Rotation suppresses giant-scale solar convection.
Rotation suppresses giant-scale solar convection.
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DOI：
10.1073/pnas.2022518118
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发表时间：
2021-08-03
影响因子：
11.1
通讯作者：
Featherstone NA
中科院分区：
文献类型：
--
作者：
Vasil GM;Julien K;Featherstone NA
整个太阳大约在28天内完成一次完整的旋转。在太阳内部30%的外部，湍流热对流推动流体向外流动。旋转使流体偏转，并确定涡流和大尺度剪切的形态。这种流动是天体物理和行星磁场产生的最终因素，这是所有科学中最重要的开放问题之一。我们的研究结果作出理论预测太阳的内部流动结构和旋转约束。我们预测，在强旋转的摇摆下，在对流区的大部分地区，都将持续存在高大细长的涡旋。我们还澄清了以前的观测差异，并解释了为什么这样的结构一直难以重现的数值模拟。在太阳外表面附近观测到的巨大对流单体的缺失是太阳建模者长期以来的难题。我们在此提出一个解释。旋转强烈影响内部动力学，导致对流速度被抑制，热传输效率增强，并且（最重要的是）相对较小的主导长度尺度。我们特别预测的特征对流长度尺度约为30毫米，整个对流区，这意味着弱流振幅在100至200毫米的巨细胞尺度，代表总信封深度。我们的推理是，科里奥利力主要平衡压力梯度（地转）。背景涡拉伸平衡斜压力矩。两者共同平衡非线性平流。湍流通量传递了辐射扩散所不能传递的太阳光度的多余部分。我们发现，这四个关系确定的主要长度尺度和动力学振幅的估计严格的已知物理量。我们预测，对流的动力Rossby数小于单位以下的近地表剪切层，表明旋转约束。
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.
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影响因子：
64.8
作者：
DUVALL, TL;JEFFERIES, SM;POMERANTZ, MA
通讯作者：
POMERANTZ, MA
影响因子：
4.9
作者：
Anders, Evan H.;Manduca, Cathryn M.;Vasil, Geoffrey M.
通讯作者：
Vasil, Geoffrey M.
影响因子：
4.9
作者：
Brown, Benjamin P.;Vasil, Geoffrey M.;Zweibel, Ellen G.
通讯作者：
Zweibel, Ellen G.
影响因子：
4.9
作者：
Barker, Adrian J.;Dempsey, Adam M.;Lithwick, Yoram
通讯作者：
Lithwick, Yoram
影响因子：
4.9
作者：
Brummell, NH;Hurlburt, NE;Toomre, J
通讯作者：
Toomre, J