Supergranules

Supergranules are large convective cells in the Sun's photosphere, the visible surface. They are significantly larger than the more commonly observed granules, with diameters typically ranging from 30,000 to 100,000 kilometers. These structures are characterized by slow-moving plasma flows, with material rising in the center and sinking at the edges. The lifetime of a supergranule is generally around 20 to 40 hours.

The existence of supergranules was first inferred from observations of the horizontal motions of magnetic field lines on the Sun. They are thought to be driven by convection similar to that in smaller granules, but on a much larger scale. While individual granules are fleeting, supergranules represent a more persistent, albeit slow, circulation pattern.

Supergranules play a crucial role in the transport of magnetic flux towards the Sun's edges. The outward and inward motions of plasma within a supergranular cell effectively sweep magnetic field lines towards the boundaries, a process known as the "supergranule network." This network is particularly evident in images of the Sun showing its magnetic field. The concentration of magnetic fields at the edges of supergranules is also thought to influence the appearance of phenomena like coronal holes and solar flares.