TY - JOUR
AU - Loren Matilsky
AU - Bradley Hindman
AU - Juri Toomre
AB - Current state-of-the-art models of the solar convection zone consist of solutions to the Navier-Stokes equations in rotating, 3D spherical shells. Such models are highly sensitive to the choice of boundary conditions. Here we present two suites of simulations differing only in their outer thermal boundary condition, which is either one of fixed-entropy or fixed-entropy-gradient. We find that the resulting differential rotation is markedly different between the two sets. The fixed-entropy-gradient simulations have strong differential rotation contrast and isocontours tilted along radial lines (in good agreement with the Sun's interior rotation revealed by helioseismology), while the fixed-entropy simulations have weaker contrast and contours tilted in the opposite sense. We examine in detail the force balances leading to the different rotation profiles and find that the poleward transport of heat by Busse columns plays a key role. We conclude that the Sun's strong differential rotation along radial lines may result from the solar emissivity being invariant with latitude (which is similar to the fixed-entropy-gradient condition in our models) and the poleward transport of heat by Busse columns. In future work on convection in the solar context, we strongly advise modelers to use a fixed-gradient outer boundary condition.
BT - The Astrophysical Journal
DA - 2020-07
DO - 10.3847/1538-4357/ab9ca0
IS - 2
N2 - Current state-of-the-art models of the solar convection zone consist of solutions to the Navier-Stokes equations in rotating, 3D spherical shells. Such models are highly sensitive to the choice of boundary conditions. Here we present two suites of simulations differing only in their outer thermal boundary condition, which is either one of fixed-entropy or fixed-entropy-gradient. We find that the resulting differential rotation is markedly different between the two sets. The fixed-entropy-gradient simulations have strong differential rotation contrast and isocontours tilted along radial lines (in good agreement with the Sun's interior rotation revealed by helioseismology), while the fixed-entropy simulations have weaker contrast and contours tilted in the opposite sense. We examine in detail the force balances leading to the different rotation profiles and find that the poleward transport of heat by Busse columns plays a key role. We conclude that the Sun's strong differential rotation along radial lines may result from the solar emissivity being invariant with latitude (which is similar to the fixed-entropy-gradient condition in our models) and the poleward transport of heat by Busse columns. In future work on convection in the solar context, we strongly advise modelers to use a fixed-gradient outer boundary condition.
PY - 2020
EP - 111
T2 - The Astrophysical Journal
TI - Revisiting the Sun's Strong Differential Rotation along Radial Lines
UR - https://iopscience.iop.org/article/10.3847/1538-4357/ab9ca0
VL - 898
ER -