Guided echoes in the magnetosphere: Observations by Radio Plasma Imager on IMAGE

Abstract

Long-range, discrete, radio echo traces observed in the magnetosphere by the Radio Plasma Imager (RPI) on IMAGE have been interpreted as signals guided along geomagnetic field lines. During IMAGE traversals of the plasmapause and near-equatorial plasmasphere, multiple echo traces, attributed to signals reflected successively between conjugate hemispheres, are often observed. Single traces seen far beyond the plasmapause at high latitudes are attributed to guided echoes from the local hemisphere in the polar region. Here the field lines are either (1) open, (2) closed but too long to be observed within the instrument listening time or (3) closed but not able to maintain the signal-guiding conditions across the equator to the conjugate hemisphere. In this letter we present examples of guided echoes producing both the single and multiple reflection traces observed by RPI at altitudes of a few Earth radii and discuss possible guiding mechanisms.