Department of Geosciences, Princeton University, New Jersey 08544, USA.
Phys Rev Lett. 2012 Sep 7;109(10):101101. doi: 10.1103/PhysRevLett.109.101101. Epub 2012 Sep 6.
Sun spots are prominent manifestations of solar magnetoconvection, and imaging their subsurface structure is an outstanding problem of wide physical importance. Travel times of seismic waves that propagate through these structures are typically used as inputs to inversions. Despite the presence of strongly anisotropic magnetic waveguides, these measurements have always been interpreted in terms of changes to isotropic wave speeds and flow-advection-related Doppler shifts. Here, we employ partial-differential-equation-constrained optimization to determine the appropriate parametrization of the structural properties of the magnetic interior. Seven different wave speeds fully characterize helioseismic wave propagation: the isotropic sound speed, a Doppler-shifting flow-advection velocity, and an anisotropic magnetic velocity. The structure of magnetic media is sensed by magnetoacoustic slow and fast modes and Alfvén waves, each of which propagates at a different wave speed. We show that even in the case of weak magnetic fields, significant errors may be incurred if these anisotropies are not accounted for in inversions. Translation invariance is demonstrably lost. These developments render plausible the accurate seismic imaging of magnetoconvection in the Sun.
太阳黑子是太阳磁对流的突出表现，对其亚表面结构进行成像，是一个具有广泛物理重要性的突出问题。穿过这些结构传播的地震波的传播时间通常被用作反演的输入。尽管存在强烈各向异性的磁波导，但这些测量结果始终根据各向同性波速的变化和与流动平流相关的多普勒频移进行解释。在这里，我们采用偏微分方程约束优化来确定磁内结构特性的适当参数化。七种不同的波速可以完全描述太阳地震波的传播：各向同性声速、多普勒频移流动平流速度和各向异性磁速。磁介质的结构通过磁声慢波和快波以及阿尔芬波来感知，每种波的传播速度都不同。我们表明，即使在磁场较弱的情况下，如果在反演中不考虑这些各向异性，也可能会导致显著的误差。平移不变性明显丧失。这些发展使得在太阳中对磁对流进行准确的地震成像成为可能。
