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International Geomagnetic Reference Field (IGRF)

In October 2019 BGS contributed to the creation of the 13th generation of the International Geomagnetic Reference Field (IGRF). The IGRF is a collaborative model produced by geomagnetists from around the world and endorsed by the International Association of Geomagnetism and Aeronomy (IAGA). The IGRF is a common tool of survey geophysicists and space scientists as a good quality reference model. The IGRF dates back to around 1970 and grew out of discussions that took place within IAGA in the 1960s following the World Magnetic Survey and International Geophysical Year of 1957-1958.

IGRF-13 online calculator

The IGRF is updated every five years, and currently describes the the field from 1900 to 2025. Currently the IGRF is a spherical harmonic degree 13 model, with maximum harmonic degree 8 for the SV component. Prior to 1995 the IGRF only extends to harmonic degree 10, because of the less dense data distribution, mainly ground observatories, that was typical of the pre-Ørsted, CHAMP, and (ongoing) Swarm satellite era. The models up to and including 2015 are now designated as ‘definitive’ models (i.e. known as DGRFs), in that the potential for further improving these is regarded by IAGA as slight.

 

The BGS candidate models for IGRF-13 were evaluated alongside those from fourteen other contributing teams, made up of institutes from nine nations (China, Denmark, France, Germany, Japan, Russia, Spain, UK, USA). In December 2019, the three BGS candidates for the 2015 definitive field, 2020 predicted field and 2020-2025 rate-of-change (secular variation, SV) models were accepted and incorporated into IGRF-13.

 

As well as describing maps of field components, as shown below, models such as the IGRF also provide information about the locations of the magnetic poles.

 

Declination from IGRF-13 for 2020.0
Map of predicted annual rate of change of declination from IGRF-13 for 2020.0-2025.0
Inclination from IGRF-13 for 2020.0
Map of predicted annual rate of change of inclination from IGRF-13 for 2020.0-2025.0
Horizontal Intensity from IGRF-13 for 2020.0
Map of predicted annual rate of change of Horizontal Intensity from IGRF-13 for 2020.0-2025.0
Vertical Intensity from IGRF-13 for 2020.0
Map of predicted annual rate of change of Vertical Intensity from IGRF-13 for 2020.0-2025.0
Total Intensity from IGRF-13 for 2020.0
Map of predicted annual rate of change of total intensity from IGRF-13 for 2020.0-2025.0