| Popis: |
In the framework of the French-Ivorian participation to the IEEY, a network of ten electromagnetic stations were installed at African longitudes. The aim of this experiment was twofold : firstly, to study the magnetic signature of the equatorial electrojet the one hand, and secondly, to characterize the induced electric field variations on the other hand : The first results of the magnetic field investigations were presented by Doumouya and coworkers. Those of the electric field experiment will be discussed in this study. The electromagnetic experiment will be described. The analysis of the electromagnetic transient variations was conducted in accordance with the classical distinction between quiet and disturbed magnetic situations. A morphological analysis of the recordings is given, taking into consideration successively quiet and disturbed magnetic situations, with the results interroged in terms of the characterization of external and internal sources. Particular attention was paid to the effects of the source characteristics on the induced fiel of internal origin, and to the bias they may consequently cause to the results of electromagnetic probing of the earth ; the source effect in electromagnetic induction studies. During quiet magnetic situations, our results demonstrated the existence of two different sources. One of these, the S (sup E; sub R) source, was responsible for most of the magnetic diurnal variation and corresponded to the well-known magnetic signature of the equatorial electrojet. The other source (the S* (sup E; sub R) source) was responsible for most of the electric diurnal variation, and also likely to be ionospheric source. Electric and magnetic diurnal variations are therefore related to different ionospheric sources, and interpreting the electric diurnal variation as induced by the magnetic field diurnal variation is not relevant... (D'après résumé d'auteur). |
