Longitudinal variations of the noon f0F2 values at mid latitudes in the northern hemisphere: seasonal and solar activity dependence

Median midday values of f0F2, measured during 1958, 1964-69, 1976-78, 1980-81 at a network of ionospheric stations, located in the region of 38-69 deg N latitudes, are classified into an empiric model reflecting their variations along the circle of geographic latitude in the form of a sum of two harmonics with zone wave numbers 1 and 2. Dependence of amplitudes and phases of these harmonics and, finally, longitudinal behaviour of f0F2 on the season and the level of solar activity is studied. It is shown that longitudinal variations of f0F2 midday values are insufficient in winter, grow notably by the periods of equinoxes, especially vernal one, and during all seasons except winter, increase with solar activity growth