Rotational shear near the solar surface as a probe for subphotospheric magnetic fields

TL;DR

This paper investigates how near-surface rotational shear in the Sun can be used to detect subphotospheric magnetic fields, finding it weakly sensitive but potentially indicative of strong magnetic fields around one kilogauss.

Contribution

It demonstrates that near-surface rotational shear can serve as a probe for strong subphotospheric magnetic fields, linking solar and red giant convective dynamics.

Findings

Shear is weakly sensitive to magnetic fields.

Strong fields (~1 kG) can be detected via shear measurements.

Radial differential rotation in red giants may share origin with solar shear.

Abstract

Helioseismology revealed an increase in the rotation rate with depth just beneath the solar surface. The relative magnitude of the radial shear is almost constant with latitude. This rotational state can be interpreted as a consequence of two conditions characteristic of the near-surface convection: the smallness of convective turnover time in comparison with the rotation period and absence of a horizontal preferred direction of convection anisotropy. The latter condition is violated in the presence of a magnetic field. This raises the question of whether the subphotospheric fields can be probed with measurements of near-surface rotational shear. The shear is shown to be weakly sensitive to magnetic fields but can serve as a probe for sufficiently strong fields of the order of one kilogauss. It is suggested that the radial differential rotation in extended convective envelopes of red giants is of the same origin as the near-surface rotational shear of the Sun.