The European Space Agency (ESA) launched its trio of Earth-facing satellites – the Swarm satellites – more than two years ago. Since then, the three probes have been tirelessly making measurements of the Earth's magnetic field, mapping it out in detail. Now, that data has been used in a new study of how the magnetic field has changed over recent years, with the results echoing what's happening at the planet's core.

Earth's magnetic field might be invisible, but it's complex and ever-changing, protecting us from cosmic radiation and solar winds. Since launching at the tail end of 2013, ESA's Swarm satellites have been studying the different magnetic signals from the planet's core, mantle, crust, oceans, all the way out to the ionosphere and magnetosphere.

All that data was recently used in a study to describe where the magnetic field is getting weaker, where it's strengthening, and perhaps most importantly – how fast those changes are occurring. The findings are presented at the Living Planet Symposium, which is being held this week, and include two animations showing the changes.

The first animation, which also makes use of data from CHAMP and Ørsted satellites, shows changes in field strength between 1999 and May 2016. The red regions are where it got stronger, while the blue regions show a weakening.

Overall, the magnetic field has weakened by some 3.5 percent over North America, but has become around 2 percent stronger over Asia. The absolute weakest area of the field, known as the South Atlantic Anomaly, also weakened by some 2 percent as it moved steadily to the west.

The second animation is a little different, describing the rate of change between 2000 and 2015. Similar to the first animation, slowing regions are seen in blue, while those speeding up are visible in red. It's a complex picture, with changes increasing in speed over Asia, while they slow down around South Africa.

What's causing all of those changes? Well, the magnetic field is thought to be the result of the vast quantities of molten iron moving around some 3,000 km (1,860 miles) beneath the surface. The changes, it's thought, are caused by alterations in how the liquid is flowing.

"Swarm data are now enabling us to map detailed changes in Earth's magnetic field, not just at Earth's surface but also down at the edges of its source region in the core," said senior scientist Chris Finlay. "Unexpectedly, we are finding rapid localised field changes that seem to be a result of accelerations of liquid metal flowing within the core."

As they continue to move through their third year of taking measurements, the Swarm satellites will continue to study the magnetic field. In so doing, they will continue to provide valuable insights into how the field is changing, while helping us to improve our understanding of what drives those changes.

Source: ESA

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