Long-term monitoring of the Earth’s magnetic field

Hartland observatory from the air, showing a number of instrument houses surrounded by farmland.

The British Geological Survey monitors magnetic field variations in the UK — every second — at observatories in Lerwick (Shetland), Eskdalemuir (Scottish Borders) and Hartland (Devon).

We also operate observatories overseas on Ascension Island, Sable Island, in Alaska and at Port Stanley in the Falkland Islands, in association with local partners.

We use magnetometers to measure both the strength and direction of the magnetic field. Each field measurement is the sum of contributions originating in the Earth's core, mantle, crust ionosphere and magnetosphere. The core field is dominant but other contributions can be significant, depending on location on the Earth and whether the Sun is active (which we can tell if, for example, there are many sunspots).

Why do we monitor it?

A fluxgate magnetometer instrument in use at our observatories, with three orthogonal sensors encased in a non-magnetic marble block

Long-term monitoring and measurement of the Earth’s magnetic field helps to improve our scientific understanding of changes happening deep within the Earth.

Our data can help to:

  • Understand, map and model the (tens of kilometres per year) flow of the iron-rich liquid of the outer core of the Earth.
  • Understand details of geophysically important events, such as reversals in magnetic polarity, that occur over decades to millennia, where clearly we need to be prepared to continue to measure over the very long term!

Long-term monitoring also enhances our scientific understanding of Earth's space environment, which contains magnetic fields, electrical currents and radiation belts.

Magnetic monitoring also helps to improve:

  • Understanding of the solar influences on the Earth, including solar impacts on the atmosphere, e.g. in temperature and composition.
  • Understanding of the extremes in solar activity. Just how much of a risk does the Sun pose to modern technology, in space and on the ground? What can we learn about past solar activity from our archives?

How long have we been monitoring?

Monitoring has been continuous in the UK (under various government-funded bodies) for over 160 years, with occasional measurments going back to around the 1600s.

BGS magnetic data are invaluable, not only as a simple historical scientific record, but also because there are only a few continuous records anywhere in the world that began before the 20th century. BGS therefore maintains a rare resource for studying longer term changes in our natural environment.

For example, the ‘Carrington Flare' event in September 1859, is one of our magnetic records that is particularly sought after.

Paper magnetogram recorded at Kew during the ‘Carrington Flare’ event in September 1859

Further Information

Contact Alan Thomson for more information about BGS Geomagnetism.