On the origin of the double cell meridional circulation in the solar convection zone

TL;DR

This paper explains the origin of the double-cell meridional circulation in the solar convection zone by showing that radial inhomogeneity of the Coriolis number, linked to convective turnover time, reproduces observed solar rotation and circulation patterns.

Contribution

It introduces a mean-field model that accounts for radial inhomogeneity of the Coriolis number, explaining the double-cell circulation pattern in the Sun's convection zone.

Findings

The model reproduces solar-like differential rotation.

It explains the double-cell meridional circulation.

Results align with observations of turbulent velocity correlations.

Abstract

Recent advances in helioseismology, numerical simulations and mean-field theory of solar differential rotation have shown that the meridional circulation pattern may consist of two or more cells in each hemisphere of the convection zone. According to the mean-field theory the double-cell circulation pattern can result from the sign inversion of a nondiffusive part of the radial angular momentum transport (the so-called $\Lambda$-effect) in the lower part of the solar convection zone. Here, we show that this phenomenon {can result} from the radial inhomogeneity of the Coriolis number, which depends on the convective turnover time. We demonstrate that if this effect is taken into account then the solar-like differential rotation and the double-cell meridional circulation are both reproduced by the mean-field model. The model is consistent with the distribution of turbulent velocity correlations determined from observations by tracing motions of sunspots and large-scale magnetic fields, indicating that these tracers are rooted just below the shear layer.