IONOSPHERIC EFFECTS OF THE MARCH 13, 1989, MAGNETIC STORM AT LOW AND EQUATORIAL LATITUDES

The great geomagnetic storm of March 13, 1989 (SIGMA-Kp = 60, Ap = 246) caused severely anomalous behaviour in the equatorial and low latitude ionosphere in the Brazilian longitude sector. The ionograms over Fortaleza (4-degrees-S, 38-degrees-W) indicated F region upward plasma drifts exceeding 200 m s-1 at 1830 LT as compared to normal values of 40 m s-1 for this epoch. Large negative phases were observed in foF2 over Fortaleza and Cachoeira Paulista (22.5-degrees-S, 45-degrees-W) and in total electron content measured over Sao Jose dos Campos (23-degrees-S, 46-degrees-W). The equatorial ionization anomaly was totally absent either because of its anomalous expansion to higher latitudes or because of inhibition of its development on the two nights following the storm. Many anomalous variations in F region peak density and height, occurring simultaneously with sharp variations on H component of magnetic field over Fortaleza and with auroral substorms, give strong evidence of penetration of magnetospheric electric fields to equatorial and low latitudes. Auroral type sporadic E and night E layers are observed after 1830 LT over Cachoeira Paulista, the latter showing peak electron density of about 6 x 10(4) el cm-3, therefore comparable to the E layer peak density in the morning hours at that station. The Fortaleza ionograms show the presence of the F1 layer at night, a phenomenon that has never been observed over our two stations before. The role played by electric fields penetrating from high to low latitudes, particle precipitation, and composition changes in explaining the observations is discussed.