Acoustic interferometry of the solar atmosphere: p-modes with frequencies near the 'acoustic cut-off' |
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| Authors: | S V Vorontsov S M Jefferies T L Duval Jr & J W Harvey |
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| Institution: | Astronomy Unit, Queen Mary and Westfield College, Mile End Road, London E1 4NS,;Institute of Physics of the Earth B., Gruzinskaya 10, Moscow 123810, Russia,;Bartol Research Institute, University of Delaware, Newark, DE 19716, USA,;Laboratory for Astronomy and Solar Physics, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA,;National Solar Observatory, PO Box 26732, Tucson, AZ 85726, USA |
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| Abstract: | High-frequency p-mode intensity data, obtained from the South Pole in 1987, 1988, 1990 and 1994, show a sharp variation in the phase-shift function and in the frequency spacings near 5.5 mHz. Using a simple theoretical model, we demonstrate that this behaviour is caused by an acoustic resonance in the atmosphere between the excitation source and the upper reflection level. We discuss the diagnostic properties of this resonance, which is sensitive to the acoustic reflectivity of the solar atmosphere and to the location and parity of the excitation source. When applied to the solar data, our model indicates that the average acoustic reflectivity increases with increasing solar activity. The model also shows that the acoustic source has composite parity and is located within one pressure scaleheight of the base of the photosphere. |
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| Keywords: | techniques: interferometric Sun: activity Sun: atmosphere Sun: oscillations |
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