A simple model for solar isorotational contours
A simple model for solar isorotational contours
复制标题
太阳等转轮廓的简单模型
DOI：
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发表时间：
2008
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影响因子：
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通讯作者：
S. Balbus
中科院分区：
文献类型：
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作者：
S. Balbus
太阳对流区，或称SCZ，几乎是绝热的，在对流上是不稳定的。但是，SCZ也处于差动旋转状态，其动力学稳定性具有弱磁化气体的性质。这使得它比流体动力系统更容易发生快速增长的旋转斜压不稳定。这些不稳定应与对流不稳定同等对待。如果等熵面和等旋面在SCZ中重合，气体对对流和旋转扰动都是边缘(不)稳定的。对于与这些更一般的旋转对流系统相关的不稳定性来说，这是一个看似合理的解决方案。这引发了对等熵和等温面相同的热风方程的分析。这个偏微分方程的特征对应于等旋等值线，即使不精确地知道熵和旋转是如何在函数上相关的，也可以推导出它们的形式。尽管全球SCZ问题的准确解决原则上需要这些知识，但即使是最简单的模型也会产生与日震学数据大致一致的惊人结果。这包括两极的水平(即准球形)等罗线、赤道的轴向等高线和中纬度的近似径向等高线。这一理论并不直接适用于塔乔跃层，在那里，简单的热风平衡是不可能有效的。本文提出的工作要经过自洽检验，其中一个检验是，在分辨率足够好的大规模数值磁流体力学模拟中，等熵线和等压线之间应该有很好的一致性。
The solar convective zone, or SCZ, is nearly adiabatic and marginally convectively unstable. But, the SCZ is also in a state of differential rotation, and its dynamical stability properties are those of a weakly magnetized gas. This renders it far more prone to rapidly growing rotational baroclinic instabilities than a hydrodynamical system would be. These instabilities should be treated on the same footing as convective instabilities. If isentropic and isorotational surfaces coincide in the SCZ, the gas is marginally (un)stable to both convective and rotational disturbances. This is a plausible resolution for the instabilities associated with these more general rotating convective systems. This motivates an analysis of the thermal wind equation in which isentropes and isorotational surfaces are identical. The characteristics of this partial differential equation correspond to isorotation contours, and their form may be deduced even without precise knowledge of how the entropy and rotation are functionally related. Although the exact solution of the global SCZ problem in principle requires this knowledge, even the simplest models produce striking results in broad agreement with helioseismology data. This includes horizontal (i.e. quasi-spherical) isorotational contours at the poles, axial contours at the equator and approximately radial contours at mid-latitudes. The theory does not apply directly to the tachocline, where a simple thermal wind balance is not expected to be valid. The work presented here is subject to tests of self-consistency, among them the prediction that there should be a good agreement between isentropes and isorotational contours in sufficiently well-resolved large-scale numerical magnetohydrodynamics simulations.