Towards Waveform Heliotomography: Observing Interactions of Helioseismic Waves with a Sunspot - Astrophysics > Solar and Stellar AstrophysicsReport as inadecuate




Towards Waveform Heliotomography: Observing Interactions of Helioseismic Waves with a Sunspot - Astrophysics > Solar and Stellar Astrophysics - Download this document for free, or read online. Document in PDF available to download.

Abstract: We investigate how helioseismic waves that originate from effective pointsources interact with a sunspot. These waves are reconstructed from observedstochastic wavefields on the Sun by cross-correlating photosphericDoppler-velocity signals. We select the wave sources at different locationsrelative to the sunspot, and investigate the p- and f-mode waves separately.The results reveal a complicated picture of waveform perturbations caused bythe wave interaction with the sunspot. In particular, it is found that forwaves originating from outside of the sunspot, p-mode waves travel across thesunspot with a small amplitude reduction and slightly higher speed, and waveamplitude and phase get mostly restored to the quiet-Sun values after passingthe sunspot. The f-mode wave experiences some amplitude reduction passingthrough the sunspot, and the reduced amplitude is not recovered after that. Thewave-propagation speed does not change before encountering the sunspot andinside the sunspot, but the wavefront becomes faster than the reference waveafter passing through the sunspot. For waves originating from inside thesunspot umbra, both f- and p-mode waves show significant amplitude reductionsand faster speed during all courses of propagation. A comparison of positiveand negative time lags of cross-correlation functions shows an apparentasymmetry in the waveform changes for both the f- and p-mode waves. We suggestthat the waveform variations of the helioseismic waves interacting with asunspot found in this article can be used for developing a method of waveformheliotomography, similar to the waveform tomography of the Earth.



Author: Junwei Zhao, Alexander G. Kosovichev, Stathis Ilonidis

Source: https://arxiv.org/







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