Day-to-Day Variability of H and Z Components of the Geomagnetic Field at the African Longitudes

The Day-to-day variability of the geomagnetic field elements at the African longitudes has been studied for the year 1987 using geomagnetic data obtained from four different African observatories. The analysis was carried out on solar quiet days using hourly values of the Horizontal, , and vertical, , geomagnetic field values. The results of this study confirm that Sq is a very changeable phenomenon, with a strong day-to-day variation. This day-to-day variation is seen to be superimposed on magnetic disturbances of a magnetospheric origin. 1. Introduction Changes in the magnetic environment of the Earth are of interest to those studying space weather and climate change, particularly in the upper atmosphere. The upper atmosphere is ionized by the Sun’s ultraviolet and X-radiation to create the ionosphere, and the free ions and electrons are moved by winds arising from the heating effects of the Sun. The currents in the ionosphere have magnetic effect on the ground and are monitored using magnetometers on the Earth surface. The records of any observatory show that on some days there are regular variations on the magnetic record while on other days the variation is irregular. The daily variations of the geomagnetic field when solar-terrestrial disturbances are absent are called solar quiet (Sq) variations [1]. These Sq variations are caused mainly by electrical currents in the upper atmosphere, at altitudes of about 110？km above the Earth surface [2]. Studies on solar quiet daily variation of the Earth’s magnetic field show that Sq on one day can be different from Sq of the next day in amplitude, phase, and focal latitude [3–5]. This change in Sq between two adjacent days is the day-to-day variability in Sq between the two days. This day-to-day variability has been highly attributed to changes in the ionospheric dynamo currents, which depend on the ionospheric conductivity and tidal winds, varying with solar radiation and ionospheric conditions [6, 7]. Hasegawa [8] examined the day-to-day changes of the quiet day variation and the ionospheric current systems for the second polar year and suggested that some or all the day-to-day variabilities in solar quiet daily variation (Sq) are due to variability in the positions of the foci of the ionospheric current systems rather than changes in the distribution of ionization and conductivity. Studies conducted by [9–16] clearly showed that the variability of Sq occurred at all hours of the day. Rabiu et al. [17] from their comprehensive study of Sq day-to-day variability at Addis Ababa, an equatorial electrojet