International Geomagnetic Reference Field

The International Geomagnetic Reference Field (IGRF) is a standard mathematical description of the Earth's main magnetic field and its secular variation. It is the product of a collaborative effort between magnetic field modellers and the institutes involved in collecting and disseminating magnetic field data from satellites and from observatories and surveys around the world.

Spherical Harmonics

Mathematically, the IGRF model consists of the Gauss coefficients which define a spherical harmonic expansion of the magnetic scalar potential.


  V(r,\phi,\theta) = a \sum_{\ell=1}^L\sum_{m=0}^\ell
  \left(\frac{a}{r}\right)^{\ell+1} \left(g_\ell^m\cos m\phi + h_\ell^m\sin m\phi\right) P_\ell^m\left(\cos\theta\right)

where r is radial distance from the Earth's center, L is the maximum degree of the expansion, \phi is East longitude, \theta is colatitude (the polar angle), a is the Earth's radius, g_\ell^m and h_\ell^m are Gauss coefficients, and P_\ell^m\left(\cos\theta\right) are the Schmidt normalized associated Legendre functions of degree l and order m.

IGRF models are standardized for a particular year, reflecting the most accurate measurements available at that time, and indicating a small-scale, slow time variation of the Earth's overall magnetic field.

See also

External links

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