Nighttime ionospheric saturation effect estimation in the African equatorial anomaly trough: A comparison of two approaches

Abstract Using the two‐segmented and the quadratic regression analyses methods, the existence of saturation effect in the ionospheric electron content has been established in published literatures. With data set that spans an 11 year period (one solar cycle) from an African low‐latitude station—Ouagadougou, Burkina Faso (Geographical coordinates 12 o N, 1.8 o W, dip ~3 o N)—and adopting the quadratic and the two‐segmented regression methods, we have studied nighttime saturation effect on the critical frequency of ionospheric F 2 layer ( f o F 2 ) around the magnetic dip. Both methods revealed that saturation effect in f o F 2 cuts across all seasons during nighttime. This phenomenon was least at the peak of the prereversal enhancement (PRE) period and increases significantly beyond midnight. Either of the two approaches can be adopted for saturation effect studies. The advantage of the two‐segmented over the quadratic is that the change point (breakpoint), which is the solar flux level where saturation effects first become observable, can be determined. The effect seen around the PRE period may be attributed to the E × B drift while the effect beyond the PRE period is masked by other mechanisms.