A correlated study of ELF waves and electron precipitation on Ogo 6

Abstract

The Ogo 6 ELF chorus records from the search coil magnetometer have been compared with simultaneous electron precipitation records. The chorus signals observed in the vicinity of field lines passing through the outer magnetosphere were characteristically accompanied by electron precipitation in the same region. Both the chorus and the precipitation records consisted of a series of sharp peaks. Although in some cases chorus and precipitation peaks appeared to be associated, the observed peaks did not in general coincide. Comparison of the chorus measurements on Ogo 6 and Ogo 5 suggests a model in which the chorus is ducted along field lines to within less than 1 RE above the Ogo 6 orbit after which it diverges from the field lines and is deflected toward the local vertical. The result is equatorward skewing of the average wave pattern with respect to the precipitation pattern. Some of the emerging waves with an initial equatorward component pf velocity may suffer reflection at the plasmapause. It is suggested that the resultant low‐latitude chorus boundary at the Ogo 6 orbit is close to the magnetic field line marking the low‐altitude boundary of the plasmasphere and may be an indicator of this plasmapause position under a wide range of magnetospheric conditions.

ELF emissions and relativistic electron precipitation

“…Although previous studies have been made that compare chorus emissions and electron precipitation, the number of such comparisons and the conditions represented are limited, Oliven and Gurnett [1968] have reported general association between VLF chorus and electron precipitation microbursts based on satellite observations of fields and particles and balloon X ray measurements. Similar comparison of satellite ELF chorus and electron precipitation observations has been reported by Holzer et al [1974], also with only a general correlation. This latter work showed evidence of spatial separation between emissions and particles at low altitudes as a result of wave refraction.…”

A comparative ray‐trace study of whistler ducting processes in the Earth’s plasmasphere

“…Ducting processes rely on the interplay of these two effects to constrain the ray path along the field direction to the conjugate ionosphere. This is consistent with satellite [Holzer et al, 1974] VLF wave observations. Figure 1 illustrates characteristic ray paths for various ducting pro-•es, with a perturbation number density 20% larger than the background.…”

Hiss-triggered chorus emissions at Indian stations

“…This gave an indication of the common source of emissions in the equatorial region, although there is a relatively large spatial size of the emission occurrence region in the ionosphere (2000-3000 km). The observation of VLF emissions on ground stations separated by large distances may be caused both by a direct illumination from the magnetospheric source (Holzer et al, 1974) or by a wave-guide propagation in the ionosphere (Gross, 1970). Thus, VLF emissions generated in the equatorial zone of higher L-values may propagate in ducted mode though the plasmasphere and illuminate wide region of the upper ionosphere.…”