Illustration: ESA

The contribution of oceans to the Earth's magnetic field

Thursday 03 May 18

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Nils Olsen
Professor -head of Geomagnetism
DTU Space
+45 45 25 97 08

Contact

Chris Finlay
Professor
DTU Space
+45 45 25 97 13

Swarm mission

The Swarm mission consists of three identical satellites launched by ESA in 2013. They are orbiting 300-530 kilometres above the Earth and have now been measuring the Earth’s magnetic field continuously for more than four years.

DTU Space heads the scientific analysis of the measurements from the Swarm satellites, which are expected to be in operation and function for another 10-15 years. In addition, one of the principal instruments—a vector magnetometer—which is direction determined by means of star trackers—has been developed at DTU Space.

The mission has also produced a number of other scientific results. For example, researchers have used Swarm data to detect the motion of liquid metal within the core and to understand why GPS signals disappear periodically in an area near the Equator where the Earth’s magnetic field is very weak.
Researchers from DTU reveal new surprising details about the contribution of the oceans to the Earth’s magnetic field.

DTU Space caused a stir among the approximately 14,000 participants at the recent General Assembly of the European Geosciences Union (EGU) held in Vienna in April. Here, Professor Nils Olsen and his colleagues could, in fact, reveal new surprising details about the contribution of the oceans to the Earth’s magnetic field.

The researchers have determined how much the salty water in the oceans of the world contributes to the Earth’s magnetic field. The contribution has been calculated using data from ESA’s three Swarm satellites.

“We’ve used the Swarm satellites to measure the magnetic signals which are emitted by electric currents in the sea as a result of tidal movements,” says Nils Olsen, who conducts research into the Earth’s magnetic field and has a leading role in DTU’s scientific work with the Swarm mission.

“These measurements give us a global picture of how the oceans of the world move at all depths, and this is new.”

Important contribution to magnetic field
When salt water moves as a result of sea currents and tidal forces, this causes a movement through the Earth’s magnetic field. This generates a electric current, the weak magnetic signal of which contributes to the Earth’s overall magnetic field.

The contribution of the oceans is very small and varies depending on the temperature and salt content of the water. It has a strength of around 2-2.5 nanoteslas—when measured from satellites—whereas the Earth’s overall magnetic field is around 20,000 times more powerful.

“But it is of importance. For example in relation to being able better to determine electric conductivity beneath the oceans,” says Nils Olsen.

May increase the understanding of the circulation in the oceans
In addition to determining the electric properties of the Earth’s lithosphere and upper mantle, the new knowledge may possibly also be used to achieve a better understanding of the global circulation of the oceans.

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