Statistical study of the equatorial F₂layer critical frequency at Ouagadougou during solar cycles 20, 21 and 22, using Legrand and Simon’s classification of geomagnetic activity

Abstract

This paper presents the statistical analysis of the diurnal variations of the F layer at the equatorial station of Ouagadougou (Lat: 12.4°N; Long: 358.5°E; dip: 5.9°) from 1966 to 1998 (=>~11 680 days). We consider three main factors of variability: (1) the season (spring, summer, autumn and winter), (2) the phase of the sunspot cycle (ascending, maximum, descending and minimum) and (3) the geomagnetic activity classified by Legrand and Simon in four groups: slow solar wind, high solar wind streams, fluctuating solar wind and shock activity. We easily identify the influence of the solar wind speed and shock activity on the diurnal pattern of the F layer. Shock and recurrent activities tend to enhance or diminish the morning or afternoon maximum of the F2 layer critical frequency. The difference of the diurnal foF2 variation during the increasing and decreasing phases of the sunspot solar cycle is explained by different solar wind regimes. The slow solar wind dominates during the increasing phase of the sunspot cycle and the fluctuating solar wind dominates during the decreasing phase of the sunspot cycle. This paper demonstrates that it is possible using a large database, to bring up significant morphologies of the diurnal variation of the foF2 critical frequency as a function of (1) different solar events such as quiet solar wind, fluctuating wind, recurrent high stream wind and Coronal Mass Ejections (CMEs); (2) solar cycle phases and (3) seasons. It is an approach directly connecting the critical frequency of the F2 layer to the solar parameters.

Long‐term trend of foF2 at a West African equatorial station linked to greenhouse gas increase and dip equator secular displacement

“…There are several studies on the variability of f o F 2 measured at Ouagadougou [ Ouattara et al ., ; Akala et al ., ; Ouattara et al ., ; Ouattara and Amory‐Mazaudier , ]. Long‐term trends in f o F 2 , at different times of day and seasons measured at this ionospheric station have also been studied by Ouattara [].…”

Dynamics of sunspot cycle ascending and descending phases asymmetry in equatorial ionospheric variability

“…The years used and the corresponding sunspot number are presented in Table 1. The years were classified into four epochs according to Ouattara and Amory-Mazaudier (2012). The year of solar maximum used is a good representation of very high solar activity.…”

Statistical Study of foF2 Diurnal Variation at Dakar Station from 1971 to 1996: Effect of Geomagnetic Classes of Activity on Seasonal Variation at Solar Minimum and Maximum

“…To perform the statistical hourly foF2 values we follow Ouattara and Amory Mazaudier [9] method. Therefore, the following equations are used:…”

“…Geomagnetic activity, defined as the disturbance of the geomagnetic field due to external source [1], has been divided into four classes of activity [2]- [5] These classes are: quiet activity due to slow solar wind, shock activity due to CMEs (Coronal Mass Ejections), recurrent activity provoked by high speed solar wind coming from coronal hole and fluctuating activity constituted by the other activities which are not clear [4]. The impact of each class of activity in the critical frequency of F2 layer (foF2) has been study through Ouagadougou station (Lat: 12.4˚N; Long: 358.5˚E; dip: 1.43˚) foF2 variability [6]- [9] and Dakar (Lat: 14.8˚N; Long: 342.6˚E, dip: 8.44˚) station foF2 variability [10]. The first foF2 statistical variation for an African Equatorial Ionization Anomaly (EIA) station has been performed by Ouattara and Amory Mazaudier [9] at Ouagadougou station located at the trough of ionization.…”

“…The impact of each class of activity in the critical frequency of F2 layer (foF2) has been study through Ouagadougou station (Lat: 12.4˚N; Long: 358.5˚E; dip: 1.43˚) foF2 variability [6]- [9] and Dakar (Lat: 14.8˚N; Long: 342.6˚E, dip: 8.44˚) station foF2 variability [10]. The first foF2 statistical variation for an African Equatorial Ionization Anomaly (EIA) station has been performed by Ouattara and Amory Mazaudier [9] at Ouagadougou station located at the trough of ionization. This paper, the second one that focuses on foF2 statistical variation concerns Dakar station situates between the crest and the trough of the EIA region of African sector from 1971 to 1996.…”