Dynamics of Rotation and Magnetism in the Sun's Convection Zone and Tachocline


In this thesis, we assess the theoretical dynamics achieved in the solar interior, with particular focus on the solar tachocline. We use the open-source Rayleigh code on parallel supercomputers to simulate 3-D, rotating spherical shells of convection. These shells cover much of the solar convection zone and in the tachocline models, a portion of the underlying radiative interior. This thesis divides solar dynamics into two distinct classes: The hydrodynamic (HD) Sun (which explores convection in the presence of differential rotation) and the magnetohydrodynamic (MHD) Sun (which explores how a self-excited solar dynamo interacts with convection and rotation). In the HD Sun, we discuss how the Near-Surface Shear Layer (NSSL) might be generated by fast downflow plumes. We also identify a physical mechanism whereby the Sun might establish an internal latitudinal temperature gradient and thus achieve isorotation contours significantly tilted with respect to the rotation axis. In the MHD Sun, we focus on the global magnetism and rotation profiles achieved in self-excited dynamo simulations. We first describe how dynamos in convectionzone-only shells display remarkable bistability: Two distinct magnetic cycles—each reminiscent of observed behavior in the solar cycle—are supported by the convection simultaneously. Finally, we present an MHD simulation achieving a solid-body-rotating radiative interior and differentially rotating convection zone. This shear layer, similar to the solar tachocline, is dynamically maintained by magnetic torques acting against viscous torques. Our work is thus the first to identify a “magnetic tachocline confinement scenario” operating in a fully 3-D, nonlinear global simulation. Furthermore, the magnetism is produced by dynamo action, even below the region of convective overshoot. Rather than the classical “abyssal deep”—i.e., a largely motion-free reservoir that accumulates magnetism pumped in from above—we argue that the Sun’s radiative interior may contain inertial oscillations that couple to the dynamo.

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Department of Physics
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University of Colorado Boulder
Boulder, CO
JILA PI Advisors
Advisors - Other
Bradley W. Hindman
Steven R. Cranmer
Maria D. Kazachenko
Keith Julien
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