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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 26, issue 7
Ann. Geophys., 26, 1777–1792, 2008
https://doi.org/10.5194/angeo-26-1777-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 26, 1777–1792, 2008
https://doi.org/10.5194/angeo-26-1777-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.

  26 Jun 2008

26 Jun 2008

Equinox transition at the magnetic equator in Africa: analysis of ESF ionograms

B. J.-P. Adohi1, P. M. Vila2, C. Amory-Mazaudier2, and M. Petitdidier2 B. J.-P. Adohi et al.
  • 1Université de Cocody, Laboratoire de Physique de l'Atmosphère, 22 BP 582 Abidjan 22, Ivory Coast
  • 2Centre National de la Recherche Scientifique/Université Versailles Saint-Quentin en Yvelines, Centre d'Etude des Environnements Terrestre et Planétaires, 4 avenue de Neptune, 94107 Saint-Maur-des-Fossés Cedex, France

Abstract. We study equatorial night-time F layer behaviour from quarter-hourly ionograms at Korhogo/Ivory Coast (9.2° N, 5° W, dip lat. −2.4°) during local Spring March–April 1995, declining solar flux period, according to the magnetic activity. The height and thickness of the F-layer are found to vary intensely with time and from one day to the next. At time of the equinox transition, by the end of March, a net change of the nightly height-time variation is observed. The regime of a single height peak phase before 22 March changes to up to three main F-layer height phases after 30 March, each associated to a dominant mechanism. The first phase is identified to the post-sunset E×B pulse, the second phase associated to a change in the wind circulation phenomenon and the third one attributed to pre-sunrise phenomena. The influence of the magnetic activity is identified by the increase in the second peak amplitude. After the 21 April magnetic-equinox period, the height-time morphology becomes more irregular suggesting meridional wind abatement. The initiation, the growth and the maintenance of ESF are explored in relation to these nightly variations. The Rayleigh-Taylor instability is clearly identified as main precursor phenomenon. This is followed by the P-type (F-layer peak spread) structures, the whole with no specific dependence on the magnetic activity and on the F-layer phases, in contrast to further I and F-type (Inside and Frequency spread) ESFs. We discuss our results in the light of recent advanced experiments in Peru and the pacific.

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