The secular variation and secular acceleration of the Earth’s geomagnetic core field pose a difficult challenge for field modellers, and particularly for forecasting future evolution of the field. Models must describe the scope of spatial and temporal changes, which are often poorly resolved and masked by variations of other field sources, and parameterise the observed signals accordingly. In retrospect, variations can be accurately modelled using observations from the global network of ground observatories and satellites, but for practical applications, field models are used to predict the future state of the field.
Models such as the International Geomagnetic Reference Field and World Magnetic Model are produced on a quinquennial basis, and predict the core field for the subsequent 5 years. These models are widely used in academia, industry and by governmental and international organisations for purposes such as navigation, mineral exploration and space physics. Given our incomplete understanding of the physical state of the outer core however, such predictive models are often based on simple extrapolations.
We quantify the error from regular extrapolations in a range of core field models, in order to negate the effects of data availability and those arising near model ends. We investigate the presence and predictability of temporal and spatial trends in these errors. Our tests confirm the impact of jerks and high latitude effects, and also suggest predictions are less reliable over the South Atlantic Anomaly. We note that global prediction errors are correlated with external field sources temporally
