GONG p-mode parameters through two solar cycles

Abstract

We investigate the parameters of global solar p-mode oscillations, namely damping width $\Gamma$, amplitude $A$, mean squared velocity $⟨v^2⟩$, energy $E$, and energy supply rate $\mathrm{d}E/\mathrm{d}t$, derived from two solar cycles' worth (1996 - 2018) of Global Oscillation Network Group (GONG) time series for harmonic degrees $l=0-150$. We correct for the effect of fill factor, apparent solar radius, and spurious jumps in the mode amplitudes. We find that the amplitude of the activity related changes of $\Gamma$ and $A$ depends on both frequency and harmonic degree of the modes, with the largest variations of $\Gamma$ for modes with $2400\mu \text{Hz}\le \nu \le 3300\mu \text{Hz}$ and $31\le l\le 60$ with a min-to-max variation of $26.6\pm 0.3\%$ and of $A$ for modes with $2400\mu \text{Hz}\le \nu \le 3300\mu \text{Hz}$ and $61\le l\le 100$ with a min-to-max variation of $27.4\pm 0.4\%$. The level of correlation between the solar radio flux $F_{10.7}$ and mode parameters also depends on mode frequency and harmonic degree. As a function of mode frequency, the mode amplitudes are found to follow an asymmetric Voigt profile with ${\nu }_{\text{max}}=3073.59\pm 0.18\mu \text{Hz}$. From the mode parameters, we calculate physical mode quantities and average them over specific mode frequency ranges. This way, we find that the mean squared velocities $⟨v^2⟩$ and energies $E$ of p modes are anti-correlated with the level of activity, varying by $14.7\pm 0.3\%$ and $18.4\pm 0.3\%$, respectively, and that the mode energy supply rates show no significant correlation with activity. With this study we expand previously published results on the temporal variation of solar p-mode parameters. Our results will be helpful to future studies of the excitation and damping of p modes, i.e., the interplay between convection, magnetic field, and resonant acoustic oscillations.

Accepted for publication in Solar Physics. 33 pages, 16 figures, 5 tables

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