VARIABILITY OF THE F1 IONOSPHERIC LAYER DURING PERIODS OF QUIET AND SHOCK GEOMAGNETIC ACTIVITY AT THE KORHOGO STATION

In this work, the diurnal variability of the critical frequency foF1 and the virtual height h2F1 is investigated above the Korhogo equatorial station (Cote d Ivoire) during periods of quiet and shock geomagnetic activity. The study days were identified using pixel diagrams and the classification of Legrand and Simon (1989). The analyses were conducted according to the seasons and solar phases, using mean diurnal profiles. The results show that during quiet periods, the F1 layer exhibits regular diurnal profilesthat are predominantly dome-shaped with a strong seasonal and solar dependence of foF1, confirming the dominance of photochemical processes. Conversely, during periods of shock activity, significant perturbations are observed, characterized by ionization troughs, compressions, and vertical instabilities in h F1, as well as a reduction in the lifetime of the F1 layer, particularly in summer (6 hours)and at solar maximum(8 hours). These signatures reveal the combined influence of penetrating electric fields, perturbed thermospheric winds, and enhanced recombination processes on the dynamics of the equatorial F1 layer.