Multi-Reflected Echoes: Another Ionogram Signature of Large-Scale Wave Structure

Abstract

One or more steeply sloped traces have been found in evening ionograms taken from the Kwajalein Atoll (4.3°N dip latitude) during July 1979. Their resemblance to the normal F trace suggests that they are echoes that have undergone a large number of reflections from the F layer. These multi-reflected echoes (MREs) are interpreted in terms of focusing produced by curved isodensity contours in the bottomside F layer, which appear to be associated with large-scale wave structure (LSWS) that develops in the bottomside F layer. MREs appear to be another signature for LSWS, together with satellite traces that appear later in time, closer to the onset of plasma structure referred to as equatorial spread F. MREs are interesting because they display, for the data set examined, a strong preference to occur during the post-sunset rise of the F layer, which includes E-region sunset. How this finding affects our understanding of LSWS is discussed.