Earth's Second Magnetic Field: Satellite Image Reveals Invisible Force From Ocean Currents

The Earth has a second magnetic field, one generated by ocean currents. Researchers know little about it, but images captured by satellites show this invisible force generated by the world's salty oceans in perfect detail.

To gain more insight into the powerful force from ocean currents, the European Space Agency used Swarm -- three identical spacecraft launched in 2013. Swarm mapped the magnetic fields generated by ocean tides which continued to pique the curiosity of researchers. Images from the satellites were presented during the European Geosciences Union meeting in Vienna, Austria.

The Swarm is the perfect way to observe the oceans since it tracks the water column's movement straight down to the seabed. The Swarm helps researchers create better Earth models, and findings are crucial for climate studies.

Ocean Current Mapping

Based on the images provided by the Swarm, researchers created a 3D map and learned how the magnetic field behaves. What triggers the formation of the protective magnetic field with a cocoon-like quality and how it changes is also part of the study. ESA released a video detailing the changes in the Earth's magnetic field over a 24-hour period.

Technical University of Denmark head of geomagnetism Nils Olsen talked about the contribution of the ocean currents to the planet's magnetic field

"It's a really tiny magnetic field. It's about 2-2.5 nanotesla at satellite altitude, which is about 20,000 times weaker than the Earth's global magnetic field."
Oceans may have a small contribution to the magnetic field that protects the planet from harmful cosmic rays, but it remains to be an essential element. Seawater serves as an electric conductor. Aside from that, oceans move with the tide which could affect the magnetic field.

Olsen further explained the relevance of the findings from Swarm.

"In addition, because this tidal magnetic signal also induces a weak magnetic response deep under the seabed, these results will be used to learn more about the electrical properties of Earth's lithosphere and upper mantle."
The information used to create the map was taken from four years worth of data from Swarm measurements and Champ, a German spacecraft. Researchers also referenced data from ships and airplanes.

North Magnetic Pole Movement

ESA's Rube Floberghagen revealed to BBC why the study of the magnetic field is valuable.
"Magnetic fields are one of the keys to understand the sub-surface of the planet, in combination with other pieces of information such as gravity and seismic measurements."
Among the findings from the Swarm mission includes the position of the north magnetic pole.
The pole has been moving from Canada to the direction of Russia, and Swarm has been paying close attention to its shifting. Olsen explains, in 2018, the north magnetic pole will be closest to the geographic pole with a separation of only 390 km. The magnetic pole's movement is pegged at 55 km per year, he adds.

With the information provided by Swarm, researchers expect to create a better model of the Earth's main and secondary magnetic field and to understand all the factors involved including the influence of ocean currents.