Understanding solar torsional oscillations from global dynamo models

Abstract

The phenomenon of solar "torsional oscillations" (TO) represents migratory zonal flows associated with the solar cycle. These flows are observed on the solar surface and, according to helioseismology, extend through the convection zone. We study the origin of the TO using results from a global MHD simulation of the solar interior that reproduces several of the observed characteristics of the mean-flows and magnetic fields. Our results indicate that the magnetic tension (MT) in the tachocline region is a key factor for the periodic changes in the angular momentum transport that causes the TO. The torque induced by the MT at the base of the convection zone is positive at the poles and negative at the equator. A rising MT torque at higher latitudes causes the poles to speed-up, whereas a declining negative MT torque at the lower latitudes causes the equator to slow-down. These changes in the zonal flows propagate through the convection zone up to the surface. Additionally, our results suggest that it is the magnetic field at the tachocline that modulates the amplitude of the surface meridional flow rather than the opposite as assumed by flux-transport dynamo models of the solar cycle.

arXiv comment16 pages, 4 figures, accepted for publication in The Astrophysical Journal Letters

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• Revisiting the Sun's Strong Differential Rotation along Radial Lines
• Turbulent processes and mean-field dynamo
• Spectral characteristic of mid-term quasi-periodicities in sunspots data
• $12660$ spotted stars toward the OGLE Galactic bulge fields
• Probing the Influence of a Tachocline in Simulated M-Dwarf Dynamos
• Meridional Circulation Dynamics in a Cyclic Convective Dynamo
• Exploring Bistability in the Cycles of the Solar Dynamo through Global Simulations
• Effects of Emerging Bipolar Magnetic Regions in Mean-field Dynamo Model of Solar Cycles 23 and 24
• Torsional Alfvénic Oscillations Discovered in the Magnetic Free Energy During Solar Flares
• Nonkinematic solar dynamo models with double-cell meridional circulation
• Implicit large eddy simulations of global solar convection: effects of numerical resolution in non-rotating and rotating cases
• Magnetic field generation in PMS stars with and without radiative core
• Numerical convergence of 2D solar convection in implicit large-eddy simulations
• Global simulations of stellar dynamos