The World Magnetic Model (WMM) is a 12‑degree spherical‑harmonic representation of the Earth's main magnetic field, jointly produced by NOAA NCEI and the British Geological Survey and sponsored by the U.S. National Geospatial‑Intelligence Agency and the U.K. Defence Geographic Centre. The current version, WMM2025, was released on 17 December 2024 and is valid through 31 December 2029.
Development and Release
The WMM is updated at five‑year intervals to provide accurate geomagnetic data for military, aviation, maritime and civilian navigation systems. An out‑of‑cycle update was issued in 2019 to address rapid north‑pole drift【https://www.ncei.noaa.gov/news/world-magnetic-model-out-cycle-release】. The 2025 release introduced a high‑resolution companion, WMMHR2025, offering ~300 km equatorial resolution compared with the standard ~3300 km resolution【
https://www.ncei.noaa.gov/news/world-magnetic-model-2025-released】.
Technical Specifications
WMM2025 uses a degree and order 12 spherical‑harmonic series with 168 Gauss coefficients for the main field and corresponding secular‑variation coefficients. The high‑resolution model expands the core field to n = 15 and adds a crustal component up to n = 133, totaling 18 210 non‑zero coefficients and four‑digit precision【https://geomag.colorado.edu/wmm2025-and-wmmhr2025】.
Data Sources and Methodology
The model combines vector and scalar magnetic measurements from the ESA Swarm satellite constellation with data from about 160 ground observatories collected up to October 2024【https://geomag.bgs.ac.uk/research/modelling/WorldMagneticModel.html】. Independent candidate models from NOAA and BGS are averaged after cross‑validation to produce the final coefficients【
https://library.oarcloud.noaa.gov/noaa_documents.lib/NESDIS/NCEI/WWM_Report_2025.pdf】.
Usage and Sponsors
WMM provides the baseline for magnetic declination corrections in GPS‑enabled devices, aviation navigation, maritime charting (IHO), and military systems (DoD, UK MoD, NATO). It also underpins consumer electronics and scientific research. The model meets the accuracy requirements of MIL‑PRF‑89500B and includes updated blackout zones near the magnetic poles where magnetic heading is unreliable【https://www.nga.mil/assets/files/24-18_Release_WMM2025_FINAL.pdf】.