Imaging an Emerging Active Region with Helioseismic Tomography

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Abstract
The wave-speed structure beneath an emerging active region is derived from helioseismic time-distance data using inversion techniques developed in geophysics. We use Fresnel zone-based sensitivity kernels along with a Fourier domain-based regularized least-squares inversion technique. The results show that wave-speed anomalies extend down to 20 Mm below active regions. We also see some evidence of deeper anomalies that appear around 16-20 hr after the emergence of an active region and then disappear within 8 hr. These anomalies could be the signature of a change in the subsurface structure of the active region.
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