In this paper, we review on diurnal variations of the foF2 ionospheric parameter predicted by the IRI-2012 model, and data from Ouagadougou ionosonde station located in the crest of the Equatorial Anomaly (Lat: 12.5°N; Long: 358.5°E, dip: 1.43°) during fluctuating geomagnetic activity conditions for the solar cycles 21 and 22. Our investigations are focused on the electrodynamic aspects, the influence of the ionospheric electric currents as well as the variations of the hourly values given by model and experimental measurements. A comparative study pointed out that the IRI-2012 model, through its URSI and CCIR subroutines, gives a good prediction of the critical frequency of the F2 layer between 0700 TL and 0000 TL. In addition, IRI -2012 tries to reproduce, as best as possible, the vertical drift E × B during minimum, decreasing phase, winter, and autumn. However, there is no effect of drift during the other seasons and solar cycle phases. A last, the model does not take into account the PRE phenomenon observed in autumn and the influence of the equatorial electrojet in this ionospheric zone.ReferencesAcharya R., Roy B., Sivaraman M.R., 2010. Dasgupta A. An empirical relation of daytime equatorial total electron content with equatorial electrojet in the Indian zone. J Atmos Terr Phys, 72(10), 774–780.Acharya R., Roy B., Sivaraman M.R.; Dasgupta A., 2011. On conformity of the EEJ based Ionospheric model to the Fountain effect and resulting improvements. J Atmos Terr Phys, 73, 779-784.Adeniyi J.O., Oladipo O.A., Radicella S.M., 2005. Variability of fof2 and comparison with iri model for an equatorial station. The Abdus Salam International Centre for Theoretical Physics, IC/2005/085, http://www.ictp.it/~pub_off.Adeniyi1 J.O., Oladjipo O.A., Radicella S.M., 2005. Variability of foF2 and comparison with IRI model for an equatorial station. The Abdus Salam International Centre for Theoretical Physics, IC/2005/085.Bilitza D., et al., 2014. The International Reference Ionosphere 2012-a model of international collaborationI. J. Space Weather Space Clim, 4, A07.Bilitza D., Reinisch B.W., 2008. International Reference Ionosphere 2007: Improvements and new parameters. Adv. Space Res, 42, 599–609.Farley D.T., Bonell E., Fejer B.G., Larsen M.F., 1986. The Prereversal Enhancement of the Zonal Electric Field in the Equatorial Ionosphere. J Geophys Res, 91(A12), 13,723–13,728.Faynot J.M., Villa P., 1979. F region at the magnetic equator. Ann Geophys, 35, 1–9.Fejer B.G., 1981. The equatorial ionospheric electric fields: A review. J Atmos Terr Phys, 43, 377.Fejer B.G., Farley D.T., Woodman R.F., Calderon C., 1979. Dependence of equatorial F region vertical drifts on season and solar cycle. J Geophys Res, 84, 5792.Legrand J.P., Simon P.A., 1989. Solar cycle and geomagnetic activity: A review for geophysicists. Part I. The contributions to geomagnetic activity of shock waves and of the solar wind. Ann. Geophys, 7, 565–578.Obrou K.O., 2008. Contribution à l’amélioration du modèle "International Reference Ionosphere" (IRI) pour l’ionosphère équatoriale. Thèse de doctorat Université de Cocody, Abidjan, Côte d’Ivoire.Ouattara F., 2009. Contribution à l’étude des relations entre les deux composantes du champ magnétique solaire et l’Ionosphère Equatoriale. Thèse de Doctorat d’Etat ès Sciences, Université Cheikh Anta Diop, Dakar, Sénégal.Ouattara F., 2013. IRI-2007 foF2 Predictions at Ouagadougou Station during Quiet Time Periods from 1985 to 1995. Archives of Physics Research, 4, 12–18.Ouattara F., Amory-Mazaudier C., 2009. Solar–geomagnetic activity and Aa indices toward a Standard. J. Atmos. Terr. Phys, 71, 1736–1748.Ouattra F., Nanéma, 2014. Quiet Time foF2 Variation at Ouagadougou Station and Comparison with TIEGCM and IRI-2012 Predictions for 1985 and 1990. Physical Science International Journal, 4(6), 892–902.Oyekola O.S., Fagundes P.R., 2012. Equatorial F2-layer variations: Comparison between F2 peak parameters at Ouagadougou with the IRI-2007 model. Earth, Planets Space, 64, 553–566.Rishbeth H., 1971. The F-layer dynamo. Planet, Space Sci, 19, 263.Vassal J.A., 1982. The variation of the magnetic field and its relationship with the equatorial electrojet in Senegal Oriental. Annals of Geophysics, Tome French, 38.Zerbo J.L., Amory-Mazaudier C. Ouattara F., Richardson J., 2012. Solar Wind and Geomagnetism, toward a Standard Classification 1868-2009. Ann Geophys, 30, 421–426. http://dx.doi.org/10.5194/angeo-30-421-2012.Zerbo J.L., Amory-Mazaudier C., Ouattara F., 2013. Geomagnetism during solar cycle 23: Characteristics. J. Adv. Res, 4(3), 265–274. Doi:10.1016/j.jare.2013.08.010.Zerbo J.L., Ouattara F., Zoundi C., Gyébré A., 2011. Solar cycle 23 and geomagnetic activity since 1868. Revue CAMES serie A, 12(2), 255–262.
Geomagnetic activity is characterized by four solar wind conditions. Each condition has specific impact on ionosphere. This paper review on fluctuating activity effects on ionosphere F2 layer through its critical frequency foF2 variations. Under fluctuating wind conditions, we have investigated on annual, diurnal and seasonal variations of foF2 during solar cycles 21 and 22 phases covered by Ouagadougou ionosonde station data (Lat: 12.5˚N; Long: 358.5˚E; dip: 1.43˚). Our investigations show that foF2 annual' variability is in phase with solar cycle. The diurnal variation is "noon bite out" most of the time except for the solar maximum where we have a morning peak testifying to the fact that the vertical drift E × B is disturbed. The seasonal variations show that the fluctuating activity has no particular effect on certain characteristics of the equatorial ionosphere such as electrojet and vertical drift E × B. However, the increase of the electric field pre-reversal phenomenon in autumn is a characteristic effect observed during the fluctuating activity.
This paper investigates the performance of the latest International Reference Ionosphere model to predict the critical frequency at low latitudes in the African region. The variability of the critical frequency of the F2 layer of the ionosphere (foF2) is studied for the different seasons of the phase minimum of solar cycle 22 during quiet geomagnetic activity at the Ouagadougou station. The data used are those provided by the ionosonde and the predictions of the two subprograms: International Radio Consultative Committee (CCIR) and International Radio-Scientific Union (URSI) of the 2016 version of the International Reference Ionosphere model. This study shows that, in general, URSI and CCIR of the IRI-2016 model are able to reproduce fairly well the variability of the critical frequency of the F2 layer of the ionosphere at low latitudes during the phase minimum at the Ouagadougou station. However, the model shows an almost homogeneous overestimation of the foF2 during the four seasons studied. The good response is observed between 0700 TL and 1900 TL for the available data. The agreement between the subroutine responses and the observed results is between reasonable and poor. The best match state response is obtained in winter with the CCIR subroutine. These results show that there is a need to improve both CCIR and URSI subroutines of the IRI-2016 model in low latitudes in the African region.
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