There are presented the global distributions of electron density ne maxF2 and height hmaxF2 of the main maximum of ionosphere. There are analyzed the basic regularities of longitude-latitudinal variations of these parameters in the northern and southern hemispheres. The main attention is given to the effect of seasonal anomaly. It is shown that, according to calculations by the CCIR model seasonal anomaly appears at latitudes between 15 and 60 degrees N. approximately from 9 to 12 hours of local time. In the southern hemisphere the seasonal anomaly is not observed.
