Rotation suppresses giant-scale solar convection
| Autor: | Keith Julien, Nicholas A. Featherstone, Geoffrey M. Vasil |
|---|---|
| Rok vydání: | 2021 |
| Předmět: |
Length scale
Physics Convection Multidisciplinary Advection Astronomy Mechanics 01 natural sciences solar convection Physics::Fluid Dynamics Rossby number rapid rotation Convection zone Vortex stretching Physical Sciences 0103 physical sciences Astrophysics::Solar and Stellar Astrophysics Differential rotation Astrophysics::Earth and Planetary Astrophysics differential rotation 010306 general physics 010303 astronomy & astrophysics Convection cell |
| Zdroj: | Proceedings of the National Academy of Sciences of the United States of America |
| ISSN: | 1091-6490 0027-8424 |
| Popis: | Significance The entire Sun completes a full rotation in roughly 28 d. Within the outer 30% of the solar interior, turbulent thermal convection powers fluid outward. Rotation deflects the fluid and determines the morphology of eddies and large-scale shear. Such flows are the ultimate agents of astrophysical and planetary magnetic field generation, one of the most important open problems in all of science. Our results make theoretical predictions regarding the Sun’s internal flow structure and rotational constraint. We predict tall and slender vortices persisting throughout much of the convection zone under the sway of strong rotation. We also clarify previous observational discrepancies and explain why such structures have been hard to reproduce in numerical simulations. The observational absence of giant convection cells near the Sun’s outer surface is a long-standing conundrum for solar modelers. We herein propose an explanation. Rotation strongly influences the internal dynamics, leading to suppressed convective velocities, enhanced thermal-transport efficiency, and (most significantly) relatively smaller dominant length scales. We specifically predict a characteristic convection length scale of roughly 30-Mm throughout much of the convection zone, implying weak flow amplitudes at 100- to 200-Mm giant cells scales, representative of the total envelope depth. Our reasoning is such that Coriolis forces primarily balance pressure gradients (geostrophy). Background vortex stretching balances baroclinic torques. Both together balance nonlinear advection. Turbulent fluxes convey the excess part of the solar luminosity that radiative diffusion cannot. We show that these four relations determine estimates for the dominant length scales and dynamical amplitudes strictly in terms of known physical quantities. We predict that the dynamical Rossby number for convection is less than unity below the near-surface shear layer, indicating rotational constraint. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|