GoKawiilFirst look: Tiny whirlpools of magnetized plasma on the sun's surface have been captured in sharp detail for the first time, giving scientists a direct look at a long-predicted instability that could help explain how the sun stores and releases energy. Using the National Science Foundation's Daniel K. Inouye Solar Telescope on Maui, an international team recorded the highest-resolution images of the solar photosphere to date. In those images, they found dense fields of small, vortex-like structures along the edges of magnetic regions.
The patterns match what physicists expect from Kelvin-Helmholtz instability, a shear-driven effect seen in many fluids and plasmas but not previously resolved at such fine scales on the sun's visible surface. The results are detailed in a new paper in Nature, based on the telescope's 4-meter (13 foot) mirror and advanced optics that can resolve features only tens of kilometers wide.
The team focused on a magnetically active area near a sunspot, where convection cells, or granules, constantly rise and sink and magnetic fields are concentrated. In time-lapse sequences, they identified many tightly spaced vortices at the boundaries of these magnetic patches.
The distance between vortices – the instability wavelength – fell between 50 and 65 kilometers (31 to 40 miles) in both the telescope data and the numerical models, a close match that supports the idea that the structures are genuine plasma features, not artifacts.
Kelvin-Helmholtz instability occurs when neighboring layers of fluid or plasma move at different speeds, creating shear at the interface. Small disturbances grow into wave-like or spiral motions that can look like breaking waves on water or curved bands in clouds.
Scientists have documented the effect in Earth's atmosphere and oceans, in the atmospheres of gas giants such as Jupiter and Saturn, and in the interaction of the solar wind with planetary magnetic fields. On the sun, it had been predicted and hinted at in the outer corona, but direct confirmation in the photosphere required the resolution now available from the Inouye Solar Telescope.
"It has not been observed ever at that level on the solar surface," said study co-author Friedrich Wöger, a senior scientist at the National Solar Observatory.
To check their results, the researchers compared the telescope images with high-resolution magnetohydrodynamic simulations of the photosphere using the MURaM code. These simulations, developed by teams at the NSF NCAR High Altitude Observatory and the Max Planck Institute for Solar System Research, solve the core physics of plasma flow, radiation and magnetic fields. In both the simulated and observed data, fringe-like patterns at magnetic boundaries turned into similar swirling structures with comparable spacing and motion.
The work suggests that these small vortices may play more than a local role. Kelvin-Helmholtz structures can mix magnetized and non-magnetized plasma efficiently, speeding up the diffusion of magnetic fields through the lower solar atmosphere.
The analysis indicates that the mini-vortices help spread magnetic flux outward from granule edges, a process that could feed into models of the solar dynamo and the sun's 11-year magnetic cycle.
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