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Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 35, 39-51, 2017
https://doi.org/10.5194/angeo-35-39-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Regular paper
04 Jan 2017
Induction effects of geomagnetic disturbances in the geo-electric field variations at low latitudes
Vafi Doumbia1, Kouadio Boka1, Nguessan Kouassi1, Oswald Didier Franck Grodji1, Christine Amory-Mazaudier2,3, and Michel Menvielle4 1Laboratoire de Physique de l'Atmosphère, Université Felix Houphouet Boigny, Abidjan, Côte d'Ivoire
2LPP, CNRS, Ecole polytechnique, UPMC Univ Paris 06, Univ. Paris-Sud, Observatoire de Paris, Université Paris-Saclay, Sorbonne Universités, PSL Research University, 4 place Jussieu, 75252 Paris, France
3International Center for Theoretical Physics, Trieste, Italy
4Université Versailles St-Quentin; CNRS/INSU, LATMOS-IPSL, 4 Avenue de Neptune, 94107 Saint-Maur-des-Fossés, France
Abstract. In this study we examined the influences of geomagnetic activity on the Earth surface electric field variations at low latitudes. During the International Equatorial Electrojet Year (IEEY) various experiments were performed along 5° W in West Africa from 1992 to 1995. Among other instruments, 10 stations equipped with magnetometers and telluric electric field lines operated along a meridian chain across the geomagnetic dip equator from November 1992 to December 1994. In the present work, the induced effects of space-weather-related geomagnetic disturbances in the equatorial electrojet (EEJ) influence area in West Africa were examined. For that purpose, variations in the north–south (Ex) and east–west (Ey) components of telluric electric field were analyzed, along with that of the three components (H,  D and Z) of the geomagnetic field during the geomagnetic storm of 17 February 1993 and the solar flare observed on 4 April 1993. The most important induction effects during these events are associated with brisk impulses like storm sudden commencement (ssc) and solar flare effect (sfe) in the geomagnetic field variations. For the moderate geomagnetic storm that occurred on 17 February 1993, with a minimum Dst index of −110 nT, the geo-electric field responses to the impulse around 11:00 LT at LAM are Ex =  520 mV km−1 and Ey =  400 mV km−1. The geo-electric field responses to the sfe that occurred around 14:30 LT on 4 April 1993 are clearly observed at different stations as well. At LAM the crest-to-crest amplitude of the geo-electric field components associated with the sfe are Ex =  550 mV km−1 and Ey =  340 mV km−1. Note that the sfe impact on the geo-electric field variations decreases with the increasing distance of the stations from the subsolar point, which is located at about 5.13° N on 4 April. This trend does not reflect the sfe increasing amplitude near the dip equator due the high Cowling conductivity in the EEJ belt.

Citation: Doumbia, V., Boka, K., Kouassi, N., Grodji, O. D. F., Amory-Mazaudier, C., and Menvielle, M.: Induction effects of geomagnetic disturbances in the geo-electric field variations at low latitudes, Ann. Geophys., 35, 39-51, https://doi.org/10.5194/angeo-35-39-2017, 2017.
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The electrical inductions within the Earth surface due to geomagnetic field variations were examined. For that purpose the records of the geomagnetic and geo-electric field variations observed in West Africa were used. We have found that the geomagnetic field brisk variations induce non-negligible geo-electric field variations at low latitudes. This result implies a possible intense geomagnetically induced current flow in the vicinity of the equatorial electrojet influence area.
The electrical inductions within the Earth surface due to geomagnetic field variations were...
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