Does the excitation and damping of the acoustic eigenmodes vary over the solar cycle? An insight from LOI observations

Details Does the excitation and damping of the acoustic eigenmodes vary over the solar cycle? An insight from LOI observations Does the excitation and damping of the acoustic eigenmodes vary over the solar cycle? An insight from LOI observations

Jan 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001esasp.464..601c&link_type=abstract

In: Proceedings of the SOHO 10/GONG 2000 Workshop: Helio- and asteroseismology at the dawn of the millennium, 2-6 October 2000,

Computer Science

1

Sun: Activity, Sun: Oscillations

Scientific paper

We have used observations made by the LOI instrument on board the ESA/NASA SOHO satellite in order to try and uncover variations in the excitation and damping of the low-angular-degree solar acoustic eigenmodes over the solar cycle. These data were collected on the rising phase of activity cycle 23. We have divided the dataset into independent 136-d and 1-yr time series and fitted the modes in the complex Fourier (frequency) domain to yield estimates of the line widths and amplitudes of the modes. The extracted parameters have then been analyzed in order to search for solar-cycle-induced variations. Over the range 2600 <= ν <= 3600μHz, we uncover a mean implied activity minimum-to-maximum increase in the frequency-domain line widths of 21+/-3 per cent; a mean decrease of 37+/-3 per cent decrease in the mode heights; and a mean decrease of 18+/-4 per cent in the mode powers. Our analysis indicates that - at the level of precision of the available data - the rate at which energy is supplied to the modes remains constant (uncovered variation 3+/-5 per cent). These results are in reasonable agreement with recent claims by Chaplin et al. (2000) and Komm, Howe and Hill (2000) from analyses of BiSON and GONG data respectively. Furthermore, the signs and relative magnitudes of the extracted changes are consistent with the speculation made by Chaplin et al. that it is alterations in the damping, and not the forcing, of the modes that gives rise to the variations observed over the solar activity cycle.

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