They Do Change After All: 25 Years of GONG Data Reveal Variation of p-Mode Energy Supply Rates

Abstract

It has been shown over and over again that the parameters of solar p modes vary through the solar activity cycle: frequencies, amplitudes, lifetimes, energies. However, so far, the rates at which energy is supplied to the p modes have not been detected to be sensitive to the level of magnetic activity. We set out to re-inspect their temporal behaviour over the course of the last two Schwabe cycles. For this, we use Global Oscillation Network Group (GONG) p-mode parameter tables. We analyse the energy supply rates for modes of harmonic degrees $l=0\text{-}150$ and average over the azimuthal orders and, subsequently, over modes in different parameter ranges. This averaging greatly helps in reducing the noise in the data.We find that energy supply rates are anti-correlated with the level of solar activity, for which we use the $F_{10.7}$ index as a proxy. Modes of different mode frequency and harmonic degrees show varying strengths of anti-correlation with the $F_{10.7}$ index, reaching as low as $r=-0.82$ for low frequency modes with $l=101\text{-}150$. In this first dedicated study of solar p-mode energy supply rates in GONG data, we find that they do indeed vary through the solar cycle. Earlier investigations with data from other instruments were hindered by being limited to low harmonic degrees or by the data sets being too short. We provide tables of time-averaged energy supply rates for individual modes as well as for averages over disjunct frequency bins.

Accepted for publication in Monthly Notices of the Royal Astronomical Society. 16 pages, 11 figures

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