Three-dimensional Inversion of Sound Speed below a Sunspot in the Born Approximation
Three-dimensional Inversion of Sound Speed below a Sunspot in the Born Approximation
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玻恩近似中太阳黑子下方声速的三维反演
DOI：
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发表时间：
2006
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通讯作者：
A. Kosovichev
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作者：
S. Couvidat;A. Birch;A. Kosovichev
我们修正了1998年6月太阳NOAA活动区8243下方三维声速结构的声波走时反演。我们受益于时间距离日震学的最新进展，为我们提供了更可靠的工具来推断地下太阳属性。我们在这里实现的改进之一是使用基于玻恩近似的走时灵敏度内核，该内核考虑了有限波长效应，因此比以前采用的射线路径内核更准确，通过噪声协方差矩阵在反演过程中包含太阳噪声统计特性，以及在传播时间拟合过程中的时间互协方差中使用噪声的实际方差。在这三项改进中，最重要的是玻恩近似在时距日震学中的应用。这使得这门学科的结果与基于简正波频率反演的全球日震学的结果具有相同的置信水平。此外，我们还比较了基于射线路径和玻恩近似核的反演结果。我们发现，这两种近似返回一个类似的两个区域的太阳黑子结构。然而，反演结构的深度可以偏移1或2 μ m，并且使用更现实的Born灵敏度核更准确地估计结果的空间分辨率。最后，使用安静的太阳的多普勒速度的人工实现，我们现在能够估计这些反演结果的统计不确定性。
We revise the inversion of acoustic travel times for the three-dimensional sound-speed structure below the solar NOAA Active Region 8243 of 1998 June. We benefit from recent progress in time-distance helioseismology that provides us with more reliable tools to infer subsurface solar properties. Among the improvements we implement here are the use of Born approximation-based travel-time sensitivity kernels that take into account finite-wavelength effects and thus are more accurate than the previously employed ray-path kernels, the inclusion of solar noise statistical properties in the inversion procedure through the noise covariance matrix, and the use of the actual variance of the noise in the temporal cross-covariances in the travel-time fitting procedure. Of these three improvements, the most significant is the application of the Born approximation to time-distance helioseismology. This puts the results of this discipline at the same level of confidence as those of global helioseismology based on inversion of normal-mode frequencies. Also, we compare inversion results based on ray-path and Born approximation kernels. We show that both approximations return a similar two-region structure for sunspots. However, the depth of inverted structures may be offset by 1 or 2 Mm, and the spatial resolution of the results is more accurately estimated with the more realistic Born sensitivity kernels. Finally, using artificial realizations of Doppler velocities of the quiet Sun, we are now able to estimate the statistical uncertainties of these inversion results.