Mid-latitude ionospheric effects of a great geomagnetic storm

On March 13, 1989 magnetic storm effects on the mid- and low-latitude ionosphere were investigated. For this, peak electron density of 172-layer (NmF2) data from four chains of ionospheric stations located in the geographic longitude ranges 10degreesW-15degreesE, 55degreesE-85degreesE, 135degreesE-155degreesE and 200degreesE-255degreesE were used. Relative deviations of perturbed NmF2 from their respective quiet-time values were considered. Long-lasting negative storm effects were the dominant characteristic observed at middle latitudes, which occurred since the main phase of the storm. In general, the most significant negative disturbances were observed at middle-high latitudes. In the longitudinal sectors in which the storm started at day-time and pre-dusk hours, positive storm effects at middle and low latitudes were observed during the main phase. The role of some physical mechanisms to explain the ionospheric effects is also considered. (C) 2004 Elsevier Ltd. All rights reserved.