On validating the relationship of ionogram signatures to large-scale wave structure

Abstract

The development of plasma structure in the nighttime equatorial F layer, known as equatorial spread F (ESF), appears to be influenced (if not controlled) by the presence of large-scale wave structure (LSWS). To understand this process, knowledge of the properties of LSWS is crucial. A major obstacle, in this regard, is the virtual lack of LSWS data; most instruments in use today are unable to detect spatial structure in the absence of horizontal drift. There appears to be some information about LSWS contained in two ionogram signatures, multi-reflected echoes (MREs) and satellite traces (STs). How useful they can be depends, however, on knowledge of their relationship to LSWS. Results from a case study are presented herein, which show that MREs are likely produced by a tilted, or shallowly modulated, reflecting surface in the bottomside F layer, whereas STs are produced by more steeply sloped surfaces. The accumulated results are shown to lead to a working hypothesis for LSWS development followed by ESF. Differences between LSWS and a traveling ionospheric disturbance are also pointed out.