Geomagnetic field variations at African equatorial regions during the ascending phase of the solar cycle 24

Abstract

The Earth’s magnetic field is the field of force that extends from the interior of the Earth to the outer space where it interconnects with the Interplanetary Magnetic Field (IMF). It is characterized by regular and irregular variations. Previous researches have shown the geomagnetic field variations at different sectors of the world. Despite the significance of knowledge on geomagnetic field variations to industry, communication and navigation as well as the localized nature of ionospheric dynamics, geomagnetic field variation studies in Africa is still not fully exploited. Therefore, knowledge gaps that this study has bridged are: the solar quiet seasonal and annual variations; the seasonal and annual variations of Equatorial Electrojet current (EEJ) strength as well as the storm time variations of the Earth’s magnetic field in the African equatorial regions during the ascending phase of the 24th solar cycle, comparing different stations within the African equatorial region. Based on the aforementioned knowledge gaps, the problem of this study was the little accessible information on the Geomagnetic field variations in the African equatorial region during the ascending phase of solar cycle 24 from the year 2009-2014 to help establish its solar quiet and storm time variations in Addis Ababa, Adigrat, Mbour and Yaoundé stations and to estimate the EEJ strength in Mbour and Addis Ababa for the period 2009 to 2014 for identification of the specific and unique trends within this region, that may be useful for industries and space agencies in the region for purposes of planning and preparations for space weather eventualities. The objectives set to be achieved by this study were: to establish the solar quiet seasonal and annual variations of Earth’s magnetic field; to determine the storm time variations of the geomagnetic field at Adigrat (ETHI) , Addis Ababa(AAE), Yaoundé(CMRN) and Mbour(MBO) during the Ascending phase of the solar cycle 24 from the year 2009 to 2014; and to estimate the seasonal and annual Equatorial Electrojet (EEJ) strength at Addis Ababa and Mbour for the period from 2009 to 2014. The Solar quiet (Sq) variations were calculated by method of non-cyclic variation and EEJ strength estimated using the two station method. The monthly values were averaged for months in a season to give seasonal variations while the average monthly values for a particular year provided the annual variations. The storm perturbations were obtained by subtracting the Sq of the most quiet day of every month from the Storm time variation of that day under study. Sq showed a seasonal variation which recorded the highest magnitudes of 110nT, 70nT, 65nT and 75nT for AAE, CMRN, ETHI and MBO respectively in the Equinoxes and lowest magnitudes of 50nT, 40nT, 40nT and 45nT for AAE, CMRN, ETHI and MBO respectively during the June solstices. Both the annual and seasonal variations showed solar activity, longitude and the local time dependence. The seasonal and annual variations in the EEJ strength showed larger magnitudes at Addis Ababa as compared to Mbour but larger peaks of westward Counter Electrojet (CEJ) current in Mbour as compared to Addis Ababa. The EEJ annual variation peaks during low solar activity years occurred earlier at about 1200LT as compared to peaks during high solar activity years which occurred between 1300LT and 1400LT, an outcome attributed to earlier ionization peaks during low solar activity leading to increased ionospheric conductivity. The storm time variation had a latitudinal variation. The results are useful for long term forecasting on the impact of geomagnetic field variations to help mitigate the effects of storms on the economic and ecological environment. This study recommends further research into the lack of seasonal variation on the CEJ in this region and the cause of the latitudinal storm time variation.