The Role of Downflows in Establishing Solar Near-Surface Shear

Abstract

The dynamical origins of the Sun's tachocline and near-surface shear layer (NSSL) are still not well understood. We have attempted to self-consistently reproduce a 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 $\pm 15^{\circ }$). Two distinct types of flow structures maintain the shear dynamically: rotationally $\text{constrained}$ Busse columns aligned with the rotation axis and fast, rotationally $\text{unconstrained}$ 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 how the solar meridional circulation is dynamically achieved will be necessary to elucidate the origin of the Sun's NSSL.

arXiv comment13 pages, 16 figures

References in corpus (14)

• Turbulent Convection Under the Influence of Rotation: Sustaining a Strong Differential Rotation
• Meridional Circulation in Solar and Stellar Convection Zones
• Differential rotation in solar-like stars from global simulations
• Zonal flow regimes in rotating anelastic spherical shells: an application to giant planets
• High-resolution calculation of the solar global convection with the reduced speed of sound technique: II. Near surface shear layer with the rotation
• Gyroscopic Pumping in the Solar Near-Surface Shear Layer
• The Spectral Amplitude of Stellar Convection and its Scaling in the High-Rayleigh-Number Regime
• Helioseismic Imaging of Fast Convective Flows Throughout the Near-Surface Shear Layer
• The Emergence of Solar Supergranulation as a Natural Consequence of Rotationally-Constrained Interior Convection
• Supergranules as Probes of the Sun's Meridional Circulation
• A Comprehensive Method to Measure Solar Meridional Circulation and Center-to-Limb Effect Using Time-Distance Helioseismology
• Helioseismic inversion to infer depth profile of solar meridional flow using spherical Born kernels
• Driving Solar Giant Cells through the Self-Organization of Near-Surface Plumes
• Multi-Ridge Fitting for Ring-Diagram Helioseismology

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