Ionospheric Effects of the March 13, 1989 Magnetic Storm at Sub-Auroral Region

Abstract

Ionograms and magnetograms at Great Wall (62°13'S, 58°58'W), Antarctica, were used to study the ionospheric effects of the March 13, 1989 magnetic storm in sub-auroral locations. The virtual height of the F region (h'F) increased and the critical frequency (f_oF₂) decreased rapidly just after the storm sudden commencement (SSC). Then the spread F appeared and lasted about five hours. During the main phase of the magnetic storm the ionosphere encountered severe absorptions, but large enhancements in h'F and associated depressions in f_oF₂ sometimes were still observed. On the second and third nights after the SSC auroral type sporadic E and night E layers were observed, showing peak electron densities as high as 7.5 × 10⁵ el cm^-3. The causes of these phenomena are discussed. Behaviours of h'F and f_oF₂ from four ionosonde stations in the same longitude sector (Great Wall, Port Stanley, Cachoeira Paulista and Fortaleza) show that the higher the station's latitude is, the more severe absorptions occur, and the longer the depressions of f_oF₂ last.