Numerical Models of Travel-Time Inhomogeneities in Sunspots
Abstract
We investigate the direct contribution of strong, sunspot-like magnetic fields to helioseismic wave travel-time shifts via two numerical forward models, a three-dimensional ideal MHD solver and MHD ray theory. The simulated data cubes are analyzed using the traditional time-distance center-to-annulus measurement technique. We also isolate and analyze the direct contribution from purely thermal perturbations to the observed travel-time shifts, confirming some existing ideas and bringing forth new ones: (i) that the observed travel-time shifts in the vicinity of sunspots are largely governed by MHD physics, (ii) the travel-time shifts are sensitively dependent on frequency and phase-speed filter parameters and the background power below the p 1 ridge, and finally, (iii) despite its seeming limitations, ray theory succeeds in capturing the essence of the travel-time variations as derived from the MHD simulations.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2009
- DOI:
- 10.1088/0004-637X/690/1/L72
- arXiv:
- arXiv:0808.3628
- Bibcode:
- 2009ApJ...690L..72M
- Keywords:
-
- Sun: helioseismology;
- Sun: magnetic fields;
- Sun: oscillations;
- sunspots;
- Astrophysics
- E-Print:
- 13 Pages, 3 Figures. ApJ Letters Accepted