Towards Waveform Heliotomography: Observing Interactions of Helioseismic Waves with a Sunspot

Abstract

We investigate how helioseismic waves that originate from effective point sources interact with a sunspot. These waves are reconstructed from observed stochastic wavefields on the Sun by cross-correlating photospheric Doppler-velocity signals. We select the wave sources at different locations relative to the sunspot, and investigate the p- and f-mode waves separately. The results reveal a complicated picture of waveform perturbations caused by the wave interaction with the sunspot. In particular, it is found that for waves originating from outside of the sunspot, p-mode waves travel across the sunspot with a small amplitude reduction and slightly higher speed, and wave amplitude and phase get mostly restored to the quiet-Sun values after passing the sunspot. The f-mode wave experiences some amplitude reduction passing through the sunspot, and the reduced amplitude is not recovered after that. The wave-propagation speed does not change before encountering the sunspot and inside the sunspot, but the wavefront becomes faster than the reference wave after passing through the sunspot. For waves originating from inside the sunspot umbra, both f- and p-mode waves show significant amplitude reductions and faster speed during all courses of propagation. A comparison of positive and negative time lags of cross-correlation functions shows an apparent asymmetry in the waveform changes for both the f- and p-mode waves. We suggest that the waveform variations of the helioseismic waves interacting with a sunspot found in this article can be used for developing a method of waveform heliotomography, similar to the waveform tomography of the Earth.

accepted for publication in Solar Physics

References in corpus (13)

• Three Dimensional MHD Wave Propagation and Conversion to Alfven Waves near the Solar Surface. I. Direct Numerical Solution
• Helioseismology of Sunspots: A Case Study of NOAA Region 9787
• Modeling the Subsurface Structure of Sunspots
• Helioseismology of Sunspots: Confronting Observations with Three-Dimensional MHD Simulations of Wave Propagation
• Solar Flux Emergence Simulations
• High Resolution Helioseismic Imaging of Subsurface Structures and Flows of A Solar Active Region Observed by Hinode
• Surface-focused Seismic Holography of Sunspots: I. Observations
• Effect of suppressed excitation on the amplitude distribution of 5-min oscillations in sunspots
• Sensitivity of time-distance helioseismic measurements to spatial variation of oscillation amplitudes I. Observations and a numerical model
• SLiM: a code for the simulation of wave propagation through an inhomogeneous, magnetised solar atmosphere
• Constructing semi-empirical sunspot models for helioseismology
• Physical Properties of Wave Motion in Inclined Magnetic Fields Within Sunspot Penumbrae
• Determining Absorption, Emissivity Reduction, and Local Suppression Coefficients inside Sunspots

Cited by in corpus (5)

• Local Helioseismology of Sunspots: Current Status and Perspectives (Invited Review)
• Detection of Fast-Moving Waves Propagating Outward along Sunspots' Radial Direction in the Photosphere
• Dependence of sunspot photospheric waves on the depth of the source of solar $p-$modes
• Statistical analysis of the Si I 6560.58 Å line observed by CHASE
• Investigation of surface effects of simple flux tubes using numerical simulations