Abstract
Abstract. In the framework of the French participation in the International Equatorial Electrojet Year (IEEY), ten magnetotelluric stations were installed between November 1992 and November 1994 along a 1200-km-long meridian profile, between Lamto (latitude 6.2°N, Côte d'Ivoire) to the south and Tombouctou (latitude 16.7°N, Mali) to the north. These stations measured digitally the three components of the magnetic field and the two components of the telluric electric field, and operated over a period of 20 months. The magnetic data is used to study the features of the equatorial electrojet (EEJ) in West African longitude. The measurement of the telluric electric field variations will be presented elsewhere. Hourly mean values are used to study the morphological structure of the regular diurnal variation SR of the three components (H, D, and Z) of the earth magnetic field and to characterize the EEJ during magnetically quiet days. The occurrences of the counter-electrojet (CEJ) are set forth, emphasizing its seasonal variability. Assumed to be a current ribbon, the EEJ main parameters (the position of its center, its width, and the amplitude of its current density at the center) are determined. A preliminary analysis of the time variations of these parameters is presented over period of 20 months (from January 1993 to August 1994). Results are compared with those obtained during previous experiments of the same kind.
Highlights
An early observation, at Huancayo in 1922, of the enhancement of the magnetic diurnal variation near the geomagnetic equator was attributed to a narrow ionospheric current which was later named by Correspondence to: J
This paper presents the ®rst results obtained from data of ten magneto-telluric stations almost regularly spaced from the north of Mali to the south of Coà te d'Ivoire
Results are compared with those obtained during previous experiments of the same kind
Summary
At Huancayo in 1922, of the enhancement of the magnetic diurnal variation near the geomagnetic equator was attributed to a narrow ionospheric current which was later (in 1951) named by Correspondence to: J. This phenomenon has been studied through dierent types of experiments: its vertical structure has been investigated using instruments inside rockets (Sastry, 1970, Sampath and Sastry, 1979); its magnetic eects have been monitored with the help of meridian chains of magnetometers crossing the geomagnetic equator (Chapman, 1951, Forbush and Casaverde, 1961, Fambitakoye and Mayaud, 1976a, b, c, Hesse, 1982). V. Doumouya et al.: Equatorial electrojet at African longitudes: ®rst results from magnetic measurements pluridisciplinary program aimed at studying the EEJ. In the African longitude sector, France started a collaboration with Coà te d'Ivoire and Senegal (Amory-Mazaudier et al, 1993) The novelty of this experiment is the synchronous combination of the dierent types of measurements required to study the EEJ (ionosondes, HF radars, interferometer, and magnetometers network). We present and critically discuss former experiments designed to study the EEJ, emphasizing the scienti®c possibilities and limitations of each of them
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