GLOBAL ONSET AND PROPAGATION OF LARGE-SCALE TRAVELING IONOSPHERIC DISTURBANCES AS A RESULT OF THE GREAT STORM OF 13 MARCH 1989

Exceptionally large auroral disturbances, associated with the sunspot maximum, occurred on 12-14 March 1989, culminating in severe substorm activity between 12:00 and 15:00 U.T., on 13 March 1989 when the planetary magnetic K(p)-index was 8+ and auroral electrojet index (AE) reached a value of 2000 nT. The global effect of the substorm was particularly evident from large rises of the virtual height of the F-region (h'F) and from large ionization depletions found from the critical frequency (foF2) decreases of the layer, using data from 46 ionosonde stations. The fluctuations in h'F showed a significant correlation with auroral surges, deduced from the AE index. The evidence of sequential enhancements in h'F and associated ionization depletions, indicated the presence of large-scale travelling disturbances (LSTIDs) launched during the disturbed period and propagating to low latitudes. LSTIDs moved with velocities between 460 and 530 m s-1, originating equatorwards of the auroral zone at the shell with an L-value = 2.3. The exceptionally large and rapid enhancements in h'F, with the height increments exceeding 200 km and reaching 400 km, as well as the shift of the origin of LSTIDs to higher mid-latitudes, are the unusual aspects of the present disturbances, distinguishing them from other cases of LSTIDs studied on the global scale. The storm-induced height rises were strongly affected by the diurnal conditions and only the ionosonde stations positioned in the night-time sector of the Earth indicated the presence of pronounced increments in h'F from high to low latitudes.