Scientists chart Sun’s subsurface weather tied to its 11-year activity cycle

A global team of solar physicists has uncovered vast plasma tides moving beneath the Sun’s surface within a zone known as the near-surface shear layer (NSSL). These massive plasma flows are influenced by the Sun’s magnetic activity cycle—often referred to as its "magnetic heartbeat"—and may play a significant role in shaping space weather patterns that impact Earth.

The NSSL is a vital zone that stretches roughly 35,000 kilometers below the solar surface. This region is characterized by unique rotational patterns that shift with depth, along with spatial and temporal variations closely tied to the Sun’s magnetic fields and solar cycle. These findings offer new insights into the inner dynamics of the Sun and highlight the importance of the NSSL in understanding solar behavior and its broader effects on the heliosphere.

About The Study..

A study led by astronomers from the Indian Institute of Astrophysics (IIA), an autonomous institute of the Department of Science and Technology (DST) have probed the dynamic “inner weather” of the Sun - plasma currents just beneath its surface at the NSSL, that pulse in step with its 11-year sunspot cycle.

In the research published last week, in ‘The Astrophysical Journal Letters’, researchers from the IIA, Stanford University (USA), and the National Solar Observatory (NSO, USA) have traced how these hidden flows shift over time, potentially reshaping our understanding of solar dynamics in general and how the Sun’s interior connects to its outer magnetic behaviour in particular.  

Employing helioseismology—an advanced technique that tracks sound waves as they travel through the Sun—the team observed changes in the movement of solar material using more than a decade of data from NASA’s Solar Dynamics Observatory/ Helioseismic and Magnetic Imager (SDO/HMI) and the ground-based Global Oscillations Network Group (GONG) of National Solar Observatory (NSO), USA.
Peering Beneath the Surface

The analysis led by Professor S.P. Rajaguru and PhD student Anisha Sen from IIA revealed fascinating patterns -- surface plasma flows converge toward active sunspot latitudes, but reverse direction midway through the NSSL, flowing outward to form circulation cells. These flows are strongly influenced by the Sun’s rotation and the Coriolis force—the same force responsible for the spin of hurricanes on Earth.

The Coriolis effect swirls and shifts those inflows and outflows into a subtle but powerful sculptor of how the Sun spins at different depths, modifying the rotational shear (the gradient of rotation with depth). Yet intriguingly, these local currents do not power the Sun’s larger-scale zonal flows—known as torsional oscillations—suggesting that these global flows, which ripple through the Sun’s vast interior, must be powered by something deeper and more mysterious.

“This is a stunning look into how the Sun’s inner weather patterns form and evolve,” says Professor S.P. Rajaguru one of the authors of the paper. “Understanding these hidden patterns is not just academic—solar activity influences space weather that can disrupt satellites, power grids, and communications on Earth. This work brings us closer to understanding and building realistic models to predict the Sun’s behaviour.”

The study group also included Abhinav Govindan Iyer and other international collaborators. These findings give us a better understanding of how the Sun’s magnetic activity is linked to its internal flows and hint that we might still be missing something lurking in deeper layers that truly drives its global dynamics.