Scientists Probe the Penumbra of Sunspots (ScienceFriday)
Researchers in Sweden have shed more light on how exactly sunspots are formed using a solar telescope to look at flow patterns in the penumbra or filamentary area surrounding the dark center or umbra.
The boiling motions of plasma that make up the sun are sometimes disturbed by strong, almost vertical magnetic fields that create the dark, cool centers of sunspots. Around these, the brighter penumbra comprises numerous dark and light filaments more than 1,200 miles (2,000 kilometers) long, and approximately 90 miles (150 kilometers) wide.
Led by Göran Sharmer at Stockholm University, the team discovered that the penumbra is formed by columns of hot and cold plasma that moves rapidly up and down in the area in a convective flow pattern.
The telescope showed dark downflows of up to 1 kilometer per second and bright outflows of up to 3.5 kilometers per second. These fit computer models in which columns of hot plasma rise up from inside the sunspot, widen, cool and then sink down as they flow rapidly outward.
"This is what we have been expecting to find, but we were maybe surprised about actually succeeding in seeing these flows," Göran told SPACE.com.
The scientists' findings were published online in Science on June 2.
Sunspots are of particular interest to scientists because they can be associated with coronal mass ejections and solar flares—intense bursts of solar activity that can cause geomagnetic storms which can severely disrupt sensitive systems used on Earth, such as satellites, long-range radio communications, and power grids.
