Scattering of terrestrial kilometric radiation at very high altitudes

Abstract

On a number of occasions during the 3.5‐yr operating lifetime of Rae 2, we observed strong terrestrial kilometric radiation when the spacecraft was over the far side of the moon and when the low‐altitude terrestrial magnetosphere was completely obscured from view. If these deep lunar occultation events are used to infer radio source locations, then we find that the apparent source must sometimes be situated at geocentric distances of 10–40 RE or more. From an analysis of these events, we show that they are probably due to propagation effects rather than the actual generation of the emission at such large distances. The kilometric radiation can be generated near the earth at auroral latitudes and subsequently strongly scattered in the magnetosheath and nearby solar wind to produce the large apparent distances. The most likely scatterers are density inhomogeneities in the magnetosheath plasma and ion plasma waves in the magnetosheath and the upstream solar wind.

Ordinary mode auroral kilometric radiation, with harmonics, observed by ISIS 1

“…A number of investigations have placed the location of this source region along auroral field lines at geocentric distances between about 1.5 and 3.5 R e [Gurnett, 1974;Kurth et ., 1975;Green et al, 1977;Alexander et al, 1979;Benson and Calvert, 1979;Gallagher and Gurnett, 1979;Morioka et al, 1981;Calvert, 1981b]. All of the AKR observations interpreted as x-mode were either made from polar orbiting satellites or from spacecraft very distant from the earth so that radiation from the polar regions could be directly received.…”

Locations of auroral kilometric radiation bursts inferred from multispacecraft wideband Cluster VLBI observations. 1: Description of technique and initial results

“…They found that the emission extended over a wider range of Earth distances from 2 to 20 Re, including the dayside cusp region. However, these surprisingly large distances were later reinterpreted as likely due to scattering, probably by density inhomogeneities in the magnetosheath [ Alexander et al , 1979].…”

The WIND‐HAARP Experiment: Initial results of high power radiowave interactions with space plasmas

“…Only a few experiments on HF wave scattering from high altitude irregularities have been done [Gurevich et al, 1992], with somewhat controversial results [Greenwald, 1994;Guterich et al, 1994] or with indications that greater detection sensitivity is needed [Hysell et al, 1997]. Previous measurements of wave scattering in space plasmas [Alexander et al, 1979] have suggested the use of spacecraft receivers be-…”