Global Electron Content in the 23rd and 24th Solar Cycles

In the study we analyze the ionospheric global electron content (GEC) behavior during the 23rd and 24th cycles of solar activity. Global electron content is a parameter equal to the total number of electrons around the globe. The calculation of GEC is based on the data of global ionospheric maps (GIM). We consider the dynamics of GEC, as well as main regular variations in its spectrum, such as annual, semi-annual, 27-day and diurnal. The same approach is applied for the regional electron content (REC) in mid-latitude regions in Japan and Australia. General dynamics of REC, GEC and amplitude of their variations are shown to closely repeat the changes in the solar radio flux at 10.7 cm wavelength (F-10.7). The highest values of GEC at the maximum of the 24th solar cycle are 15-20 TECU lower than at the maximum of the 23rd one. The strongest dependence on the level of solar activity is observed for semiannual variations: their amplitude in the maxima and minima of a solar cycle differs by more than 10 times. For annual variations this difference is less (by 3{4 times). Unlike the semiannual, the annual variations of GEC and REC in the Northern Hemisphere region are phase-shifted, reflecting interhemispheric asymmetry. This implies that the Southern Hemisphere contributes to GEC more significantly. The dependence of REC diurnal variation amplitude on F(10.)7 index is close to linear in the region of Japan. For GEC and REC in Australia region the saturation effect with solar activity growth is revealed. The effect in GEC is due to a significant contribution of equatorial regions, in Australia region the reason for saturation effect appearance is unclear.