Indian astrophysicists unravel Sun's subsurface weather linked to 11-year activity cycle

The team, including from Stanford University (US), and the National Solar Observatory (NSO, US), traced giant tides of plasma beneath the Sun's surface at a region called near-surface shear layer (NSSL). The plasma currents shift with the Sun's magnetic heartbeat and could have far-reaching influence on space weather and Earth.

The NSSL extending to about 35,000 km in depth is a critical region beneath the Sun's surface. It is marked by distinct rotational behaviours that vary with depth and by changes, over space and time, that relate to active region magnetic fields and the solar cycle.

The study, published in The Astrophysical Journal Letters, 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.

The analysis 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 team explained.

"This is a stunning look into how the Sun's inner weather patterns form and evolve," said Professor S.P. Rajaguru, from IIA.

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," Rajaguru said.

The team deployed a technique called helioseismology -- that tracks sound waves as they travel through the Sun.

They 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 NSO.

"To validate the findings, we zoomed in on a massive sunspot region using 3D velocity maps. The localised flow patterns we observed matched the global trends -- confirming both surface inflows and deeper outflows," added lead author doctoral student Anisha Sen from IIA.

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.