Publication

Secular change of the Earth's magnetic field is a comparatively regional phenomenon and does not proceed in a regular manner across the Earth. This gives rise to regions where the magnetic field changes more rapidly than elsewhere, like for instance southern Africa. As part of a cooperative project between Germany and South Africa, called Inkaba ye Africa, the COMPASS (Comprehensive Magnetic Processes under the African Southern Sub-continent) program aims to study the regional geomagnetic field and in particular its evolutionary behaviour. In addition to a rapid decrease of the geomagnetic field in this region, as evidenced by the 20% decrease observed at Hermanus, the orientation of the geomagnetic field in southern Africa is also changing rapidly. In the north-western part of southern Africa the declination of the magnetic field is propagating eastward (Tsumeb) and in the southeastern part it propagates westward (Hermanus and Hartebeesthoek). This results in an overall increase of the spatial gradient over the subcontinent with time. During 2005, 2006 and 2007 joint field survey campaigns were conducted by the Hermanus Magnetic Observatory (HMO) and the GeoForschungsZentrum Potsdam (GFZ) in South Africa, Namibia and Botswana in order to characterize the time variation of different components of the geomagnetic field. Results obtained from these field surveys, together with data from the 3 continuous recording magnetic observatories in southern Africa at Hermanus, Hartebeesthoek and Tsumeb, are used to model the geomagnetic field time variation for 2005-2008.

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Kotzé, P.; Mandea, M.; Korte, M. (2008): Modelling secular variation over southern Africa using 2005, 2006 and 2007 field survey data. 13th IAGA Workshop on Geomagnetic Observatory Instruments, Data Acquisition and Processing (Golden and Boulder, Colorado 2008).