The World Magnetic Model (WMM) is an important model of Earth’s magnetic field produced jointly by the United States’ National Centers for Environmental Information (NCEI) and the British Geological Survey (BGS).
The WMM has several important applications:
- Navigation – It provides declination values to convert between true north and magnetic north on maps and navigation systems used at sea, in the air, and on land.
- Heading – The WMM data allows calibrating heading indicators for ships, aircrafts, land vehicles by accounting for local inclination and declination.
- Mapping – Magnetic charts use the model’s declination, inclination and intensity grids to create accurate magnetic representations.
- Smartphone compass apps – The declination data from the WMM is built into compass apps to correct between true and magnetic north.
- Surveying and tracking sea ice – Declination values enable magnetic north corrections for surveying and studying polar ice movements.
- Satellite orientation – The model helps orient satellites relative to Earth’s local magnetic fields.
- Studying Earth’s core and crust – The WMM provides insights into the magnetic properties of the core and crust.
The WMM models the magnetic field generated by both Earth’s core as well as magnetized crustal rocks. It is represented as a series of spherical harmonic equations. The model provides global gridded values for magnetic declination, inclination and intensity. It is updated every 5 years, with the latest WMM2020 released in December 2019 and WMM2025 expected in 2024.
The WMM is created by combining data from diverse sources:
- Satellite, ground observatory, airborne, and marine magnetic field measurements provide global coverage.
- Historically repeated observations and archaeomagnetic data assist in modeling field changes.
- Expert geomagnetic modelers from NCEI and BGS process the data through spherical harmonic equations, optimizing to minimize deviations.
- Frequent updates account for new data and the continuously evolving field.
In summary, the globally collaborative World Magnetic Model plays a critical role in navigation, orientation, and studying Earth’s magnetic field and its sources. Regular updates and new data incorporation keep it an accurate representation of this key physical phenomenon.
