Don't be a Jerk

"Geomagnetic jerks" are abrupt changes in the strength of Earth's magnetic field. While some variations in this field are expected to occur gradually, over hundreds to thousands of years, these sudden wobbles in intensity last only a few years at most, and may only alter the Earth's magnetism over specific parts of the world at a time. One of the first jerks documented, for example, briefly warped the field over Western Europe in 1969.

Since then, a new jerk has been detected somewhere in the world every 10 years or so, and scientists still don’t know what's causing them. While many geomagnetic phenomena, including the northern and southern lights, result from electrified solar wind bashing into Earth's magnetosphere, the jerks are thought to originate from deep inside our planet's core, where the magnetic field itself is generated by the constant churn of liquid-hot iron. The exact mechanism of action, however, remains a mystery.

In the new study, the researchers built a computer model that painstakingly recreates the physical conditions of Earth's outer core, and shows its evolution over several decades. After the equivalent of 4 million hours of calculations (sped up thanks to a French supercomputer), the core simulation was able to generate geomagnetic jerks that closely aligned with actual jerks observed over the last few decades.

These simulated jerks jiggled the magnetosphere every 6 to 12 years in the model — however, the events seemed to originate from buoyant anomalies that formed in the planet's core 25 years earlier. As those blobs of molten matter approached the outer surface of the core, they generated powerful waves that rushed along magnetic field lines near the core and created "sharp changes" in the flow of liquid that governs the planet's magnetosphere, the authors wrote. Eventually, these sudden changes translate into underfoot manifested as jerky disturbances in the magnetic field high above the planet.