Deep-Focus Diagnostics of Sunspot Structure
  In sequel to Moradi et al. [2009, ApJ, 690, L72], we employ two established numerical forward models (a 3D ideal MHD solver and MHD ray theory) in conjunction with time-distance helioseismology to probe the lateral extent of wave-speed perturbations produced in regions of strong, near-surface magnetic fields. We continue our comparisons of forward modeling approaches by extending our previous surface-focused travel-time measurements with a common midpoint deep-focusing scheme that avoids the use of oscillation signals within the sunspot region. The idea is to also test MHD ray theory for possible application in future inverse methods. 
H. Moradi, S. M. Hanasoge
astro-ph.SR