fibril

A characteristic feature observed in images made in hydrogen alpha light of active regions of the Sun. Fibrils show as dark streaks with a width of 725-2,200 kilometres and an average length of 11,000 kilometres. Individual fibrils have a lifetime of 10-20 minutes, though the overall fibril pattern of a region shows little change over several hours. In the central parts of active regions, fibrils are arranged in patterns connecting spots and plages of opposite polarities. Regular spots are surrounded by a radial pattern of fibrils called the superpenumbra. They represent material flowing down into the spot at velocities around 20 km/s.