International audienceThe eleventh generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2009 by the International Association of Geomagnetism and Aeronomy Working Group V-MOD. It updates the previous IGRF generation with a definitive main field model for epoch 2005.0, a main field model for epoch 2010.0, and a linear predictive secular variation model for 2010.0–2015.0. In this note the equations defining the IGRF model are provided along with the spherical harmonic coefficients for the eleventh generation. Maps of the magnetic declination, inclination and total intensity for epoch 2010.0 and their predicted rates of change for 2010.0–2015.0 are presented. The recent evolution of the South Atlantic Anomaly and magnetic pole positions are also examined

Abstract.Magnetic measurements taken by the Orsted satellite during geomagnetic quiet conditions around January 1, 2000 have been used to derive a spherical harmonic model of the Earth's magnetic field for epoch 2000.0. The maximum degree and order of the model is 19 for internal, and 2 for external, source fields; however, coefficients above degree 14 may not be robust. Such a detailed model exists for only one previous epoch, 1980. Achieved rms misfit is < 2 nT for the scalar intensity and < 3 nT for one of the vector components perpendicular to the magnetic field. For scientific purposes related to the Orsted mission, this model supercedes IGRF 2000.

S U M M A R YThe International Association of Geomagnetism and Aeronomy (IAGA) on 2004 December 12 has released the 10th-Generation International Geomagnetic Reference Field-the latest version of a standard mathematical description of the Earth's main magnetic field used widely in studies of the Earth's deep interior, its crust, ionosphere and magnetosphere. The coefficients were finalized by a task force of IAGA. The IGRF is the product of a large collaborative effort between magnetic field modellers and the institutes involved in collecting and disseminating magnetic field data from satellites and observatories around the world.

Definitive internal geomagnetic field models are derived for the epochs 1945, 1950, 1955, and 1960. Each model incorporates all data available to us within a five year period centered on the model epoch. For survey data, weighting was determined by examining the spread of residuals for the data, sorted by source and sorted by location, relative to the previous IGRF models. The solution included local biases for the fixed observatories. An a priori model for each epoch was derived by projecting the GSFC (12/83) model, based on Magsat data, backward in time. This projection was accomplished using a spline fit to annual secular-variation models. The spline coefficients were simultaneously fit to all spherical harmonic secular variation coefficients for the 1940 to 1980 time period. This fit included a full covariance analysis. The projected covariances were part of the a priori model for each epoch. An uncertainty model was adopted which included estimates of the effects of crustal and core fields not represented by the model. Differences between model coefficients midway in time between model epochs were compared to estimated coefficient uncertainties. Coefficient differences were within the estimated uncertainties, confirming the uncertainty model. A test for 1945 indicated that a solution without observatory biases was equal to that with such biases, within the expected uncertainties. Differences between biases from year to year are within the bounds expected based on the predicted uncertainties. The resulting models, their secular variation and their expected uncertainties are discussed in some detail.

S U M M A R YThe International Association of Geomagnetism and Aeronomy (IAGA) on 2004 December 12 has released the 10th-Generation International Geomagnetic Reference Field-the latest version of a standard mathematical description of the Earth's main magnetic field used widely in studies of the Earth's deep interior, its crust, ionosphere and magnetosphere. The coefficients were finalized by a task force of IAGA. The IGRF is the product of a large collaborative effort between magnetic field modellers and the institutes involved in collecting and disseminating magnetic field data from satellites and observatories around the world.The IGRF is a series of mathematical models of the Earth's main field and its annual rate of change (secular variation). In source-free regions at the Earth's surface and above, the main field, with sources internal to the Earth, can be represented as the negative gradient of a scalar potential V , expanded into spherical harmonics as V (r, θ, λ, t) = R nmax n=1 R r n+1 n m=0 g m n (t) cos mλ + h m n (t) sin mλ P m n (θ ), where r , θ, λ are geocentric coordinates (r is the distance from the centre of the Earth, θ is the colatitude, i.e. 90 • − latitude, and λ is the longitude), R is the magnetic reference radius (6371.2 km); g m n (t) and h m n (t) are the coefficients at time t, and P m n (θ ) are the Schmidt semi-normalized associated Legendre functions of degree n and order m. The main-field coefficients are functions of time. For the IGRF the change is assumed to be linear over 5-year intervals. For the upcoming 5-year epoch, the rate of change is given by predictive secular variation coefficientsġ m n andḣ m n . For more details on mainfield modelling the reader is referred to Chapman & Bartels (1940) and Langel (1987).The coefficients of the 10th-generation IGRF are listed in Table 1 and are available in digital form from the IAGA web site www.iugg.org/IAGA and the World Data Centers listed at the end of this paper, along with software to compute magnetic field values from them. The new coefficients are the preliminary main-field coefficients for 2005.0 and the predictive secular-variation coefficients for 2005.0-2010.0. The previous (9th) generation IGRF with the definitive coefficients for 1995.0 and 2000.0 (Macmillan et al.