KOLKATA: Plasma jets within the Sun can help foretell the erratic patterns of sunspots on its two hemispheres, allowing scientists to predict the occurrence of solar flares and space storms that sometimes render satellites useless, a study has found.
The Sun's activity waxes and wanes periodically and affects our space environment.
Sunspots, strongly magnetised blotches on the solar surface, sometimes release fierce storms in space that severely impact our satellite-based communication and navigational systems.
However, a complete understanding of all aspects of the sunspot activity cycle remains elusive.
One of its curious features is the long observed lopsided activity of its two hemispheres.
Sometimes, the northern hemisphere becomes more active, sometimes the south, with no apparent way to predict when this might happen.
Scientists from the Indian Institute of Science Education and Research (IISER) Kolkata and the Tata Institute of Fundamental Research (TIFR) in Mumbai have uncovered a link between plasma jets in the Sun's interior and the sunspot cycle which may foretell the unequal activity of the Sun's hemispheres.
Plasma-material at different locations inside the Sun rotates at different rates powering a dynamo mechanism that creates the magnetic sunspots.
The rate of rotation has been earlier observed to change with time with faster and slower streams of plasma jets known as torsional oscillations superposed on the average rotation.
These jets accompany the progress of the sunspot cycle with their patterns of migration similar to those of sunspots on the Sun's surface hinting at a causal link.
The study, published in the Astrophysical Journal of the American Astronomical Society, showed that asymmetries in plasma jets just below the Sun's surface precede asymmetries in sunspot activity by about a year, a discovery with no clear theoretical explanation yet.
"The strength of the Sun's torsional oscillation is very small compared to the differential rotation thus making it difficult to measure.
Our careful analysis covering 16 years of both ground- and space-based observations has allowed us to discover this link," said Lekshmi B, a graduate student from IISER Kolkata.
The team used a technique called helioseismology which observes oscillations on the Sun's surface that are produced by the propagation of acoustic waves in its interior.
Through use of helioseismic techniques, plasma velocity changes in the Sun's two hemispheres are then teased out.
"Our study probes only the near-surface bands of faster and slower rotation. However, the current consensus is that magnetic fields that form sunspots are created deeper inside the Sun," said Dibyendu Nandi, an associate professor at IISER Kolkata.
"It is extremely intriguing, therefore, that the sunspot cycle asymmetry is mirrored across the vast depth of the Sun's convection zone linking the deep and the near-surface layers of the Sun," said Nandi, who supervised the research in collaboration with H M Antia from TIFR.
"This may be an early manifestation of the creation of magnetic fields deep within the Sun and may lead to techniques for predicting its hemispheric activity levels" he adds.
The researchers used ground-based data from the Global Oscillation Network Group - a multinational consortium of observatories involving the US, India, Spain, Australia and Chile, and space-based data from the Helioseismic and Magnetic Imager instrument onboard NASA's Solar Dynamics Observatory.