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 3D 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 bring 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.

13 Pages, 3 Figures. ApJ Letters Accepted

References in corpus (4)

• Helioseismology of Sunspots: Confronting Observations with Three-Dimensional MHD Simulations of Wave Propagation
• Surface-focused Seismic Holography of Sunspots: I. Observations
• Seismic Halos Around Active Regions: An MHD Theory
• Time-Distance Modelling In A Simulated Sunspot Atmosphere

Cited by in corpus (8)

• Magnetic and Thermal Phase Shifts in the Local Helioseismology of Sunspots
• A Fixed-point Scheme for the Numerical Construction of Magnetohydrostatic Atmospheres in Three Dimensions
• Helioseismic Holography of Simulated Sunspots: dependence of the travel time on magnetic field strength and Wilson depression
• Helioseismic holography of simulated sunspots: magnetic and thermal contributions to travel times
• Directional Time-Distance Probing of Model Sunspot Atmospheres
• Exploring the Connection between Helioseismic Travel Time Anomalies and the Emergence of Large Active Regions during Solar Cycle 24
• Deep-Focus Diagnostics of Sunspot Structure
• One-sided arc averaging geometries in time-distance local helioseismology