Continuum radiation and electron plasma oscillations in the distant geomagnetic tail

Abstract

ISEE‐3 electric field measurements are used to examine the properties of electromagnetic continuum radiation in the distant geomagnetic tail. Continuum is observed in all the tail's plasma regions and in the magnetosheath. The power spectrum at 210 RE is nearly identical to that at 40 RE, indicating that the tail cavity forms a reasonably loss‐free waveguide. The angular distribution exhibits both anisotropy, which is similar to that observed nearer the earth, and isotropy for high frequencies (f > 31.6 kHz) in the magnetosheath and for low frequencies (f ≤ 17.8 kHz) in the tail lobes and boundary layer. Isotropic radiation suggests that, in addition to the near earth source, continuum is also generated over a large spatial region in the tail. Electrostatic electron plasma oscillations are also detected in the in the distant tail, and these could represent the local source of the continuum.