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| International Geomagnetic Reference Field | |
|---|---|
| Name | International Geomagnetic Reference Field |
| Caption | Model grid representation |
| Established | 1965 |
| Maintained by | International Association of Geomagnetism and Aeronomy |
| Domain | Geomagnetism |
International Geomagnetic Reference Field is a standardized spherical harmonic model representing the main part of the Earth's geomagnetic field used for navigation, research, and geophysical applications. Developed and maintained by the International Association of Geomagnetism and Aeronomy and its working groups, the model provides a compact description of the field through coefficients updated periodically to reflect secular variation observed by observatories, satellites, and surveys. It underpins operational systems in agencies such as the National Aeronautics and Space Administration, the European Space Agency, and the National Oceanic and Atmospheric Administration.
The model expresses the Earth's main magnetic field as a set of Gauss coefficients in a spherical harmonic expansion, offering a baseline for declination, inclination, and intensity used by United States Navy navigation, Royal Canadian Navy operations, and aviation authorities like the International Civil Aviation Organization. It separates internal field sources associated with the Earth's core from external contributions tied to magnetospheric and ionospheric currents monitored by missions such as Swarm (ESA mission) and Ørsted (satellite). Users from institutions like the United States Geological Survey, the British Geological Survey, and the Geological Survey of Canada apply the model for geomagnetic surveys, mineral exploration, and geodynamo studies referencing work by researchers at Scripps Institution of Oceanography and Institut de Physique du Globe de Paris.
The initiative originated in the 1960s through collaborative efforts among the International Union of Geodesy and Geophysics and early geomagnetic observatory networks including Greenwich Observatory and German Research Centre for Geosciences. Early versions succeeded regional and national charts used by the Royal Navy and the United States Coast and Geodetic Survey. Revisions incorporated data from landmark campaigns and satellite programs such as Magsat and Pioneer 11 as techniques advanced in institutions like Massachusetts Institute of Technology and California Institute of Technology. Working groups from the International Association of Geomagnetism and Aeronomy coordinated methodological standards with contributions from observatories at Eskdalemuir Observatory, Station de Géomagnétisme de Chambon-la-Forêt, and the College of William & Mary research teams.
The model is parameterized by Gauss coefficients (g_n^m, h_n^m) up to a specified spherical harmonic degree and order, following formalisms developed in texts from Cambridge University Press authors and methodologies used at National Center for Atmospheric Research. The main field component models contributions from the outer core geodynamo while secular variation is expressed as time derivatives of coefficients comparable to techniques in studies at University of Cambridge and ETH Zurich. Crustal anomalies and lithospheric signals appear at higher harmonic degrees similarly explored by researchers at University of Oxford and University of Tokyo, whereas external field corrections reference magnetospheric models developed at Los Alamos National Laboratory and Akasofu Institute.
Calibration relies on long-term observatory series from networks including the INTERMAGNET consortium and satellite datasets from missions such as CHAMP (satellite), Swarm (ESA mission), and Magsat. Aeromagnetic and marine survey contributions come from projects run by agencies like the United States Geological Survey and the Geological Survey of Canada, with processing techniques aligned with standards from International Organization for Standardization committees and analysis methods used at National Institutes of Natural Sciences (Japan). Data selection, screening, and weighting procedures reflect practices established in studies at Leibniz Institute of Atmospheric Physics and the Max Planck Institute for Solar System Research.
Operational uses include navigation for maritime services overseen by the International Maritime Organization and aviation procedures coordinated by the International Civil Aviation Organization, as well as compass correction tables produced by navies such as the Royal Australian Navy. Scientific applications span geodynamo research at Princeton University, plate tectonics and paleomagnetism studies at University of California, Berkeley, and space weather forecasting at NOAA Space Weather Prediction Center. The model supports instrument calibration in laboratories at National Physical Laboratory (UK) and mission planning for planetary missions from Jet Propulsion Laboratory.
The model represents the large-scale internal field but omits fine-scale lithospheric features beyond its harmonic truncation, a constraint addressed in regional models developed at University of Southamption and Curtin University. External field contamination during geomagnetic storms driven by events like the Carrington Event and solar activity recorded by Solar and Heliospheric Observatory can introduce errors; mitigation strategies draw on analyses from European Space Agency mission teams and the Space Weather Prediction Center. Uncertainties arise from temporal sparsity in observatory coverage in regions such as the Southern Ocean and polar gaps influenced by logistics coordinated with British Antarctic Survey and Australian Antarctic Division.
New coefficient sets are released approximately every five years by the working group within the International Association of Geomagnetism and Aeronomy, with interim secular variation models and candidate updates reviewed at conferences such as the General Assembly of the International Union of Geodesy and Geophysics and workshops hosted by centers like World Data Center for Geomagnetism, Kyoto. Versioning and distribution involve collaborations with agencies including European Centre for Medium-Range Weather Forecasts and National Centers for Environmental Information, and rely on community validation by observatories in the INTERMAGNET network and academic groups at University of Leeds and University of Oslo.
Category:Geomagnetism