Abstract
We describe the British Geological Survey’s 11th generation International Geomagnetic Reference Field candidate models. These models are based on a ‘parent model’ consisting of a degree and order 60 spherical harmonic expansion of selected vector and scalar magnetic field data from satellite and observatory sources within the period 1999.0 to 2010.0. The parent model’s internal field time dependence for degrees 1 to 13 is represented by linear spline with knots 400 days apart. The parent model’s degree 1 external field time dependence is described by periodic functions for the annual and semi-annual signals, and by dependence on the 20-minute Vector Magnetic Disturbance index. Signals induced by these external fields are also parameterised. Satellite data are weighted according to two noise estimators. Firstly by standard deviation along segments of the satellite track and secondly a larger-scale noise estimator defined in terms of a vector activity measure at the geographically closest magnetic observatories to the sample point.
Highlights
The International Geomagnetic Reference Field (IGRF)is a widely used model of the Earth’s main magnetic field and is produced every 5 years by a collaboration of modelling teams at the invitation of the International Association of Geomagnetism and Aeronomy (IAGA) Division V committee
In addition to the core and large scale lithospheric sources that are the focus of the IGRF-11 modelling effort, this large compilation of satellite and observatory data contain fields produced from
HAMILTON et al.: BGS MAGNETIC FIELD CANDIDATE MODELS FOR IGRF-11 and a larger scale estimator of the vector disturbance using observatories nearest to the data sample
Summary
The International Geomagnetic Reference Field (IGRF)is a widely used model of the Earth’s main magnetic field and is produced every 5 years by a collaboration of modelling teams at the invitation of the International Association of Geomagnetism and Aeronomy (IAGA) Division V committee. The production of our BGS candidate models was carried out in three steps: selection of data from Ørsted, CHAMP, and ground observatories; fitting and evaluating the parent model; and extraction of the IGRF-11 candidate MF and SV coefficients. Since the production of the BGS IGRF-10 candidate models (Lesur et al, 2005), the most significant changes to our parent model have been to include more detailed parametrisation of external sources and the use of vector data at all latitudes with appropriate noise estimation.
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