PERSISTENT MAGNETIC WREATHS IN A RAPIDLY ROTATING SUN

Abstract

When our Sun was young it rotated much more rapidly than now. Observations of\nyoung, rapidly rotating stars indicate that many possess substantial magnetic\nactivity and strong axisymmetric magnetic fields. We conduct simulations of\ndynamo action in rapidly rotating suns with the 3-D MHD anelastic spherical\nharmonic (ASH) code to explore the complex coupling between rotation,\nconvection and magnetism. Here we study dynamo action realized in the bulk of\nthe convection zone for a system rotating at three times the current solar\nrotation rate. We find that substantial organized global-scale magnetic fields\nare achieved by dynamo action in this system. Striking wreaths of magnetism are\nbuilt in the midst of the convection zone, coexisting with the turbulent\nconvection. This is a surprise, for it has been widely believed that such\nmagnetic structures should be disrupted by magnetic buoyancy or turbulent\npumping. Thus, many solar dynamo theories have suggested that a tachocline of\npenetration and shear at the base of the convection zone is a crucial\ningredient for organized dynamo action, whereas these simulations do not\ninclude such tachoclines. We examine how these persistent magnetic wreaths are\nmaintained by dynamo processes and explore whether a classical mean-field\n$\\alpha$-effect explains the regeneration of poloidal field.\n