Probing the solar cycle: a comparative and complementary analysis of GONG BiSON and VIRGO/LOI eigenfrequency shifts

Details Probing the solar cycle: a comparative and complementary analysis of GONG BiSON and VIRGO/LOI eigenfrequency shifts Probing the solar cycle: a comparative and complementary analysis of GONG BiSON and VIRGO/LOI eigenfrequency shifts

Jan 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001esasp.464...83c&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,

Mathematics

Logic

2

Sun: Activity, Sun: Oscillations

Scientific paper

We use high-quality helioseismic data collected by GONG (over 4 <= l <= 140), BiSON (0 <= l <= 2) and VIRGO/LOI (0 <= l <= 8) to study the phenomenological nature of the cycle-induced (centroid) eigenfrequency variations. We have analyzed the frequency dependence of the shifts by fitting a power-law of the form δνnl ~ (νnl)α/Enl to the data (where the Enl are the mode inertias, and α is the power-law index to be extracted). Previous studies have suggested that a relation with α = 0 provides an adequate description of the shifts up to ν ≍ 3500 μHz. However, here we show that while nevertheless describing the shifts well up to ~2500 μHz, the linear scaling breaks down conspicuously at higher frequencies. Above this threshold, the shifts follow a power-law dependence with α ~ 2. We also ahow that GONG shifts, averaged over different ranges in l together with the BiSON and LOI data averaged over their full quoted ranges, all scale at fixed frequency with the normalized mode inertia ratio Qnl (Christensen-Dalsgaard & Berthomieu 1991). This is to be expected if the solar-cycle perturbation affecting the modes is confined in the surface layers; the excellent agreement also reflects favourably on the external consistency of the different observations.

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