ANNALS OF GEOPHYSICS, cilt.45, no.5, ss.621-628, 2002 (SCI İndekslerine Giren Dergi)
The present study concentrate,, on the effects on the ionosphere of an individual severe magnetic Storm of the Sudden Commencement (SSC) type. with SSC taking place in the daytime hours. The storm started on 29 October 1968 and went on to 2 November 1968 with geomagnetic 3-hourly magnetic activity index reaching values of K-p greater than or equal to 7. Interplanetary magnetic field polarities included A (field polarity Away from the solar wind) positive and T(field polarity Towards the solar wind) negative polarities, In these conditions, the local response of true height of F-region (hF) ionization falls nonlinearly from fixed plasma densities. The interplanetary B-t, the magnetic field H-component and K-p were examined for the 5 days following the sudden commencement. Due to intensive geomagnetic SC effects. the lower and upper limits of the F-regions ere unbalanced because of gravity relaxation and solar wind pressure effects. until normal levels were restored. In the F-layer 70% deviations of critical frequencies (f(0)F) front median values, as well as hF level variations reaching hundreds of kilometers. were observed and were responsible for the destruction of communication channels. With a plasmapause location value L = 1.6 and with K-p greater than or equal to 7 the protonosphere reservoir should take 1.1 days for its replenishment: one day was in fact insufficient for a full plasma recovers.