Abstract
There are three major issues in modeling solar evanescent oscillations: the variation of the intensity [I]–velocity [V] phase difference of p-modes close to the base of photosphere; the existence of a plateau of negative I–V phase differences below and between the ridges of the low-frequency p-modes; the explanation of the I–V cross-spectra of the evanescent oscillations. We present new interpretations for the first two issues, based on modeling intensity fluctuations taking steep temperature gradients, opacity, and non-adiabatic cooling into account.
We also discuss consequences of our model for the explanation of power spectra and cross-power spectra of p-modes. In particular, we present evidence that the acoustic sources that generate evanescent waves produce a coherent background that explains the plateau–interridge regime of negative I–V phase difference.
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Acknowledgements
This work is dedicated to F.-L. Deubner, a pioneer of helioseismology and our master in this field. We thank the anonymous referee for making a number of very useful comments. One of the authors (GS) acknowledges financial support from the Italian Space Agency (ASI) and from the PRIN-INAF 2010 Asteroseismology: looking inside the stars with space- and ground-based observations. SDO/HMI data courtesy of NASA/SDO and the HMI science team.
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Advances in European Solar Physics
Guest Editors: Valery M. Nakariakov, Manolis K. Georgoulis, and Stefaan Poedts
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Severino, G., Straus, T., Oliviero, M. et al. The Intensity–Velocity Phase Spectra of Evanescent Oscillations and Acoustic Sources. Sol Phys 284, 297–314 (2013). https://doi.org/10.1007/s11207-012-0172-9
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DOI: https://doi.org/10.1007/s11207-012-0172-9