Saturday, May 30, 2015


Sunspots are dark regions on the solar surface that contain complex arrangements of strong  localized magnetic fields and are often accompanied by intense solar activity (such as solar flares, coronal mass ejections), especially during the solar maximum. The dark central region of  a sunspot is called the umbra. It contains nearly vertically oriented magnetic flux tubes, which suppress the convective heat transfer. These magnetic flux tubes emerge to the solar surface at the activity belt (±30◦ latitude) and form bipolar sunspot pairs.

Due to the energy deficit the inner part of the sunspot is about 1,500 degrees cooler than the surrounding quiet Sun, therefore it appears darker against the hotter and brighter background. The semi-dark outer section of the sunspot – the penumbra is surprisingly complex. It contains bright and dark filamentary structures with varying magnetic field inclinations. The inclination of the magnetic field plays a significant role in the formation of radial plasma currents, known as the Evershed flow. In the presence of increasing magnetic inclination the granular cells become elongated magnetoconvective rolls.

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Image Credit: The Royal Swedish Academy of Sciences, Vasco M.J. Henriques/Luc Rouppe van der Voort

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