Contribution of solar quiet (Sq) daily current variations to the deep earth conductivity within the Southern African Region

Abstract

This work focuses on determining the source current systems by applying the method of spherical harmonic analysis (SHA) to geomagnetic field data obtained from ground measurements. The objectives are to establish the mantle conductivity-depth profile and to compare the results of the profiles from four stations with other research findings. The study utilizes magnetometer data obtained for the year 2011 from geomagnetic stations located in Hermanus, Maputo, Tsumeb, and Hartebeesthoek within the Southern African region. The Gauss SHA method, along with Matlab software, is employed to separate the internal and external field contributions to solar quiet (Sq) current variations. Subsequently, a transfer function is used to calculate the electrical conductivity-depth profile of the region. The results show that, across all the stations, the highest seasonal Sq current was recorded in the month of June for Hartebeesthoek, Hermanus, and Tsumeb regions. Maputo, however, exhibited an exception with nearly triple peaks in the months of March, June, and December, with the highest occurring during the December solstice. The evaluated maximum values for seasonal Sq current in Hartebeesthoek, Hermanus, Maputo, and Tsumeb are approximately 16.0, 12.5, 12.0, and 14.8 nT, respectively. An equinoxial maximum with a value of 2.1 × 103 A was observed in the seasonal external Sq current in March within the Maputo region, while a solsticial minimum with a value of 0.75 × 103 A occurred in June in the Hartebeesthoek region. The seasonal separated external Sq current system pattern appears to be the same as that of the seasonal Sq current system, indicating that the source of the Sq current system is external to the Earth. The study reveals the greatest depth of Sq current penetration and the highest electrical conductivity values within the Southern African region when compared with other research. Finally, this research contributes to establishing the electrical conductivity of Maputo and Hartebeesthoek regions, where no prior work has been conducted.