Helioseismic Holography of Simulated Sunspots: dependence of the travel time on magnetic field strength and Wilson depression

Abstract

Improving methods for determining the subsurface structure of sunspots from their seismic signature requires a better understanding of the interaction of waves with magnetic field concentrations. We aim to quantify the impact of changes in the internal structure of sunspots on local helioseismic signals. We have numerically simulated the propagation of a stochastic wave field through sunspot models with different properties, accounting for changes in the Wilson depression between 250 and 550 km and in the photospheric umbral magnetic field between 1500 and 3500 G. The results show that travel-time shifts at frequencies above approximately 3.50 mHz (depending on the phase-speed filter) are insensitive to the magnetic field strength. The travel time of these waves is determined exclusively by the Wilson depression and sound-speed perturbation. The travel time of waves with lower frequencies is affected by the direct effect of the magnetic field, although photospheric field strengths below 1500 G do not leave a significant trace on the travel-time measurements. These results could potentially be used to develop simplified travel-time inversion methods.

Accepted for publication in A&A

References in corpus (9)

• Penumbral structure and outflows in simulated sunspots
• Three Dimensional MHD Wave Propagation and Conversion to Alfven Waves near the Solar Surface. I. Direct Numerical Solution
• Helioseismology of Sunspots: Confronting Observations with Three-Dimensional MHD Simulations of Wave Propagation
• Surface-focused Seismic Holography of Sunspots: I. Observations
• MHS sunspot model from deep sub-photospheric to chromospheric layers
• Numerical Models of Travel-Time Inhomogeneities in Sunspots
• Magnetic and Thermal Phase Shifts in the Local Helioseismology of Sunspots
• Directional Time-Distance Probing of Model Sunspot Atmospheres
• Helioseismic holography of simulated sunspots: magnetic and thermal contributions to travel times

Cited by in corpus (5)

• Numerical determination of the cutoff frequency in solar models
• Observed local dispersion relations for magneto-acoustic-gravity waves in the Sun's atmosphere: Mapping the acoustic cut-off frequency
• Improved detection of farside solar active regions using deep learning
• Performance of solar far-side active regions neural detection
• FarNet-II: An improved solar far-side active region detection method