Not all who wander are lost – updating the International Geomagnetic Reference Field

The Earth’s magnetic field is not static and varies on many different time scales. The main source of the long-term field variation comes from the outer core where the magnetic field is generated by the motion of liquid nickel-iron which in turn ‘drags’ the field lines with it. Thus, the field changes strength and shape slowly over decades. Every five years, IAGA issues an updated version of the magnetic field to capture these slow changes known as secular variation. This series of ‘maps’ or models are known as the International Geomagnetic Reference Field (IGRF) and goes back 125 years. In November 2024, the 14th generation of the model was released, valid from January 1900 to December 2030.

Figure 1: Strength of the magnetic field in microTelsa on the Earth’s surface at 2025.0. Note the low strength region known as the South Atlantic Anomaly.

The magnetic field is represented by a series of numbers known as Gauss coefficients. Using the mathematical technique of spherical harmonic analysis, the magnetic field can be represented continuously in time and space rather than as a 3D grid of cells. This means we can provide a snapshot of the magnetic field above, at or below the Earth’s surface using a very compact set of just 195 numbers, which gives an approximate resolution of 3000 km. This captures the vast majority of the core field and allows us to calculate of Declination angle, Magnetic Dip and Total Field Intensity (see Figure 1) anywhere in the world. We can also track the location of the magnetic poles (see Figure 2).

The first IGRF for 1965 was issued in 1968 when it was difficult to get timely datasets of magnetic measurements from observatories – the data usually took several years to produce and was distributed by post! When the modern internet era began in the 1990s, data could be circulated more rapidly and the IGRF began to be produced in a more timely fashion. Today, we live in a golden era of magnetic field measurement: from hundreds of high-quality geomagnetic observatories to dedicated magnetic missions such as ESA Swarm and Macau Science Satellite. Together these freely available, near-real-time datasets and cheap powerful computer make core field modelling widely accessible.

Figure 2: Estimated location of the geomagnetic and magnetic dip poles from 1900 to 2030. While the north dip pole has accelerated over the past 20 years moving from Canada toward Siberia, the south dip pole has moved much more slowly.

For the 14th generation, 19 teams of geomagnetic scientists from four continents submitted candidate models for the magnetic field in 2020 and 2025 and a forecast of secular variation between 2025 and 2030. In total, there were 47 candidate models to evaluate. The method for combination was determined by a panel of experts using a variety of different technical analyses. The final models were agreed by majority vote and the new coefficients were issued to the official IAGA website on 20th November 2024.

The IGRF is used for research for deep Earth and space weather forecasting, part of many industry applications for correcting surveys (archaeology, oil/gas, mineral exploration) as well as standard pointing and navigation uses. The IGRF truly is an international effort involving thousands of observers, scientists and engineers from around the world. Without their contributions, this would not be possible. We thank them all for their work.

Authors: Ciaran Beggan is senior researcher at British Geological Survey in Edinburgh. This is his fourth venture with the IGRF, starting as a PhD student back in 2009. Clemens Kloss is a postdoctoral researcher at DTU Space in Copenhagen who specialises in improving our view of the Earth’s core magnetic field minus the annoying effects of the aurora.