Geomagnetic jerks are unpredictable events that suddenly accelerate changes in the Earth's magnetic field, making its progression difficult to predict in the long term. Magnetic jerks were first described in 1978 and geophysicists have worked for decades to understand their cause.
The records of magnetic shocks date back to 1901, and a new event occurs approximately every 6-12 years. The strength of this activity is not constant across the globe, which means that only some regions may be affected. For example, in 1949, a magnetic shock was recorded in North America, which could not be detected in Europe.
In addition to protecting our planet from harmful ultraviolet radiation, the magnetic field affects numerous human activities, including the flight of low-altitude satellites. It is important for specialists to be able to understand its behavior and predict its evolution.
The Earth's magnetic field is created by the circulation of matter in its metal core, through the energy released when this core cools. There are two known types of movements that cause changes in the magnetic field. Movements resulting from slow convection can be measured on a scale of a century, and movements resulting from fast hydromagnetic waves can be detected on a scale of several years.
Experts have put forward the theory that fast hydromagnetic waves play a role in geomagnetic jerks. However, the driving force behind fast waves and their interaction with slow convection has been a mystery.
To investigate this, Julien Aubert of the University of Paris teamed up with Christopher Finlay of the Technical University of Denmark to develop computer simulations that closely resembled the physical conditions of our nucleus. The simulation required the equivalent of 4 million hours of computation, which was achieved using a supercomputer.
The researchers were able to simulate a series of events that lead to geomagnetic shocks that occur in the simulations due to hydromagnetic waves emitted in the inner core. The tremors come from rising clumps of metal that form in the planet's core 25 years before the corresponding shock.
As molten matter rises upward to reach the outer surface of the Earth's core, it produces powerful waves along magnetic field lines near the core. The team explained that this results in “dramatic changes” in the flow of fluid under a magnetic field.
According to the authors of the study, jerks represent a serious obstacle to predicting the behavior of the geomagnetic field for years to decades ahead.
However, digitally modeling and understanding these leaps will help improve these predictions.