Abstract
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 = 0–150 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 anticorrelated with the level of solar activity, for which we use the F10.7 index as a proxy. Modes of different mode frequency and harmonic degrees show varying strengths of anticorrelation with the F10.7 index, reaching as low as r = −0.82 for low frequency modes with l = 101–150. 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.
Highlights
Solar acoustic oscillations (p modes) are stochastically excited in the turbulent, outer convective layers of the Sun (e.g. Balmforth 1992; Rimmele et al 1995; Houdek & Dupret 2015)
Based on the results we present in this article, we conjecture that it is increased damping of oscillations and the ensuing attrition of mode amplitudes that impede the detection of stellar p-modes and need to be accounted for, but the oscillations are fed with less energy per unit time even for moderately active stars like the Sun
Contrary to the long-held opinion that the energy that is fed into the p-modes per unit time is constant, we have found that they are sensitive to the level of magnetic activity
Summary
Solar acoustic oscillations (p modes) are stochastically excited in the turbulent, outer convective layers of the Sun (e.g. Balmforth 1992; Rimmele et al 1995; Houdek & Dupret 2015). Balmforth 1992; Rimmele et al 1995; Houdek & Dupret 2015) They are well described by a damped and stochastically forced harmonic oscillator in the time domain In the Fourier domain a single p-mode peak is well characterized by a Lorentzian profile with a frequency ν, width , and height A (neglecting the observed mode asymmetry, e.g. Nigam et al 1998; Korzennik 2017; Philidet et al 2020) Measurements of these mode parameters in the Fourier domain can be used to learn about the energetics of the oscillator in the time domain: the peak width is inversely proportional to the mode’s lifetime and holds information about the damping. Possible temporal changes in the forcing function of the oscillator can be measured via time-resolved measurement of the quantity 2 · A
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