Long-Period Oscillations of Sun offer new insights

Long-Period Oscillations of Sun offer new insights
by Robert Schreiber
Berlin, Germany (SPX) Mar 28, 2024

The mystery of the Sun's differential rotation, characterized by varying rotational speeds at different latitudes, has long been a subject of scientific curiosity. At the poles, a rotation cycle is completed in about 34 days, whereas at the equator, it takes approximately 24 days. Despite decades of observation and theoretical models suggesting a minor temperature variation between the solar poles and equator could account for this phenomenon, direct measurement has been elusive due to the Sun's intensely hot and opaque interior.

Recent advancements from the Max Planck Institute for Solar System Research (MPS) have provided significant insights into this puzzle. Researchers utilized data from the Helioseismic and Magnetic Imager (HMI) on NASA's Solar Dynamics Observatory spanning 2017 to 2021 to examine global solar oscillations. These oscillations, particularly potent at high latitudes with speeds reaching 70 km per hour, have been observed as swirling surface motions.

A novel approach involving three-dimensional numerical simulations allowed the team to explore the nonlinear behavior of these oscillations. The simulations revealed that these oscillations facilitate the transfer of heat from the poles to the equator, maintaining a temperature difference of less than seven degrees. According to Prof. Dr. Laurent Gizon, Director of MPS, this slight temperature variance is pivotal in regulating the Sun's angular momentum balance and is thus crucial for its overall dynamics.

This study marks the first instance of describing these processes in a fully three-dimensional context, a significant advancement over previous two-dimensional models. Dr. Yuto Bekki, MPS postdoc and lead author, emphasized that aligning these nonlinear simulations with observational data has been key to understanding the physics behind the long-period oscillations and their influence on the Sun's differential rotation.

Dr. Robert Cameron, an MPS scientist, compared the mechanism driving the solar high-latitude oscillations to the formation of extratropical cyclones on Earth, albeit under solar-specific conditions. The Sun's polar regions are about seven degrees warmer than the equator, a disparity sufficient to generate substantial flows across a significant portion of its surface.

The implications of this research extend beyond the academic, offering a deeper understanding of the Sun's internal mechanics. As part of ongoing and future investigations within the ERC Synergy Grant WHOLESUN and the DFG Collaborative Research Center 1456 Mathematics of Experiments, the study's findings promise to enhance our knowledge of these oscillations and their diagnostic capabilities, contributing to our comprehensive understanding of solar phenomena.

Research Report:The Sun's differential rotation is controlled by high-latitude baroclinically unstable inertial modes