The Nature of Spread?F Irregularities in Antarctica

Abstract

Some characteristics of spread.F ionograms from the Antarctic region are discussed. Very disturbed periods, such as when magnetic storms are in progress, have been neglected in this analysis. Two important characteristics are the frequent occurrence of resolved as well as diffuse traces, and the appearance from time to time of an enhanced trace which seems to be produced by signals that arrive from directions close to the magnetic field direction. Two independent sets of spread�F traces are reported. Several possible models are examined and some ray tracing performed. The analysis favours a model that incorporates kinking of the contours of equal ionization density to produce "wavelengths" in the ionospheric structure of some tens of kilometres. Because of the similarities at mid and high latitude regions, it is suggested that similar mechanisms are operating at both regions to produce spread-F