An anonymous reader sends this quote from a NASA report:
"One day in the fall of 2011, Neil Sheeley, a solar scientist at the Naval Research Laboratory in Washington, D.C., did what he always does — look through the daily images of the sun from NASA's Solar Dynamics Observatory (SDO). But on this day he saw something he'd never noticed before: a pattern of cells with bright centers and dark boundaries occurring in the sun's atmosphere, the corona. ... The coronal cells occur in areas between coronal holes – colder and less dense areas of the corona seen as dark regions in images -- and "filament channels" which mark the boundaries between sections of upward-pointing magnetic fields and downward-pointing ones. Understanding how these cells evolve can provide clues as to the changing magnetic fields at the boundaries of coronal holes and how they affect the steady emission of solar material known as the solar wind streaming from these holes."