Secrets of sunspots: Chinese study uncovers force behind umbral waves

Chinese researchers have recently uncovered the structure of waves within sunspots, specifically in the chromosphere, which is a part of the sun's outer layer. The researchers, from the Yunnan Observatories of the Chinese Academy of Sciences, have reported what might be driving these "umbral waves."

Studying umbral waves in sunspots enhances our understanding of solar magnetic field dynamics, energy transfer mechanisms and space weather forecasting, ultimately contributing to more accurate predictions of solar activity and its impacts on Earth.

Waves of energy are common in sunspots, and they also affect the sun's higher atmospheres. But up until now, scientists haven't been sure whether these waves were caused by forces outside the sunspot, like sound waves traveling through air, or if they came from the sunspot's own magnetic and fluid movements.

To find out, the researchers used a special instrument called the Interface Region Imaging Spectrograph, along with data from other telescopes, to take a closer look at the waves in two sunspots.

They discovered for the first time that two one-armed spiral wave patterns coexist in the umbra – the dark center of the sunspot. These patterns can spin in the same direction or in opposite ones.

Furthermore, by analyzing the spatial distribution of the oscillation centers of the one-armed spiral wave patterns within the umbra, the researchers found that the chromospheric umbral waves repeatedly come from areas with strong wave activity, especially in the sunspot's darkest and most magnetically intense regions.

The study concludes that chromospheric umbral waves are likely excited by p-mode oscillations within the sun, much like the resonant vibrations of a musical instrument stirred by the initial plucking of its strings.

The study was published in the journal Solar Physics on May 29.