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Title:
Acoustic absorption by sunspots
Authors:
Braun, D. C.; Duvall, T. L., Jr.; Labonte, B. J.
Affiliation:
AA(Hawaii, University, Honolulu), AB(NASA, Goddard Space Flight Center, Greenbelt, MD), AC(Hawaii, University, Honolulu)
Publication:
Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X), vol. 319, Aug. 1, 1987, p. L27-L31. (ApJL Homepage)
Publication Date:
08/1987
Category:
Solar Physics
Origin:
STI
NASA/STI Keywords:
Photosphere, Solar Atmosphere, Solar Oscillations, Sound Waves, Sunspots, Hankel Functions, Helioseismology, Propagation Velocity, Vibration Mode, Wave Propagation
DOI:
10.1086/184949
Bibliographic Code:
1987ApJ...319L..27B

Abstract

The paper presents the initial results of a series of observations designed to probe the nature of sunspots by detecting their influence on high-degree p-mode oscillations in the surrounding photosphere. The analysis decomposes the observed oscillations into radially propagating waves described by Hankel functions in a cylindrical coordinate system centered on the sunspot. From measurements of the differences in power between waves traveling outward and inward, it is demonstrated that sunspots appear to absorb as much as 50 percent of the incoming acoustic waves. It is found that for all three sunspots observed, the amount of absorption increases linearly with horizontal wavenumber. The effect is present in p-mode oscillations with wavelengths both significantly larger and smaller than the diameter of the sunspot umbrae. Actual absorption of acoustic energy of the magnitude observed may produce measurable decreases in the power and lifetimes of high-degree p-mode oscillations during periods of high solar activity.

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Physics
arXiv e-prints