Improved observations at the southern African geomagnetic repeat station network

Abstract

Within the Inkaba yeAfrica project, the number of geomagnetic repeat stations surveyed in southern Africa has been increased recently from eight to almost 40, through cooperation between Hermanus Magnetic Observatory (HMO), South Africa and GeoForschungsZentrum Potsdam (GFZ), Germany. Taking advantage of the extensive network of well-marked repeat stations formerly established by HMO in South Africa, Namibia and Botswana, and experience gained in using on-site variometers in former repeat station surveys carried out by GFZ, we could significantly improve the spatial data coverage of the area and also the quality of the results. Here we report on the survey and data processing methods, and discuss the accuracy of results, particularly with respect to the ability of the data to reflect the undisturbed internal magnetic field. Moreover, we briefly discuss how differences in the variometer recordings can reflect possible lateral changes in lithospheric conductivity.

Morphology of the southern African geomagnetic field derived from observatory and repeat station survey observations: 2005–2014

“…Vector field observations at each station are in general done in the evening and morning, with a three-component fluxgate variometer operating the whole time and during the night. Corrections for diurnal and other short-term external field variations are then made by reducing field station observations to nighttime average values (see Korte et al 2007 for details).…”

“…In southern Africa, encompassing South Africa, Namibia and Botswana, three geomagnetic observatories provide continuous data series for several decades and repeat surveys have been conducted on a routine basis for nearly 50 years. Since 2005, they have been executed on an annual basis and an additional observatory has been established in southern Namibia ), in order to better monitor the observed rapid geomagnetic field changes in this region ; Korte et al 2007). …”

The magnetic field changing over the southern African continent: a unique behaviour

“…During the last few decades, efforts have been taken by Hermanus Magnetic Observatory to establish and measure a network of repeat stations, today covering the territories of South Africa, Namibia and Botswana (Kotzé et al, 2007a). During the last two years these stations were reoccupied and measured on a yearly basis in the frame of the COMPASS project.…”

A harmonic spline magnetic main field model for Southern Africa combining ground and satellite data to describe the evolution of the South Atlantic Anomaly in this region between 2005 and 2010

“…These data were collected by running a LEMI-008 fluxgate vector magnetometer over night and taking absolute observations in the evening and morning using the standard absolute equipment of a DIfluxgate magnetometer (http://www.bartington.com/ mag-01h-declinometer-inclinometer-system.html) and an Overhauser magnetometer (http://www.gemsys.ca/ technology/ground/). The absolute observations provide baseline values for the variometer values, which are averaged over the night hours between 20:00 and 06:00 LT to obtain the main field values at this geomagnetic repeat station for this particular night when the survey is conducted (Korte et al 2007). The repeat stations thus provide approximately annually spaced values for quiet night times.…”