Ionosphericƒ0F2 values and their gradients at European longitudes

Ionospheric f o F 2 values were deduced from vertical ionograms taken near the maximum of the current solar cycle at three European locations during 1990-1991: Dourbes, Belgium (50.1°N, 4.6°E); Roquetes, Tarragona, Spain (40.8°N, 0.3°E); and Rome, Italy (41.9°N, 12.5°). The three stations form a nearly equilateral triangle with a base distance of ∼1100 km. Diurnal, day-to-day, as well as seasonal variations are evident for the parameter and its gradients. Cross-correlation analysis was performed to assess the predictability of the ionospheric variability at one locale based on realtime measurement at another