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

Ali Mahamat Nour,Ouattara Frédéric,Nanéma Emmanuel,Zerbo Jean Louis,Zougmoré François,Gyébré Aristide Marie Frédéric

doi:10.4236/ijg.2015.63014

Abstract

The statistical study of F2 layer critical frequency at Dakar station from 1971 to 1996 is carried out. This paper shows foF2 statistical diurnal for all geomagnetic activities and all seasons and that during solar maximum and minimum phases. It emerges that foF2 diurnal variation graphs at Dakar station exhibits the different types of foF2 profiles in African EIA regions. The type of profile depends on solar activity, season and solar phase. During solar minimum and under quiet time condition, data show the signature of a strength electrojet that is coupled with intense counter electrojet in the afternoon. Under disturbed conditions, mean intense electrojet is observed in winter during fluctuating and recurrent activities. Intense counter electrojet is seen under fluctuating and shock activities in all seasons coupled with strength electrojet in autumn. In summer and spring under all geomagnetic activity condition, there is intense counter electrojet. During solar maximum, in summer and spring there is no electrojet under geomagnetic activity conditions. Winter shows a mean intense electrojet. Winter and autumn are marked by the signature of the reversal electric field.

Highlights

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 first frequency of F2 layer (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
We present foF2 diurnal variation during solar minimum and maximum phases under the four geomagnetic conditions and for different seasons

Summary

Introduction

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 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. To contribute to space weather study by determining ionosphere variability under different types of solar activity and that for different seasons and solar cycle phases. Dakar station is used because foF2 variation comparative study through its long term trend variation and diurnal variation shows the particularity of Dakar station (see [11]-[13]). Our attention is only focused on foF2 statistical diurnal variation during solar minimum and maximum phases

Methods

Results

Conclusion