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In this paper the daytime vertical E → × B → drift velocity in the F-region of the equatorial ionosphere was estimated from the magnetic effect of the equatorial electrojet (EEJ) in West African sector for September equinoxes in 1993 during solar cycle 22 and in 2013 during solar cycle 24. Geomagnetic data recorded during the International Equatorial Electrojet Year (IEEY) from 1993 to 1994 and the ongoing AMBER (African Meridian B-field Education and Research) program since 2008 were used. The vertical drift velocity was inferred from the EEJ contribution ( Δ H ) in the geomagnetic field horizontal component. The IEEY data were used to examine the seasonal variations of the daytime vertical drift velocity. The noontime seasonal averages are Vd = 10.95 m / s and Vd = 9.46 m / s respectively for March and September equinoxes, and Vd = 8.75 m / s and Vd = 8.27 m / s for December and June solstices. The daytime vertical drift velocity was found to be larger in equinoxes than in solstices. The dependence of the daytime vertical drift velocity on solar cycle was also shown by comparing the results of September equinox in 1993 and 2013. The drift velocity of 9.5 m/s in 1993 is significantly weaker than that of 24.5 m/s in 2013. This strong difference in Vd reflects the level of solar cycle between 1993 when the mean F10.7 = 109.86 sfu and 2013 when the mean F10.7 = 122.55 sfu.

International audience; During the International Equatorial Electrojet Year (IEEY), an IPS-42 ionosonde located at Korhogo (9.33°N, 5.42°W, -1.88°dip-lat) and a meridian chain of 10 magnetic stations were setup in West Africa (5°West longitude). In this work, some characteristic parameters of the equatorial electrojet were estimated on the basis of the IPS-42 ionosonde data at Korhogo during the years 1993 and 1994. The study consisted of determining the zonal electric field through an estimate of the plasma vertical drift velocity. The daytime plasma vertical drift velocity was estimated from the time rates of change of the F-layer virtual height variations and a correction term that takes into account the ionization production and recombination effects. This method resulted in an improved vertical drift velocity, which was found to be comparable to the results of previous studies. The estimated vertical drift velocity was used in a semi-empirical approach which involved the IRI-2012 model for the Pedersen and Hall conductivities and the IGRF-10 model for the geomagnetic main field intensity. Thus the zonal and polarization electric fields on one hand, and the eastward Pedersen, Hall and the equatorial electrojet current densities on the other hand, were estimated. Furthermore the integrated peak current density at the EEJ center was estimated from ionosonde observations and compared with that inferred from magnetometer data. The integrated EEJ peak current densities obtained from both experiments were found to be in the same order and their seasonal variations exhibit the same trends as well.

The determination of the physical parameters of the equatorial electrojet (EEJ) from Korhogo (Latitude +9.3; Longitude −5.4; Dip −0.67) during the period of 1993 to 1994 was carried out by data of ionosonde IPS-42. The results made it possible to show that for a low average value of electron drift vertical approximately 5 m/s to the solstices and 6 m/s with the equinoxes in the morning, we obtained around midday a strong density of current of the EEJ (3.30A/km2 in 1993 and 2.6A/km2 in 1994). We determined during this study the values of the various electric fields intervening in the mechanism of formation of the EEJ. We showed the strong contribution of the polarization electric field in this phenomenon. The results gave the values of the zonal and polarization electric fields respectively 0.19mV/m and 3.5mV/m. The data of ionosonde IPS-42 made it possible to determine the density and intensity of current center of the EEJ (I 0 = 231.11±53.7 A/km). We compared the intensity of the current in the center obtained with the ionosonde with that of the data on the ground. We obtained appreciably similar results.