Investigation of the variation of the ionospheric critical frequency (foF2) with latitude

In this study, the daily variations of the critical frequency (foF2) of the F2-layer of the ionosphere obtained from the Kashima station on 10 October 1978 are investigated for 90?N and 90?S latitudes and 30?, 35?, 40?, 45?E longitudes by using generated maps. It is observed that the values of the critical frequency increases at 06.00-07.00 hours and decrease gradually at 15.00-17.00 hours. The troughs in the dip equator and the crests between +20 and -20 latitudes occurred in the latitudinal variations of the electron density distributions are also appeared in the latitudinal variations of the critical frequency at 20.00 hours. The latitudinal-longitudinal distribution of the critical frequency characteristically corresponds to the latitudinal-longitudinal distribution of the electron density at 06.00-17.00.