Earth’s magnetic field: Fluctuations reveal waves inside the planet’s core

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Fluctuations in Earth’s magnetic field that repeat every seven years can be used to probe the inner workings of our planet

Earth

21 March 2022

By Chen Ly

Wave-like flow at the surface of the Earth's outer core and background magnetic field lines. — Diagram showing wave-like flow at the surface of Earth’s outer core and background magnetic field lines

Felix Gerick

Small magnetic waves discovered in Earth’s core could help illuminate what is going on deep inside our planet.

Earth’s core has a solid inner layer and an outer layer made of liquid metal. The difference in temperature between the hot centre and cooler exterior layer drives convection currents in the liquid, and the movement of charged particles in the metal creates the planet’s magnetic field.

The motion is turbulent and chaotic, and therefore the magnetic field varies over time. Nicolas Gillet at Grenoble Alpes University and his colleagues observed Earth’s geomagnetic field between 1999 and 2021 using data from satellites as well as observatories on the ground.

The team discovered that the magnetic field around the equatorial region of the core regularly fluctuated. These fluctuations repeated every seven years, drifting westward around the equator at speeds of around 1500 kilometres per year.

“What is important to know is that the magnetic field in the core evolves on very long timescales,” says Gillet. “And what we witnessed is only tiny wiggles on top of this.”

Although they are relatively small, studying these waves can help to improve our understanding of Earth’s inner workings.

There has been debate as to whether there is a thin layer of rock sitting between the outer core and the mantle above it that may explain changes in the magnetic field, says Gillet, but these findings suggest that there is no need for this layer.

The team also believes it is possible to image the geomagnetic field deep in the core using the newly discovered waves as well as to predict the future evolution of the field.

“It’s fascinating that by recording the magnetic field of the Earth using satellites, we’re able to image what’s going on more than 3000 metres below our feet,” says Gillet.

“This study is an exciting advance in our understanding of how Earth’s magnetic field operates on timescales of less than a decade,” says Chris Finlay at the Technical University of Denmark. “Much longer time series, requiring continuous observations of the geomagnetic field from space in the upcoming decades, are essential in order to fully test this new model and to enable their potential for probing the deep Earth to be realised.”

Journal reference: PNAS, DOI: 10.1073/pnas.2115258119