The Sun’s differential rotation pattern has long been a mystery to scientists, with the poles rotating at a slower rate than the equatorial region. Advances in helioseismology, which involves studying the solar interior with the help of solar acoustic waves, have revealed that this rotational profile remains constant throughout the convection zone. This layer of the sun, which extends from approximately 200,000 kilometers below the surface to the visible solar surface, experiences violent plasma upheavals that play a crucial role in driving solar magnetism and activity.
A team of scientists from the Max Planck Institute for Solar System Research in Germany has made a groundbreaking discovery regarding the Sun’s rotational pattern. They have found that long-period solar oscillations play a key role in controlling the differential rotation of the Sun. These oscillations are similar to the baroclinically unstable waves found in Earth’s atmosphere that influence the weather. Through numerical simulations and observations from NASA’s Solar Dynamics Observatory, the researchers determined that there is a slight temperature difference between the poles and the equator, with the poles being approximately seven degrees hotter.
Despite theoretical models suggesting a temperature difference between the poles and equator to maintain the Sun’s rotational pattern, measuring this difference has been challenging due to the extreme temperatures of the Sun’s interior. However, by studying long-period oscillations observed at the solar surface, the researchers were able to determine this temperature variation. These inertial oscillations, first discovered by the MPS scientists three years ago, were found to have significant impacts on the Sun’s dynamics, particularly the high-latitude modes with velocities of up to 70 km per hour.
To further investigate the nonlinear nature of these high-latitude oscillations, the scientists conducted three-dimensional numerical simulations. These simulations revealed that the oscillations play a crucial role in carrying heat from the poles to the equator, thereby limiting the temperature difference between these regions to less than seven degrees. This small temperature disparity has a significant impact on the angular momentum balance of the Sun, influencing its global dynamics. The researchers were able to match their simulations to observational data, providing a deeper understanding of the physics behind the long-period oscillations.
The study also highlighted the similarities between the physics of solar high-latitude oscillations and extratropical cyclones on Earth. While the processes are similar, the details differ, with the solar poles being seven degrees hotter than the equator and driving flows of up to 70 kilometers per hour across a large portion of the Sun. This discovery sheds light on the active role that long-period oscillations play in the Sun’s operation and opens up avenues for future research to further explore their diagnostic potential.
This research is significant as it demonstrates the importance of the Sun’s long-period oscillations in both probing the solar interior and influencing its global dynamics. Future studies, under the ERC Synergy Grant WHOLESUN and the DFG Collaborative Research Center 1456 Mathematics of Experiments, will focus on enhancing our understanding of these oscillations and their impact on the Sun’s behavior. By continuing to investigate the role of long-period oscillations, scientists hope to gain insights into the intricate workings of our nearest star.
