Comparative Analysis of Diurnal-Seasonal Variations of Ionospheric F2-Layer Parameters during the 24th Solar Activity Cycle

The ionosphere serves as the primary natural medium for radio-wave propagation over wavelengths ranging from millimeters to tens of thousands of kilometers. Understanding regular and irregular ionospheric processes, therefore, remains a critical scientific objective. At present, empirical models of wave disturbances that capture diurnal, seasonal, and longer-term global variations in their parameters do not exist. Developing such models requires consistent, continuous observations worldwide; however, because such coverage is unattainable, researchers typically focus on measurements obtained during characteristic geophysical periods, including the spring and autumn equinoxes and the summer and winter solstices. The present study follows this approach. This work reports the results of an analysis of diurnal and seasonal variations in electron density and associated wave disturbances in the ionospheric F2 layer during the 24th solar activity cycle. To monitor ionospheric conditions, we employed a custom-built digital ionosonde developed at the V. N. Karazin Kharkiv National University. After constructing time series of critical frequencies, the trend and the difference between the original series and the trend were calculated. We determined the electron density and its increment from the critical frequency of the ordinary component of the reflected signal. Across all seasons, a dominant oscillation with a period of 140–250 min, an amplitude of (3.8–11.4) × 1010 m–3, and a relative amplitude of 0.09–0.23 appeared in the F2 layer of the ionosphere. Depending on the season, this oscillation persisted for up to 12 h, whereas oscillations at other periods showed substantially smaller amplitudes. Through a comparative analysis of diurnal and seasonal variations in F2-layer electron density and its quasi-periodic disturbances, we established quantitative parameters that characterize these variations.