Solar cycle changes in the high frequency spectrum |
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Authors: | RS Ronan K Cadora BJ LaBonte |
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Institution: | (1) Center for Space Science and Astrophysics, Stanford University, 94305 Stanford, CA, USA;(2) Institute for Astronomy, University of Hawaii, 96822 Honolulu, HI, USA |
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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. |
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