An Examination of the Solar Torsional Oscillation

Abstract

Bands of slower and faster flow, known as solar torsional oscillations, are spatially correlated with sunspot appearances on the solar surface. Understanding the relationship between torsional oscillations and sunspots may help to illuminate the conditions of flux tube origination and motion that give rise to the sunspot cycle. This, in turn, may help to understand the process of dipolar magnetic field generation in the sun. In order to better understand the formation and behavior of the torsional oscillation in the presence of convection, magnetohydrodynamic code, with magnetic feedback removed, was used to model the convection zone. In baseline simulations, a fairly consistent signal at the torsional oscillation frequency was detected near the top of the tachocline at mid-latitudes. When a mechanical forcing representing the torsional oscillation was added, it diffused but did not propagate, in contrast to previous works. When the signal varied with latitude, a region of active attenuation was noted at 30° N and S latitudes. These results indicate that specific convection patterns at the top of the tachocline may be responsible for flux tube origination. Further, mechanical forcing alone is insufficient to generate a torsional oscillation in this type of model.