Equatorial F-layer irregularity patches at anomaly latitudes

Abstract

Recent studies of the physics of F-layer irregularities in the equatorial ionosphere have been concerned with the development of plumes or patches. A series of observations in the equatorial anomaly region in a year of high solar flux has been analyzed for the radio propagation effect of scintillations. The observations were made on patches in the developing, mature and decay phases. Although irregularities develop on the west wall of the patches, the intensity of scintillation does not appear to diminish within the patch; the patches contain bursts of high level activity. Patch characteristics at microwave wavelengths match airglow depletion images when two considerations are introduced, i.e. the westward tilt of the patch as shown by optical and radar observations and the effective path length of the irregularities affecting the radio propagation path. Using optical images of depletions the effective thickness of the layer of irregularities above the peak of the F2-layer can be estimated; it is relatively short, i.e. of the order of 70 km for the gigaHertz frequencies and 150 km for the 257 MHz transmissions. The total path length is 110 km for the microwave frequencies and 220 km for the lower levels of scintillation at 257 MHz. The decrease in microwave scintillations compared to meter wavelength observations in the midnight and post-midnight time period in these anomaly observations is due to the combination of decay of electron density as well as the relatively rapid decay of smaller scale irregularities, as has previously been noted in observations at the magnetic equator.