Intense electrostatic waves near the upper hybrid resonance frequency

Plasma wave measurements using instruments on the IMP 6 and Hawkeye 1 satellites are utilized in a study of very intense electrostatic waves near the upper hybrid resonance frequency in the region just outside the plasmapause. These intense plasma wave events have electric field strengths of approx. 1 to 20 mV m-1 and are among the most intense waves seen in the earth's magnetosphere. Detailed studies of more than 140 of these intense electrostatic disturbances reveal that the events occur at all local times and at magnetic latitudes varying from the equator to as high as 500. The polarization of these waves is such that the wave electric field vector is oriented perpendicular to the geomagnetic field. In most cases the center frequency of the intense waves appears to correspond to an (n + 1/2)f/sub g/- harmonic near the upper hybrid resonance frequency. A survey of plasma measurements made simultaneously using the Hawkeye 1 LEPEDEA shows that the occurrence of the intense electrostatic waves is not strongly correlated with the intensities of approx. 1 to 20 keV electrons, but that specific details of the hot electron distribution function are directly related to the wave turbulence. A generation mechanism is proposed which is founded in the theory of electrostatic multicyclotron instabilities. The theory suggests that a nonconvective instability in the (n + 1/2)/sub g/- band including the cold upper hybrid resonance frequency qualitatively reproduces observations of the intensifications near the upper hybrid resonance frequency for a range of plasma parameters. Evidence is presented which suggests the intense electrostatic waves may be a source of non-thermal continuum radiation