TY - JOUR
KW - convection
KW - star dynamics
KW - star kinematics
KW - sun interior
KW - sun rotation
KW - turbulence
AU - Loren Matilsky
AU - Bradley Hindman
AU - Juri Toomre
AB - The dynamical origins of the Sun\textquoterights tachocline and near-surface shear layer (NSSL) are still not well understood. We have attempted to self-consistently reproduce an NSSL in numerical simulations of a solar-like convection zone by increasing the density contrast across rotating 3D spherical shells. We explore the hypothesis that high density contrast leads to near-surface shear by creating a rotationally unconstrained layer of fast flows near the outer surface. Although our high-contrast models do have near-surface shear, it is confined primarily to low latitudes (between \textpm15\textdegree). Two distinct types of flow structures maintain the shear dynamically: rotationally constrained Busse columns aligned with the rotation axis and fast, rotationally unconstrained downflow plumes that deplete angular momentum from the outer fluid layers. The plumes form at all latitudes and, in fact, are more efficient at transporting angular momentum inward at high latitudes. The presence of Busse columns at low latitudes thus appears essential to creating near-surface shear in our models. We conclude that a solar-like NSSL is unobtainable from a rotationally unconstrained outer fluid layer alone. In numerical models, the shear is eliminated through the advection of angular momentum by the meridional circulation. Therefore, a detailed understanding of how the solar meridional circulation is dynamically achieved will be necessary to elucidate the origin of the Sun\textquoterights NSSL.
BT - The Astrophysical Journal
DA - 2019-02
DO - 10.3847/1538-4357/aaf647
N2 - The dynamical origins of the Sun\textquoterights tachocline and near-surface shear layer (NSSL) are still not well understood. We have attempted to self-consistently reproduce an NSSL in numerical simulations of a solar-like convection zone by increasing the density contrast across rotating 3D spherical shells. We explore the hypothesis that high density contrast leads to near-surface shear by creating a rotationally unconstrained layer of fast flows near the outer surface. Although our high-contrast models do have near-surface shear, it is confined primarily to low latitudes (between \textpm15\textdegree). Two distinct types of flow structures maintain the shear dynamically: rotationally constrained Busse columns aligned with the rotation axis and fast, rotationally unconstrained downflow plumes that deplete angular momentum from the outer fluid layers. The plumes form at all latitudes and, in fact, are more efficient at transporting angular momentum inward at high latitudes. The presence of Busse columns at low latitudes thus appears essential to creating near-surface shear in our models. We conclude that a solar-like NSSL is unobtainable from a rotationally unconstrained outer fluid layer alone. In numerical models, the shear is eliminated through the advection of angular momentum by the meridional circulation. Therefore, a detailed understanding of how the solar meridional circulation is dynamically achieved will be necessary to elucidate the origin of the Sun\textquoterights NSSL.
PY - 2019
EP - 217
T2 - The Astrophysical Journal
TI - The Role of Downflows in Establishing Solar Near-surface Shear
UR - https://iopscience.iop.org/article/10.3847/1538-4357/aaf647/meta
VL - 871
ER -