Core field changes from eleven years of Swarm satellite observations

The Swarm satellite trio has provided global vector magnetic field measurements, with high precision and absolute accuracy, for the past eleven years. Based on this consistent, high quality, dataset we describe here how Earth’s main (core-generated) magnetic field has evolved between 2014.0 and 2025.0. At the Earth’s surface, we find that the region in the South Atlantic where the field strength is weakest (below 26,000 nT), has expanded by 0.9% of Earth’s surface area and that the minimum intensity has decreased by 336 nT from 22,430 nT to 22,094 nT. In the northern polar region, we find that in Canada the area of strong field (above 57,000 nT) has diminished, decreasing in size by 0.65% of Earth’s surface area and with the maximum field strength decreasing by 801 nT from 58,832 nT to 58,031 nT. In contrast the corresponding strong field region in Siberia has grown in size, increasing in area by 0.42% of Earth’s surface area, with the maximum field intensity increasing by 260 nT from 61,359 nT to 61,619 nT. At the core-mantle boundary, reversed flux features under southern Africa have moved westward, converging towards reversed flux features that have surprisingly moved eastwards under mid-Atlantic, albeit further to the south. In the northern polar region a strong flux feature under the Bering strait has moved westwards along the inner-core tangent cylinder. At low latitudes, under Indonesia and the western Pacific, field features have moved eastwards. Field accelerations, including oscillations, are found to be most intense at low latitudes. The Swarm mission has for the past decade been an essential source of global information on the changes taking place in Earth’s main magnetic field. Due to the long timescales of the underlying core processes, extending the mission lifetime for as long as possible, in particular for the higher satellite Swarm Bravo, is expected to yield further scientific insights. A long mission for Swarm Bravo would be an efficient means of ensuring that the present era of high quality geomagnetic observations from space continues as new missions come online. • The Swarm satellite mission provides a high precision, absolute accuracy, global record of Earth’s magnetic field that now spans more than 11 years. • The weak magnetic field region in the South Atlantic, where the field is below 26,000 nT has expanded by 0.9% of Earth’s surface area between 2014.0 and 2025.0, with the field weakening most significantly south-west of Africa. • The strong field region in Canada, with intensity above 57,000 nT, has decreased in size by 0.65% of Earth’s surface area between 2014.0 and 2025.0; the corresponding strong field region in Siberia has increased in size by 0.42%. • These changes are produced by the evolution of the large-scale part of the core-mantle boundary field, with spherical harmonic degree lees than 6.