Magnetic Signatures of Polar Convection

Abstract:

Our inability to helioseismically image deep solar magnetism and the convective plasma motions that sustain it presents a persistent obstacle to progress in solar dynamo theory. Convective velocity measurements are largely confined to the region of near-surface shear, and vector magnetic field measurements cannot reach below the photosphere. Moreover, our vantage point of the Sun, whether from space or from the ground, has been restricted to the ecliptic plane for some time now, leaving observations confined to the Sun's low-to-mid latitude regions as a result. It is thus unfortunate that the Sun rotates. As with any rotating, convecting spherical shell, we expect its deep convective motions to differ markedly between the polar and equatorial regions. Notably, the connection between polar convective flow structure and speed has been well-explored theoretically and through nonlinear simulations. This makes observations of the Sun's polar regions particularly promising for constraining key properties of the convective flows that sustain the dynamo. We briefly summarize these earlier, non-magnetic results and then extend these fully 3-D, nonlinear simulations to incorporate magnetism. Through these models, we examine how the presence of magnetism modifies the the polar regimes of convection accessible to a star and how the large-scale magnetic field structure and strength varies across those regimes.