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Effect of nonlinear interactions on p-mode frequencies and line widths

Kumar, Pawan and Goldreich, Peter and Kerswell, Richard (1994) Effect of nonlinear interactions on p-mode frequencies and line widths. Astrophysical Journal, 427 (1). pp. 483-496. ISSN 0004-637X.

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We calculate the effect of nonlinear interactions among solar acoustic modes upon the modal frequencies and energy loss rates (or line widths). The frequency shift for a radial p-mode of frequency 3 mHz is found to be about -0.5 µHz. The magnitude of nonlinear frequency shift increases more rapidly with frequency than the inverse mode mass (mode mass is defined as the ratio of energy in the mode to its surface velocity amplitude squared). This frequency shift is primarily due to nonresonant three-mode interactions and is dominated by high l surface gravity waves (ƒ-modes) and p-modes. The line width of a radial p-mode of frequency 3 mHz, due to resonant nonlinear interactions, is about 0.3 µHz. This result is consistent with that of Kumar & Goldreich (1989). We also find, in agreement with these authors, that the most important nonlinear interactions of trapped p-modes involve ƒ-modes and high-frequency p-modes (frequency greater than about 5 mHz) which propagate in the solar photosphere. Thus, using the arguments advanced by Kumar & Goldreich (1989), we conclude that nonlinear couplings cannot saturate the overstable solar p-modes at their small observed amplitudes. Both the nonlinear frequency shifts and line widths, at a fixed frequency, are proportional to the inverse of mode mass which for modes of degree greater than about 100 is ~ l^(0.8). Therefore, the frequency of an ƒ-mode of l = 1000, due to nonlinear interactions, is decreased by approximately 0.4%.

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Additional Information:© 1994 American Astronomical Society. Received 1993 June 14; accepted 1993 November 19. We are grateful to Jorgen Christensen-Dalsgaard for supplying the solar model, Ken Libbrecht for the mode amplitude and line width data, and an anonymous referee for helpful comments. This research was supported in part by NSF grant AST 89-13664 and NASA grant NAGW-3018 with Caltech, and NASA grant W-17677 with HAO.
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NSFAST 89-13664
Subject Keywords:Sun: oscillations
Issue or Number:1
Record Number:CaltechAUTHORS:20130417-151224265
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Official Citation:Effect of nonlinear interactions on p-mode frequencies and line widths Kumar, Pawan; Goldreich, Peter; Kerswell, Richard Astrophysical Journal, vol. 427, no.1, p.483-496, 05/1994
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37999
Deposited By: Ruth Sustaita
Deposited On:19 Apr 2013 18:16
Last Modified:03 Oct 2019 04:53

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