Abstract

Solar sources of geomagnetic activity are determined by means of (1) Mayaud aa index values from 1868 to now; (2) sudden storm commencement (SSC) dates and (3) pixel diagrams. From 1966 to 1998 that is, during 33 years severe geomagnetic storms characterised by aa > = 100 nT have been identified and their solar sources determined. During these three solar cycles (cycles 20, 21 and 22) the effects of these solar disturbance events on Ouagadougou ionosphere F2 parameters (foF2 and h’F2) variations are studied. Each disturbed F2 parameters morphology variations are computed and shown and after compared to each whole F2 parameters morphology variation. The analysis of whole and disturbed F2 parameter morphologies and their variations gives the main following results: (1) Severe storms are responsible for equinoctial anomaly in foF2; (2) shock activity causes vernal equinoctial asymmetry in foF2 and autumnal equinoctial asymmetry in h’F2; (3) fluctuating wind streams produce autumnal equinoctial asymmetry in foF2 and vernal equinoctial asymmetry in h’F2; (4) Geomagnetic activities produced negative storms from 1966 to 1981 and positive storms from 1981 to 1987; (5) For the seasonal variation we have positive storms all through the year except in April where we observe negative storms.

Key words: Coronal mass ejections (CMEs), fluctuating wind streams, equinoctial anomaly, geomagnetic activity.

Abbreviation

CMEs, Coronal mass ejections; NGDC, National Geophysical Data Center.