An analysis of solar p-mode frequencies extracted from BiSON data: 1991-1996

CHAPLIN, W. J., ELSWORTH, Y., ISAAK, G. R., LINES, R., MCLEOD, C. P., MILLER, B. A. and NEW, R. (1998). An analysis of solar p-mode frequencies extracted from BiSON data: 1991-1996. Monthly notices of the Royal Astronomical Society, 300 (4), 1077-1090.

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Link to published version:: 10.1046/j.1365-8711.1998.t01-1-01999.x

Abstract

We present a comprehensive frequency analysis of Doppler velocity observations of the visible solar disc made by the Birmingham Solar Oscillations Network (BiSON) from 1990-1996, i.e. covering the falling phase of activity cycle 22, up to and including the cycle 22/23 boundary. We have fitted low-degree (low-l) solar p modes in a variety of power spectra of differing lengths generated from these data. The analysis of the extracted frequencies reveals the expected clear solar-cycle dependence; in addition, there is now sufficient accuracy in the data to show that the low-l modal eigenfrequencies are less affected by the solar cycle than their higher l counterparts. The observed low-degree frequency shifts up to approximate to 3900 mu Hz are consistent - at the level of precision of the data - with an inverse mode-mass scaling. At frequencies above this, the blending of modes adjacent in frequency space makes it increasingly difficult to extract reliable frequency estimates. However, our data show indications of a turnover and possibly also an eventual sign change in the solar cycle shifts at frequencies above;approximate to 4000 mu Hz, as seen in higher l data. We have parametrized the observed shifts as a function of the 10.7-cm radio flux, and produced an activity-corrected, average frequency table which incorporates eigenfrequencies from 18 4-month and 9 8-month spectra. We also present the fitted frequencies from a 32-month power spectrum, generated from data collected at or close to solar minimum. In addition, we also searched for frequency asymmetries in the l = 2 mode multiplets. These could result from strong near-surface magnetic activity, or a buried magnetic field. Our fits merely place an upper limit to any mean asymmetry - over the range 10 less than or equal to n less than or equal to 21 - of between approximate to - 80 and approximate to 170 nHz (3 sigma).

Item Type: Article
Research Institute, Centre or Group: Materials and Engineering Research Institute > Thin Films Research Centre > Nanotechnology Centre for PVD Research
Identification Number: 10.1046/j.1365-8711.1998.t01-1-01999.x
Depositing User: Ann Betterton
Date Deposited: 09 Jun 2010 17:04
Last Modified: 23 Jan 2013 11:08
URI: http://shura.shu.ac.uk/id/eprint/2037

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