The Acoustic Showerglass. I. Seismic Diagnostics of Photospheric Magnetic Fields
The Acoustic Showerglass. I. Seismic Diagnostics of Photospheric Magnetic Fields
复制标题
声学淋浴玻璃。
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
D. Braun
中科院分区：
文献类型：
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作者：
C. Lindsey;D. Braun
活动区日震学中的一个主要问题是磁光球和浅亚光球的声学。磁场抑制了从太阳内部撞击到光球上的声波的特征，并改变了它们的相位。相移的作用就像一种声学反射镜，它削弱了从下面到达的地震波的相干性，降低了通过相位相干波的机械重建得到的地下异常图像。本研究的目的是在一般的光学术语的“声学反射镜”的特点，并作出粗略的实际评估其对当地地震诊断的浅subphotospheres活动区的影响。我们汇编统计数据，将磁性光球中的声场与来自遥远周围瞳孔的波的全息投影进行比较。这些“局部控制相关性”与活动区浅层次光球中的声学异常是一致的，这种异常很强，但主要是表面的;我们称之为“声学威尔逊凹陷”。局部控制相关性还表现出一种我们称之为“半影声学异常”的现象，其特征在于倾斜磁场区域的明显相移。这似乎是一致的一个相当简单的流体力学解释的相互作用的声波与光球磁力。声波与磁力相互作用的详细数值模拟可以极大地促进我们对声学反射玻璃和活动区亚光球顶部几百公里的热结构的理解。
A problem of major interest in the helioseismology of active regions is the acoustics of magnetic photospheres and shallow subphotospheres. Magnetic fields suppress the photospheric signatures of acoustic waves impinging onto them from the underlying solar interior and shift their phases. The phase shifts function as a sort of acoustic showerglass that impairs the coherence of seismic waves arriving from below, degrading images of subsurface anomalies derived by mechanical reconstruction of phase-coherent waves. The purpose of this study is to characterize the "acoustic showerglass" in general optical terms and make a rough practical assessment of its impact on local seismic diagnostics of the shallow subphotospheres of active regions. We compile statistics comparing the acoustic field in magnetic photospheres with holographic projections of waves arriving from distant surrounding pupils. These "local control correlations" are consistent with an acoustic anomaly in the shallow subphotosphere of the active region that is strong but predominantly superficial; we call this the "acoustic Wilson depression." The local control correlations also exhibit a phenomenon we call the "penumbral acoustic anomaly," characterized by a conspicuous phase shift in regions of inclined magnetic field. This appears to be consistent with a fairly straightforward hydromechanical interpretation of the interaction of acoustic waves with photospheric magnetic forces. Detailed numerical simulations of the interaction of acoustic waves with magnetic forces can greatly facilitate our understanding of the acoustic showerglass and the thermal structure of the top few hundred kilometers of active region subphotospheres.