite: field‐aligned currents and ion beams. Since the waves are destabilized by the thermal electron drift and not the current, before correlating observations of field‐aligned currents with ion cyclotron waves, it is first necessary to determine that the current is primarily carried by thermal electrons. Comparisons of the current carried by energetic particles with the current measured by the magnetometer during several events shows that this is sometimes the case. Statistical studies indicate that the field‐aligned current density is correlated with the spectral density during ion cyclotron events. The combination of the results of this report and those of Kintner et al. (1979) is consistent with the hypothesis that the observed ion cyclotron waves are driven by a combination of ion beams and electron drift. However, the available data set does not unambiguously identify the free energy source.