Abstract
Global geomagnetic field models using spherical harmonic basis functions are important in space physics research, space weather and applications like navigation and mineral resources exploration. These models are based on various geomagnetic field data sets ranging from Earth surface magnetic observatory measurements to low-Earth orbit satellites equipped with highly sensitive and accurate magnetometers. Although these field models are derived by fitting harmonic functions to data distributed across the Earth, they are applied on regional scales within fixed boundaries in many instances and one can therefore question how well do these models perform on restricted areas. Three recently published global geomagnetic field models, IGRF-12, CHAOS-6 and POMME-10, have been statistically evaluated over Southern Africa using repeat station data as well as measurements from 4 INTERMAGNET observatories located at Hermanus and Hartebeesthoek in South Africa as well as Tsumeb and Keetmanshoop in Namibia for 2015. Apart from the observatory data, the field survey repeat station data do not form part of the data set on which these global field models are based and therefore can be regarded as an independent test of these field models over an area like Southern Africa which is well known for its rapid change of the geomagnetic field. Results obtained in this investigation for both main field and secular variation models clearly showed the importance of timely ground-based geomagnetic field observations in the derivation of accurate field models, particularly in regions characterised by rapid and unpredictable secular variation changes.
Highlights
The Earth’s magnetic field, originating predominantly in the liquid outer core through a self-sustaining dynamo action, has been observed in a systematic way since the middle of the nineteenth century at various positions around the globe
Global geomagnetic field models like International Geomagnetic Reference Field (IGRF)-12, CHAOS-6 and POMME-10 are important tools utilised by researchers and commercial users to obtain various characteristic parameters of the Earth’s magnetic field as a function of time and geographic position
All 3 models used in this study describe main field D and H, Z and F well
Summary
The Earth’s magnetic field, originating predominantly in the liquid outer core through a self-sustaining dynamo action, has been observed in a systematic way since the middle of the nineteenth century at various positions around the globe. *Correspondence: pkotze@sansa.org.za South African National Space Agency (SANSA), Space Science, Hermanus, South Africa geomagnetic field models, IGRF-12 (Thébault et al 2015), CHAOS-6 (Finlay et al 2016) and POMME-10 (www.geomag.org/models/pomme10.html), using various combinations of observatory and satellite data, were published to describe the Earth’s magnetic field and its time variation.
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