Abstract:

Ionograms and magnetograms at Great Wall (62°13′S,58°58′W),Antarctica,were used to study the sub auroral ionospheric effects of the March 13,1989 magnetic storm.The virtual height of the F region (h′F) increased and the critical frequency(f 0F 2) decreased rapidly just after the storm's 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 0F 2 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 7.5×10 5el cm -3 .The causes of these phenomena are discussed. Behaviours of h′F and f 0F 2 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 occure, and the longer the depressions of f 0F 2 last.