MDI observations of supergranulation
The thousands of networks of cells called supergranules that cover the Sun's surface are most easily visible in 'dopplergrams'. A dopplergram, such as this one from the SOHO spacecraft, shows motions on the Sun's surface with areas moving toward us appearing dark, and areas moving away, bright.
This image is the result of averaging 30 velocity images and subtracting the Sun's rotation, and can also be thought of as a map of the speed of the Sun's surface. Supergranules are large cells, measuring around 30 000 kilometres across (about two Earths across) but their origin and depth are currently unknown.