Conjugate echoes in Alouette-2 topside-sounder data

Three types of ionograms containing symmetric conjugate echo traces which appear frequently in the Alouette-2 satellite topside-sounder data are presented and explained in terms of multiple reflections between conjugate points of the field line passing through the satellite. Such symmetric traces have not been previously reported in the literature. The high intensity of these traces gives credence to the existence of magnetospheric waveguides along which signals can propagate with very little attenuation.