Annual and semi-annual S^sub q^ variations at 96° MM MAGDAS I and II stations in Africa

The quiet daily variations of the geomagnetic field (S ^sub q^) have been studied by using the geomagnetic data of the 10 International Quietest Days. Geomagnetic data from MAGDAS I and II stations--ten stations were selected around the 96° magnetic meridian (MM)--over Africa have been analyzed from September 2008 to August 2009. The analysis of this unique data set clarifies the characteristics of the S ^sub q^ variations over the African sector for the first time by observational geomagnetic data. In this paper, we found that S ^sub q^(H) and S ^sub q^(D) show a predominantly annual variation. The most interesting result, and a new finding in the African sector, is the appearance of two vortices in the day lit southern hemisphere during spring. Further data analysis also revealed many other interesting characteristics for the S ^sub q^ over the African sector.