摘要
This study examines the prenoon-postnoon asymmetrical behaviour and latitudinal dependence of Sq （solar quiet） current system using data of quiet-time daily variations of the geomagnetic field intensity from twelve geomagnetic observatories along the African Meridian. The dataset of each month during 2009 （noted for empirically low solar activity with average sunspot number Rz = 3.1） was treated for non-cyclic correction. From a blend of spatial contour maps and graphical analyses, our results show that Sq current system exhibits in the daytime unstable tendency. A consistent diurnal variation of solar quiet variation in the horizontal component of earth magnetic field （SqH） was observed which exhibits synoptic pre-noon and post-noon mean values of 59 nT and 33 nT with ranges of 33 nT and 24 nT, respectively. The centre of circulation of overhead electric current is observed to exhibit both pre-noon and post-noon epoch＇s asymmetric variations. This is noted to indicate the dynamic heterogeneous genesis of the mechanism responsible for the observation. The spatial contour mapping result depicts SqH behaviour switch twice a year around March and September with similar spatial distribution in January up to March and then October up to December. A similar distribution was noted for the months of April to September. Prenoon values of SqH have higher magnitudes across the latitudes in comparison with the post noon values just as is the case at noontime.
