Measuring the Ocean’s Magnetic Field with Satellites

The European Space Agency (ESA) has for the first time measured faint magnetic signals generated by the ocean, revealing new details of the electrical phenomena of the inner Earth.

The Earth is shielded from cosmic radiation by magnetic fields, protecting the atmosphere and enabling life as we know it to exist. They originate from different parts of the Earth, at different strengths, the reasons for which are not clearly understood. These fields are gradually weakening, and more knowledge is needed to understand why.

The ESA’s swarm satellites were launched in 2013 for precisely this purpose. Roger Haagnans, ESA Swarm Mission Scientist said “Its astonishing the team has been able to use just two years worth of measurements from Swarm to determine the magnetic field effect from the ocean and to see how the conductivity changes in the lithosphere and upper mantle. Their work shows that down to about 350 km below the surface, the degree to which material conducts electric currents is related to composition. In addition, their analysis shows clear dependence on tectonic settling of the ocean plate. In the future we may get a full 3d view of conductivity below the ocean.”

The different sources that contribute to the magnetic field measured by Swarm. The coupling currents or field-aligned currents flow along magnetic field lines between the magnetosphere and ionosphere. Source: ESA/DTU Space

The different sources that contribute to the magnetic field measured by Swarm. The coupling currents or field-aligned currents flow along magnetic field lines between the magnetosphere and ionosphere. Source: ESA/DTU Space

They found that ocean tides generates an electric field as the salty water flows through the Earth’s magnetic field. This in turn induces a magnetic field in the Earth’s crust. Alexander Gragher from ETH Zurich said “The Swarm and satellites have allowed us to distinguish between the rigid ocean ‘lithosphere’ and the more pliable ‘asthenosphere’ underneath.

These findings are important for a deeper understanding of plate tectonics.

Rune FlourGhafer, the ESA Swarm mission manager said “we have very few ways of probing deep into the structure of our planet, but Swarm is making extremely valuable contributions to understanding Earth’s interior, which then adds to our knowledge of how Earth works as a whole system.”

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