Scientists used extensive supercomputer simulations to demonstrate the existence and importance of a small-scale dynamo in the Sun’s magnetic field. This discovery overturns previous assumptions and improves our understanding of solar dynamics, enabling earlier predictions of major solar events.
The Sun’s powerful and dynamic magnetic field can catapult giant jets Plasma known as Coronal Mass Ejections (CMEs) into the Solar System. Sometimes these crash into Earth, where they disrupt power grids and destroy satellites. Scientists do not fully understand how magnetic fields are created and amplified within the Sun, but a study recently published in the journal Natural Astronomy Answering one of the fundamental questions about this complex process. By elucidating the dynamics behind the solar climate, these findings could help predict major solar events several days in advance, giving us vital extra time to prepare.
The Sun’s magnetism arises from a process known as the solar dynamo. It consists of two main parts, a large-scale dynamo and a small-scale dynamo, neither of which scientists have yet been able to fully model. In fact, scientists aren’t even sure if a small-scale dynamo can survive in the conditions found on the Sun. Addressing uncertainty is important because small-scale dynamo can have large effects on solar dynamics.
In the new study, scientists from Aalto University and the Max Planck Institute for Solar System Research (MPS) tackled the small-scale dynamo question by running large computer simulations on petascale supercomputers in Finland and Germany. The joint computing power enabled the team to directly simulate whether the Sun had a small dynamo.
Using one of the largest computing simulations currently available, we have achieved the most realistic setting to model this dynamo,’ says Marit Korpi-Laag, Astroinformatics Group Leader and Associate Professor at Aalto University’s Department of Computer Science. ‘We have shown that not only does a small-scale dynamo exist, but that our model is more similar to the Sun and therefore more feasible.’
Some previous studies have suggested that small-scale dynamo would not work under the conditions found in Sun-like stars with very low magnetic Prandle number (PrM) used to compare the rapid variations in fluid and plasma physics. Magnetic field and velocity are equal. Korpi-Lagg’s research team modeled turbulence with unprecedentedly low PrM values and found that, contrary to thought, a small-scale dynamo could exist at such low values.
‘This is an important step towards understanding the generation of the magnetic field in the Sun and other stars,’ says John Warnecke, senior postdoctoral researcher at MPS. ‘This result will bring us closer to solving the puzzle of CME formation, which is important for protecting Earth against dangerous space weather.’
The research team is currently extending their study to even lower magnetic Prandahl number values using GPU-accelerated code on the new pan-European pre-exascale supercomputer LUMI. Next, they plan to study the interaction of the small-scale dynamo with the large-scale dynamo responsible for the 11-year solar cycle.
Reference: “Numerical evidence for a small-scale dynamo approaching solar magnetic Prandall numbers” by John Warnecke and Marit J. Corpi-Lague, Frederick A. Gent, Matthias Reinhard, 18 May 2023, Natural Astronomy.