Angular momentum transport by the GSF instability: non-linear simulations at the equator
Angular momentum transport by the GSF instability: non-linear simulations at the equator
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GSF 不稳定性引起的角动量传递：赤道处的非线性模拟
DOI：
10.1093/mnras/stz1386
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发表时间：
2019
影响因子：
4.8
通讯作者：
Barker A
中科院分区：
文献类型：
--
作者：
Barker A
我们用轴对称和三维模拟方法研究了差动旋转辐射区赤道附近Goldreich-Schubert-Fricke(GSF)不稳定性的非线性演化。这种不稳定性可能对恒星和行星中的角动量输运做出重要贡献。我们采用局域Boussinesq笛卡尔剪切盒模型，它代表了差动旋转恒星辐射区的一小块区域。对局部径向上的无应力、不可穿透边界也进行了互补模拟。赤道轴对称不稳定性的线性和非线性演化在形式上等同于盐指不稳定性。这在3D中不再是这样，但我们发现这种不稳定性表现为类似于盐指法的非线性行为。轴对称模拟-以及沿局部方位向具有短维度的3D模拟-沿着旋转轴快速发展强大的喷流，这抑制了不稳定性，并导致了类似捕食者-猎物的时间动力学。在3D中，这种不稳定最初会产生均匀的湍流和增强的动量传输，尽管在某些情况下，喷流形成的时间尺度要长得多。我们提出并数值验证了GSF不稳定性及其角动量输运的非线性饱和的简单理论。这一理论很容易在包含旋转的恒星演化代码中实现。我们估计，GSF不稳定性可能有助于解释红巨星所需的缺失角动量输运，并在太阳角跃层的长期演化中发挥作用。
We present an investigation into the non-linear evolution of the Goldreich–Schubert–Fricke (GSF) instability using axisymmetric and 3D simulations near the equator of a differentially rotating radiation zone. This instability may provide an important contribution to angular momentum transport in stars and planets. We adopt a local Boussinesq Cartesian shearing box model, which represents a small patch of a differentially rotating stellar radiation zone. Complementary simulations are also performed with stress-free, impenetrable boundaries in the local radial direction. The linear and non-linear evolution of the equatorial axisymmetric instability is formally equivalent to the salt fingering instability. This is no longer the case in 3D, but we find that the instability behaves non-linearly in a similar way to salt fingering. Axisymmetric simulations – and those in 3D with short dimensions along the local azimuthal direction – quickly develop strong jets along the rotation axis, which inhibit the instability and lead to predator-prey-like temporal dynamics. In 3D, the instability initially produces homogeneous turbulence and enhanced momentum transport, though in some cases jets form on a much longer time-scale. We propose and validate numerically a simple theory for non-linear saturation of the GSF instability and its resulting angular momentum transport. This theory is straightforward to implement in stellar evolution codes incorporating rotation. We estimate that the GSF instability could contribute towards explaining the missing angular momentum transport required in red giant stars, and play a role in the long-term evolution of the solar tachocline.
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