A study of day to day variability in geomagnetic field variations at the electrojet zone of Addis Ababa, East Africa

Abstract

Magnetic records obtained at low latitude geomagnetic observatory of Addis Ababa in Africa for the sunspot minimum year 1986 were analysed for day-to-day variability of the hourly amplitudes of solar daily variation in horizontal, H, and vertical, Z, geomagnetic field intensities. Direct measurement of the day-to-day variability was done using a proven differential expression. The variability was studied under quiet and disturbed conditions. Quiet day day-to-day variability has consistent and explicable diurnal and seasonal variation. The daytime magnitudes are greater than the nighttime magnitudes for all the months in the two elements. On quiet conditions, the dayto-day variability is observed to be maximum during the June solstice in the two elements. The dayto-day variability on disturbed condition is least in June solstice in both elements. The magnitudes of day-to-day variability had the following annual mean values: SV(Hq) = 12.7934 + 4.1346 nT, SV(Zq) = 2.9123+ 0.7178 nT, SV(Hd) = 33.4002+ 20.6256 nT, SV(Zd) = 3.8637+ 1.2450 nT. The daily mean SV on disturbed condition is generally greater than those of quiet conditions for same elements. The annual mean SV is greater in element H at any given condition. Seasonal change in the Sq variation is explicable in terms of seasonal shift in the mean position of the Sq current system of the ionospheric electrojet, seasonal movement of electrojet current focal latitude and width, and the electrodynamics effects of local winds.