Geomagnetic Jerk: Anomaly In Earth's Magnetic Field Explained

In the late 1970s, it was found that the Earth’s magnetic field experiences unpredictable, rapid and intense anomalies called geomagnetic jerks. But it has been a mystery among scientists how this phenomenon works – until today.

The geomagnetic jerk was initially described in 1978. It is an unpredictable event that easily accelerates the evolution of the planet’s magnetic field and affects the prediction of its activities. The magnetic field of the Earth is important, affecting various activities ranging from the GPS in our smartphones to the flight of low-altitude satellites. For these reasons, it is essential to accurately predict its evolution.

A researcher from Centre National de la Recherche Scientifique (CNRS) at Paris, France, and a colleague from the National Space Institute, Technical University of Denmark, were able to create a computer model to explain the geomagnetic jerk. Their paper was published in the journal of Nature Geoscience on April 22.

The Earth’s magnetic field is a result of the interaction of the energy and movement of the planet’s metallic core. There are two types of movement. First is the slow convection movement – can be measured in the scale of a century, and the second is the “rapid” hydromagnetic waves – can be detected in the scale of few years.

The researchers suspected that hydromagnetic waves are responsible for the jerks. However, the interaction of these waves with the movement of slow convection, along with other resulting factors, had yet to be revealed.

To answer this problem, researchers developed a computer simulation very close to the physical conditions of the Earth's core. The simulation required the equivalent of 4 million hours of calculation and was carried out thanks to the supercomputers of GENCI.

“Here we show that these signatures can be reproduced in numerical simulations of the geodynamo that realistically account for the interaction between slowcore convection and rapid hydromagnetic waves,” Julien Aubert and Christopher C. Finlay, researchers from CNRS and National Space Institute, respectively, wrote on their paper.

They reported that these waves are focused and amplified as they approach the Earth’s surface, subsequently hurdling the magnetic field similar to the jerk observed.

“In these simulations, jerks are caused by the arrival of localized Alfvén wave packets radiated from sudden buoyancy releases inside the core,” Aubert and Finlay's research paper read. “As they reach the core surface, the waves focus their energy towards the equatorial plane and along lines of strong magnetic flux, creating sharp interannual changes in core flow and producing geomagnetic jerks through the induced variations in magnetic field acceleration.”

The findings of the study to numerically reproduce jerks introduced new ways to better understand the physical properties of Earth’s deep interior.