Steepened magnetosonic waves in the high β plasma surrounding Comet Giacobini-Zinner

We extend the previous studies of intense hydromagnetic waves at Giacobini-Zinner to investigate the mode and direction of wave propagation. Simultaneous high-resolution measurements of electron density fluctuations demonstrate that the long period (∼100 s) waves are propagating in the magnetosonic mode. Principal axis analyses of the long period waves and accompanying partial rotations show that the sum of the wave phase rotations is 3600C, indicating that both are parts of the same wave oscillation. From the time sequence of the steepened waveforms observed by ICE, we demonstrate that the waves must propagate towards the sun with C/sub ph/ < V/sub sw/. All available observations are consistent with wave generation by the resonant ion ring or ion beam instability which predicts right-hand polarized waves propagating in the ion beam (solar) direction. The large amplitudes Δ polarized B/absolute value of B∼0(1) and small scale sizes (rotational discontinuities) of the cometary waves suggest that rapid pitch-angle scattering and energy transfer with energetic ions should occur. Since the waves are highly compressive, Δ absolute value of B/absolute value of B = 0(0.5), one can also anticipate first-order Fermi acceleration. 15 refs., 6 figs