Electrostatic noise bands associated with the electron gyrofrequency and plasma frequency in the outer magnetosphere

Naturally occurring noise bands near the electron plasma frequency are frequently detected by the University of Iowa plasma wave experiment on the Imp 6 satellite in the region from just inside the plasmapause to radial distances of about 10 R/subE/ in the outer magnetosphere. The electric field strength of these noise bands is usually small with typical broad band electric field strengths of about 2 μV m-1. A magnetic field has been detected only in a few unusually intense cases, and in these cases the magnetic field energy density is several orders if magnitude smaller than the electric field energy density. The bands are observed at all magnetic latitudes covered by the Imp 6 orbit (vertical-barlambda/subm/vertical-barapproximately-less-than45degree) and appear to be a permanent feature of the outer magnetosphere. They are found at all local times and occur least frequently in the quadrant from 18 to 24 hours. The bands appear to consist of two distinct spectral types which we have called diffuse and narrow band. In both types the center frequency of the noise band is bounded by consecutive harmonics of the electron gyrofrequency, and these noise bands occur most often between harmonics that are near the local electron plasma frequency. They appear to merge continuously into two other types of plasma wave emissions that are found in dissimilar regions of the magnetosphere (upper hybrid resonance noise, also called region 3 noise, inside the plasmasphere and (n+1/2) f/subg/ harmonics in the outer magnetosphere). It is suggested that this smooth merging is caused by changes in the plasma wave dispersion relation that occur as the spacecraft moves from the cold plasma within the plasmasphere into the warm non-Maxwellian plasma found in the outer magnetosphere