Time variations of the geomagnetic field can be classified into two main categories of internal and external origin with respect to the surface of the Earth. It has been found that the variations that take place on longer time scales are commonly known as secular variation and are of internal origin. The authors study the time variations of the geomagnetic field on longer time scales over southern Africa region applying two regional geomagnetic field modelling techniques, namely, Polynomial Surface Modelling and Spherical Cap Harmonic Analysis to CHAMP satellite observations recorded between...
Time variations of the geomagnetic field can be classified into two main categories of internal and external origin with respect to the surface of the...