Electrostatic hydrogen cyclotron waves near one Earth radius altitude in the polar magnetosphere

The wave plasma experiment onboard satellite S3‐3 has detected electrostatic hydrogen cyclotron waves at altitudes near 1R E in the Earth’s polar magnetosphere. The observed wave properties are in excellent agreement with the theoretical dispersion relation as well as the linear instability theory for current driven ion cyclotron waves and are used to determine that the plasma is more than 90% hydrogen, that the electron temperature is about 3.5 electron volts and that T e /T 1 is in the range of 1 or larger. The strongest wave events are associated with large ⩾120mV/m) Dc electric fields described in an earlier paper ( Mozer et al ., 1977) as paired electrostatic shocks. Other wave events, which are not as clearly related to shock structures, usually are imbedded in or specifically correlate with fluxes of electrons from .074 keV to 5.04 keV and turbulent Dc electric fields. These results are consistent with a lower threshold for ion cyclotron waves than for shocks or double layers.