Supergranules as Probes of Solar Convection Zone Dynamics

TL;DR

This study demonstrates that supergranules, surface convection cells on the Sun, can be used as probes to measure the rotation rate and flow dynamics of the Sun's outer convection zone, complementing helioseismology.

Contribution

It introduces a novel method of using supergranule sizes to infer the depth-dependent rotation profile of the solar convection zone.

Findings

Supergranules of different sizes probe different depths in the convection zone.

The surface shear layer extends to about 50 Mm depth and 70 degrees latitude.

Supergranules can complement helioseismology in studying solar interior dynamics.

Abstract

Supergranules are convection cells seen at the Sun's surface as a space filling pattern of horizontal flows. While typical supergranules have diameters of about 35 Mm, they exhibit a broad spectrum of sizes from ~10 Mm to ~100 Mm. Here we show that supergranules of different sizes can be used to probe the rotation rate in the Sun's outer convection zone. We find that the equatorial rotation rate as a function of depth as measured by global helioseismology matches the equatorial rotation as a function of wavelength for the supergranules. This suggests that supergranules are advected by flows at depths equal to their wavelengths and thus can be used to probe flows at those depths. The supergranule rotation profiles show that the surface shear layer, through which the rotation rate increases inward, extends to depths of ~50 Mm and to latitudes of at least 70 degrees. Typical supergranules are well observed at high latitudes and have a range of sizes that extend to greater depths than those typically available for measuring subsurface flows with local helioseismology. These characteristics indicate that probing the solar convection zone dynamics with supergranules can complement the results of helioseismology.