GONG p-Mode Parameters Through Two Solar Cycles

Abstract

We investigate the parameters of global solar p-mode oscillations, namely damping width Γ, amplitude A, mean squared velocity ⟨v2⟩, energy E, and energy supply rate dE/dt, 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 Γ and A depends on both frequency and harmonic degree of the modes, with the largest variations of Γ for modes with 2400 μHz≤ν≤3300 μHz and 31≤l≤60 with a minimum-to-maximum variation of 26.6±0.3% and of A for modes with 2400 μHz≤ν≤3300 μHz and 61≤l≤100 with a minimum-to-maximum variation of 27.4±0.4%. The level of correlation between the solar radio flux F10.7 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 νmax=3073.59±0.18 μHz. From the mode parameters, we calculate physical mode quantities and average them over specific mode frequency ranges. In this way, we find that the mean squared velocities ⟨v2⟩ and energies E of p modes are anticorrelated with the level of activity, varying by 14.7±0.3% and 18.4±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.