Plasma Waves Observed Inside Plasma Bubbles in the Equatorial F Region

摘要

Plasma waves have been detected within and around density depletions in thetopside equatorial F region by the electric and magnetic field sensors of the Extremely Low Frequency Wave Analyzer (ELFWA) instrument which is part of the Low Altitude Satellite Studies of Ionospheric Irregularities experiment on the Combined Release and Radiation Effects Satellite. The plasma waves include both electrostatic waves that have a small magnetic field component and electromagnetic waves propagating in the extraordinary mode. Thus they are not simply zero frequency irregularities as generally assumed by previous investigators who were working without the benefit of high sensitivity AC magnetic field measurements. The waves exhibit no resonances or cutoffs at characteristic frequencies of the plasma within the range of the ELFWA which is 2-125 Hz. They occur from late evening to early morning primarily at altitudes around 400-500 km. An example has been observed as high as 1500 km. The waves are associated with plasma depletions from a factor of 2 to a factor of 80 less than the surrounding density. The observations indicate that the waves are related to equatorial spread F.