Variations in ionospheric parameters during periods of minimum and maximum solar activity

Ionospheric investigations in Ukraine are being carried out with uniquely developed incoherent scatter radars. Data on the variations in the electron density and the electron and ion temperatures during periods of low (1994) and high (1989-1990) solar activity are presented. The F-layer peak height ranges from 450 at night to 240 km in the daytime; the electron density maximum varies approximately from 2.571 012 m(-3)-0.671 012 m(-3) over a cycle of solar activity throughout the winter period. The electron temperature has a maximum afternoon value as the solar activity is high in summer. In the periods of magnetic disturbances, a drop in N-e is most frequently observed. In winter, the influence of the sunrise and sunset at the magnetic conjugate point is also observed. An increase in electron temperature, a drop in electron density, and the displacement of the heated region along the magnetic field lines are clearly seen in the ionosphere irradiated by high-power, HF radiation. Longitudinal effects in the ionospheric behaviour were observed in simultaneous measurements in Kharkiv and Millstone Hill (USA).