Waves in the proton cyclotron frequency range in the CME observed by wind on August 7–8, 1996: theory and data

As first discussed by Farrugia et al. ( J. Geophys. Res., 103, 6543, 1998), coronal mass ejections (CMEs) may support the excitation of electromagnetic ion cyclotron waves (EICWs). The proton plasma beta, and the electron temperature and anisotropy in the front region (∼5 hours, translating to ∼6×10 6 km) of the CME observed by WIND on August 7–8, 1996 favor this possible excitation. Supplementing these measured parameters by other data taken from a survey of CME properties observed by the ISEE 3 spacecraft (Gosling et al., J. Geophys. Res., 92, 8519, 1987), we solve the EICW dispersion relation numerically. We find short e-folding times of EICWs, of the order of 5 min, i.e., much less than the typical evolution time of these ejecta. We suggest that high resolution data will show enhanced power in the 0.5 Hz range.