Scientists uncover hidden solar link that could improve space weather forecasts

For decades, scientists have known that hot plasma slowly moves from the Sun's equator towards its poles in a process called the meridional flow.

Scientists have discovered a previously unseen connection between the Sun's surface and its upper atmosphere, offering fresh clues about the processes that drive solar activity and influence space weather that can disrupt satellites, navigation systems, communications and power grids on Earth.

The breakthrough comes from a collaborative study led by the Aryabhatta Research Institute of Observational Sciences (ARIES), an autonomous institute under the Department of Science and Technology (DST), with researchers from the Physical Research Laboratory (PRL), IIT Delhi, the Indian Institute of Space Science and Technology (IIST), and NASA's Goddard Space Flight Center. The findings have been published in The Astrophysical Journal.

Radio observations reveal hidden plasma movement

For decades, scientists have known that hot plasma slowly moves from the Sun's equator towards its poles in a process called the meridional flow. This large-scale circulation helps transport magnetic fields across the Sun and plays a central role in its 11-year solar cycle, which governs the rise and fall of sunspots and solar activity.

Until now, this movement had only been observed in the Sun's lower atmospheric layers.

The research team analysed 27 years of observations from Japan's Nobeyama Radioheliograph and found clear evidence that the same poleward flow extends nearly 3,000 kilometres above the Sun's visible surface into the upper chromosphere. This region is strongly controlled by magnetic fields, making the discovery valuable for understanding how plasma and magnetism interact throughout the solar atmosphere.

Instead of tracking individual sunspots, the scientists developed a new image-correlation technique that compared thousands of full-disk radio images taken one day apart. Measuring tiny shifts in brightness patterns over almost three decades allowed them to map large-scale plasma movement with remarkable precision.

Strong magnetic connection reaches deep inside the Sun

The study found that plasma in the upper chromosphere travels towards the poles at speeds of about 5 to 15 metres per second, closely matching the flow measured in deeper layers of the Sun. Researchers also noticed that the movement changes during different phases of the solar cycle, with the northern and southern hemispheres sometimes behaving differently depending on magnetic activity.

One of the most important discoveries came from comparing the radio observations with long-term maps of the Sun's magnetic field. Bright features detected in the radio images migrated towards the poles in close synchronisation with magnetic field transport, revealing that structures high above the Sun remain closely connected to magnetic fields rooted much deeper below the surface.

These findings provide strong observational support for the "magnetic tree" hypothesis, which suggests that magnetic structures stretching into the Sun's upper atmosphere stay connected to deeper layers much like branches remain connected to a tree's trunk and roots.

Better understanding of space weather

The discovery shows that the Sun's upper atmosphere preserves information about motions occurring deep inside the star instead of behaving as an isolated layer. This insight gives scientists a powerful new way to study the solar dynamo, the mechanism that generates the Sun's magnetic field and drives its activity cycle.

Improving knowledge of how plasma and magnetic fields move through the Sun could strengthen future space weather forecasting. Solar storms triggered by these processes can interfere with satellites, radio communication, GPS navigation and electricity networks, making accurate prediction increasingly important as the world becomes more dependent on space-based technology.

The researchers believe radio astronomy can now provide a valuable new window into the Sun's internal dynamics, helping scientists better understand the behaviour of our nearest star and its influence on Earth.