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Frequency dependence of the solar-cycle frequency variation

Auteur

Rabello-Soares M. Cristina

Institution

Stanford University

Theme

Solar diameter, irradiance and activity

Abstract

The correlation between solar acoustic mode frequencies and the magnetic activity cycle is well established and has been substantially studied during the last two solar cycles. However, its physical origin is still a matter of debate. Libbrecht and Woodard (1990, Nature, 345, 779) were the first to suggest that the observed frequency shift is linearly proportional to the inverse mode inertia. Recently, Rabello-Soares, Korzennik and Schou (2008, Solar Physics, 251, 197) extended the analysis to high-degree modes and observed that scaling the frequency shift with the mode inertia normalized by the inertia of a radial mode of the same frequency follows a simple power law, with a different exponent for the f and p modes.

As data from the end of solar cycle 23 is now available, this analysis is revisited. Solar acoustic mode frequencies with degree up to 900 obtained by applying spherical harmonic decomposition to MDI full-disk observations are analyzed.

The dominant structural changes during the solar cycle, inasmuch as they affect the mode frequencies, is given by surface effects. After subtracting the surface effects, the frequency-shift residuals will be inverted to search for small variations of the sound speed with the solar cycle up to 0.99R.
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