Supergranulation

Supergranulation is a pattern of large-scale convection on the Sun’s visible surface. The cells have horizontal sizes around 20–35 megameters (Mm), with a typical diameter near 30 Mm, making them larger than granules. Individual supergranulation cells last about one to two days and are most clearly mapped by horizontal flow, via Doppler measurements or tracking of features such as granules and magnetic elements.

Flow structure: The motion is mainly horizontal, with upflows at cell centers and outward flow toward the edges, where downflows concentrate. The cell boundaries form a network that tends to trap magnetic flux, aligning with the magnetic network seen in the chromosphere.

Observations: Supergranulation appears in Doppler velocity maps, intensity images, and magnetograms. The power spectrum of horizontal flows peaks near 30 Mm. Data from space missions such as SOHO and SDO (instruments MDI and HMI) have provided detailed statistics on size, lifetime, and velocity.

Origin and interpretation: The origin is not fully settled. It is generally viewed as a near-surface convection pattern influenced by rotation and stratification, rather than a wave. The depth, driving mechanism, and relation to deeper convection remain active research topics.

Role in solar magnetism: Outward flow from cell centers drives the transport and concentration of magnetic flux at the boundaries, forming the quiet-Sun magnetic network and affecting the distribution of magnetic elements and, indirectly, the solar cycle.