Preliminary Analysis of Annual and Semi-Annual Variations of the Geomagnetic Field

Malin and Isikara (1976) proposed that the annual variation in the night-time values of the geomagnetic field was caused by an annual variation in the latitude of the ring current. Butcher and Schlapp (1992), using longer runs of data, showed that, besides the ring current component, there was also a smaller component of unknown origin. In this paper we model the ring current effect by considering the magnetic effect on a sphere inside a coil of finite length which moves up and down the axis with a period of one year. The latitude variation of the magnitude of the annual (and semi-annual) variation for this case is determined and compared with results obtained at a number of stations in order to find the maximum amplitude of the coil movement. Unfortunately this preliminary analysis was unsuccessful in determining the maximum amplitude of the coil movement.