Changes to low-l solar p-mode frequencies over the solar cycle: correlations on different time-scales

CHAPLIN, W. J., ELSWORTH, Y., ISAAK, G. R., MARCHENKOV, K. I., MILLER, B. A. and NEW, R. (2001). Changes to low-l solar p-mode frequencies over the solar cycle: correlations on different time-scales. Monthly notices of the Royal Astronomical Society, 322 (1), 22-30.

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We have studied variations in the frequencies of low-l solar p modes through the analysis of nine years of helioseismic data collected by the Birmingham Solar Oscillations Network (BiSON)dagger. This is the first time that such a long data set has been explored with the extra accuracy afforded by fitting the modes to asymmetric profiles. The epoch covered (1991-99) spans the declining activity phase of solar cycle 22, and a substantial portion of the initial activity increase during cycle 23. The complete time series has been split into contiguous segments of length 27, 54, 108 and 216 d in order to facilitate the study of changes occurring on different time-scales. Further, we have characterized the observed shifts as a function of six well-known indicators of solar activity. These indices reflect changes taking place in the photosphere, chromosphere and corona, but only over the visible hemisphere of the Sun. Since the low-l eigenfrequencies respond to global variations in activity, we discuss the implications of this mismatch for the analyses performed. We demonstrate that, as expected, the low-l modes adjust to changes in the activity measures on time-scales as short as a few months. Our analysis indicates that all six proxies correlate equally well (at the level of precision of the data) with the measured shifts. Further, the sensitivity of the shifts to changes in five of the activity indices is the same, to within similar to 15 per cent (1 sigma) or so, on the falling and rising phases considered. There is, however, a slight suggestion that the sensitivity to changes in the disc-averaged line-of-sight magnetic field component (as determined from daily Kitt Peak magnetograms) may be higher on the rising phase of the cycle.

Item Type: Article
Research Institute, Centre or Group - Does NOT include content added after October 2018: Materials and Engineering Research Institute > Advanced Coatings and Composites Research Centre > Nanotechnology Centre for PVD Research
Identification Number:
Page Range: 22-30
Depositing User: Ann Betterton
Date Deposited: 09 Jun 2010 15:41
Last Modified: 19 Mar 2021 01:00

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