STATISTICS OF THE LOWER-HYBRID WAVE CAVITIES DETECTED BY THE FREJA SATELLITE

Localized electrostatic wave packets in the frequency region of lower hybrid waves have been detected by the instruments on the FREJA satell ite and also earlier by instrumented rocket payloads. These waves are often associated with local density depletions, indicating that the st ructures can be interpreted as wave-filled cavities which are strongly elongated along the magnetic field. The basic features of the observa tions are discussed, providing a survey of the conditions for occurren ce and spatial distributions. The basic properties of the individual c avities and associated fluctuating electric fields are discussed as we ll, and typical densities, widths, and other characteristics are obtai ned for selected orbits.