Question

what do granulation and supergranulation tell us about the sun

Answer 1

The Sun’s supergranulation is a large-scale coherent pattern detected in the surface layers of the quiet Sun. The impression given by observations is that it is simply superimposed on a stochastic, highly nonlinear background smaller-scale flow pattern, the granulation. Characterising the supergranulation velocity pattern requires monitoring solar surface flows over long times, over wide fields of views, or over a large set of independent observations.

Supergranulation has long been interpreted as a specific convection scale, but its origin is not precisely known. Although the presence of granules in the solar photosphere is a well-documented phenomenon, there is still much debate on the true nature or even the existence of higher-order granulation patterns. Some authors suggest the existence of three distinct scales of organization: granulation (with typical diameters of 150–2500 km), mesogranulation (5000–10000 km) and supergranulation (over 20000 km). Granules are typically considered as being signs of convective cells forming a hierarchic structure: supergranules would be thus fragmented in their uppermost layers into smaller mesogranules, which in turn would split into even smaller granules at their surface. The solar material would flow downward in dark "lanes" separating granules with the divisions between supergranules being the biggest concentrations of cold gas, analogous to rivers connecting smaller tributaries. It should however be stressed that this picture is highly speculative and might turn out to be false in the light of future discoveries.