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Solar Physics

, Volume 150, Issue 1–2, pp 389–392 | Cite as

Solar cycle changes in the high frequency spectrum

  • R.S. Ronan
  • K. Cadora
  • B.J. LaBonte
Solar Physics Letters

Abstract

We present observations of high frequency, intermediate degree, Ca-K line solar intensity oscillations. We compare the peak frequencies determined from these 1991.4 observations with the peak frequencies from 1987.9 South Pole observations (Duvallet al., 1991) in that portion of the spatio-temporal diagram where the two datasets overlap (degrees between 30 and 150 and frequencies between 4 and 6.6 mHz). We find that temporal changes are detectable in the high frequency spectrum and are particularly large near 5.4 mHz. The m-averaged high frequency peaks decreased in frequency in 1991.4 compared to the peak frequencies measured in 1987.9. The magnitude of the frequency shift is of the order of 10 μHz near 5.4 mHz, increases with degree, and decreases to near zero both above and below 5.4 mHz. It is unlikely that these temporal changes in the high frequency spectrum are due to a change in the height of the subphotospheric acoustic source layer. A physical mechanism for these frequency shifts has not yet been identified.

Keywords

Frequency Shift Spherical Harmonic Degree High Frequency Wave High Frequency Peak Lorentzian Profile 
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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Copyright information

© Kluwer Academic Publishers 1994

Authors and Affiliations

  • R.S. Ronan
    • 1
  • K. Cadora
    • 1
  • B.J. LaBonte
    • 2
  1. 1.Center for Space Science and Astrophysics, Stanford UniversityStanfordUSA
  2. 2.Institute for Astronomy, University of HawaiiHonoluluUSA

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