supergranule

A supergranule is a large convection cell in the Sun's atmosphere, specifically within the photosphere. These structures are significantly larger than ordinary granules, which are the tops of smaller convection cells. Supergranules can span tens of thousands of kilometers across the Sun's surface and have a lifetime of around 24 hours. They are characterized by their relatively slow-moving plasma, with upflows at the center and downflows at the boundaries.

The existence of supergranules was first inferred from observations of the Doppler shift of spectral lines, indicating large-scale horizontal flows. These flows carry magnetic field lines towards the edges of the supergranules. This concentration of magnetic fields at the boundaries is believed to play a role in phenomena such as coronal holes and the formation of prominences. While the exact mechanisms driving supergranules are still a subject of research, they are understood to be a manifestation of convective energy transport within the Sun.