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What are the observed high-frequency solar acoustic modes?

  • P. Kumar
  • T. L. DuvallJr.
  • J. W. Harvey
  • S. M. Jefferies
  • M. A. Pomerantz
  • M. J. Thompson
Part III Excitation Mechanism of Oscillations
Part of the Lecture Notes in Physics book series (LNP, volume 367)

Abstract

Jefferies et al. (1988) observe discrete peaks up to ≈7mHz in the power spectra of their intermediate degree solar intensity oscillation data obtained at South Pole. This is perhaps surprising since waves with frequency greater than the acoustic cut-off frequency at the temperature minimum (≈ 5.5mHz), unlike their lower frequency counterparts, are not trapped in the solar interior. We propose that the observed peaks are associated with what are principally progressive waves emanating from a broad-band acoustic source. The geometrical effect of projecting observations of these progressive waves onto spherical harmonics then gives rise to peaks in the power spectra. The frequencies and amplitudes of the peaks will depend on the spatial characteristics of the source. Partial reflections in the solar atmosphere modify the power spectra, but in this picture they are not the primary reason for the appearance of the peaks. We estimate the frequency and power which would be expected from this model and compare it with the observations. We argue that these high frequency “mock-modes” are not overstable, and that they are excited by acoustic emission from turbulent convection.

Keywords

Acoustic Emission Source Position High Frequency Mode Turbulent Convection Trap Mode 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. Balmforth, N., and Gough, D.O. 1990, Astrophys. J., submitted.Google Scholar
  2. Harvey, J. W. 1990, these proceedings.Google Scholar
  3. Jefferies, S.M., Pomerantz, M.A., Duvall, T.L., Jr., Harvey, J.W., and Jaksha, D.B. 1988, in Seismology of the Sun and Sun-like Stars, ed. E. Rolfe, ESA SP-286 (ESA Publication Division, Noordwijk), p.279.Google Scholar
  4. Kaufman, J.M. 1988, in Seismology of the Sun and Sun-like Stars, ed. E. Rolfe, ESA SP-286 (ESA Publication Division, Noordwijk), p.31.Google Scholar
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  7. Libbrecht, K.G. 1990, Caltech BBSO preprint no. 0305.Google Scholar

Copyright information

© Springer-Verlag 1990

Authors and Affiliations

  • P. Kumar
    • 1
  • T. L. DuvallJr.
    • 2
  • J. W. Harvey
    • 3
  • S. M. Jefferies
    • 4
  • M. A. Pomerantz
    • 4
  • M. J. Thompson
    • 1
  1. 1.HAO/NCARBoulderUSA
  2. 2.Laboratory for Astronomy and Solar PhysicsNASA/Goddard Space Flight CenterGreenbeltUSA
  3. 3.NSO/NOAOTucsonUSA
  4. 4.Bartol Research InstituteUniversity of DelawareNewarkUSA

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