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.
References
Anderson, E. R., Duvall, T. L.,Jr., and Jefferies, S. M.: 1990,Astrophys. J. 364, 699.
Balmforth, N. J. and Gough, D. O.: 1990,Astrophys. J. 362, 256.
Duvall, T. L., Jr., Harvey, J. W., Jefferies, S. M., and Pomerantz, M. A.: 1991,Astrophys. J. 373, 308.
Duvall, T. L., Jr., Jefferies, S. M., Harvey, J. W., and Pomerantz, M. A.: 1993,Nature 362, 430.
Fernandes, D. N., Scherrer, P. H., Tarbell, T. D., and Title, A. M.: 1992Astrophys. J. 392, 736.
Jefferies, S. M., Pomerantz, M. A., Duvall, T. L., Jr., Harvey, J. W., and Jaksha, D. B.: 1988, in E. Rolfe (ed.),Seismology of the Sun and Sun-like Stars, ESA SP-286, p. 279.
Kumar, P.: 1993, in T. M. Brown (ed.),GONG 1992: Seismic Investigation of the Sun and Stars, Astronomical Society of the Pacific, San Francisco, CA, p. 15.
Kumar, P. and Lu, E.: 1991,Astrophys. J. 375, L35.
Kumar, P., Duvall, T. L., Jr., Harvey, J. W., Jefferies, S. M., Pomerantz, M. A., and Thompson, M. J.: 1990, in Y. Osaki and H. Shibahashi (eds.),Progress of Seismology of the Sun and Stars, Springer, Berlin, p. 87.
Lites, B. W. and Chipman, E. G. 1979,Astrophys. J. 231, 570.
Lou, Y.: 1993,Astrophys. J. in press.
Ronan, R. S.: 1992, Ph.D. thesis, University of Hawaii, Honolulu.
Ronan, R. S. and LaBonte, B. J.: 1993,Solar Phys. in press.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Ronan, R., Cadora, K. & LaBonte, B. Solar cycle changes in the high frequency spectrum. Sol Phys 150, 389–392 (1994). https://doi.org/10.1007/BF00712900
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00712900