Sun-as-a-star observations: evidence for degree dependence of changes in damping of low-l p modes along the solar cycle

SALABERT, D., CHAPLIN, W. J., ELSWORTH, Y., NEW, R. and VERNER, G. A. (2007). Sun-as-a-star observations: evidence for degree dependence of changes in damping of low-l p modes along the solar cycle. Astronomy and Astrophysics Supplement Series, 463 (3), 1181-1187.

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Abstract

Aims. We use 9.5-yr of BiSON Sun-as-a-star data to search for dependence of solar-cycle parameter changes on the angular degree, l, of the data. The nature of the Sun-as-a-star observations is such that for changes measured at fixed frequency, or for changes averaged across the same range in frequency, any l dependence present carries information on the latitudinal distribution of the agent (i.e., the activity) responsible for those changes. Methods. We split the 9.5-yr timeseries into contiguous 108-d pieces, and determine mean changes in the damping of, power in, and energy supplied to the modes through the solar cycle. We also apply a careful correction to account for the deleterious effects of the ground-based BiSON window function on the results. Results. From our full analysis we obtain a marginally significant result for the damping parameter, where the mean change is found to be weakest at l = 0. The other parameters show hints of some dependence in l. Conclusions. Our main conclusion is that the mean fractional solar-cycle change in the l = 0 damping rates is approximately 50% smaller than was previously assumed. It had been common practice to use an average over all low-l modes; our downward revision of the radial-mode value has implications for comparisons with models of the global solar cycle changes, which are usually based on a spherically symmetric geometry.

Item Type:	Article
Research Institute, Centre or Group:	Materials and Engineering Research Institute > Thin Films Research Centre > Nanotechnology Centre for PVD Research
Identification Number:	10.1051/0004-6361:20066419
Depositing User:	Ann Betterton
Date Deposited:	19 May 2010 17:56
Last Modified:	19 May 2010 17:56
URI:	http://shura.shu.ac.uk/id/eprint/2082

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