Analysis of the Variability of Diurnal Profiles of Critical foF2 Frequencies in the Light of Solar Radiation

This present article was written to analyze the variability of the diurnal profiles of the critical foF2 frequencies in the light of solar radiation based on in situ measurements of the ionosonde stations of Dakar (latitude 14.8° N, longitude 342.6° E) and Ouagadougou (latitude 12.5° N, longitude 358.5° E), respectively, for Sunspot Cycles 21 and 22. The objective being to deduce interpretations in terms of propensity to occur on the five profiles B, M, R, D, and P referenced to occurrence between the latitudes of 20° N and 20° S. Thus, on the analyses of conjunctions in phases or in phase shift observed in the variation of the sunspot cycle (VSC) and monthly foF2 frequencies (MFVs), we will note the following: (1) during periods of geomagnetic calm, (a) a propensity for the formation of the R profile during the growth phases of the solar cycle and during the periods from the solstices to the equinoxes and this is due to the conjunction in the growth–growth phase between VSC and MFV; (b) a propensity for the formation of the M profile during the waning phases of the solar cycle and during the periods from the equinoxes to the solstices and this is due to the conjunction in the waning–decaying phase between VSC and MFV; (c) a propensity for the formation of profiles B, D, and P on the one hand during the growth phases of the solar cycle and during the periods from the equinoxes to the solstices and on the other hand during the waning phases of the solar cycle and during the periods from the solstices to the equinoxes and all these are due to the nonconjunction in the phase between VSC and MFV. It therefore appears that out of the 16 possible propensities for profile formations, the R and M profiles are each counted for 12.5%. Profiles B, P, and D each counted 25%. (2) During periods of geomagnetic disturbances, notably by SFEs, CMEs, or ionization losses, a profile can transform into one or other of the other four profiles. Finally, as an importance or application of this study, we note that (a) foF2 contributes more to the good knowledge of the ionosphere; (b) using the diurnal profiles of foF2, we could a priori identify periods of lulls in radio or satellite transmission; (c) by induction, we could count the solar flares during the day; and (d) the proposed mathematical model is a basic tool for analyzing foF2 variability.