Weak Damping of Propagating MHD Kink Waves in the Quiescent Corona

Abstract

Propagating transverse waves are thought to be a key transporter of Poynting flux throughout the Sun’s atmosphere. Recent studies have shown that these transverse motions, interpreted as the magnetohydrodynamic kink mode, are prevalent throughout the corona. The associated energy estimates suggest the waves carry enough energy to meet the demands of coronal radiative losses in the quiescent Sun. However, it is still unclear how the waves deposit their energy into the coronal plasma. We present the results from a large-scale study of propagating kink waves in the quiescent corona using data from the Coronal Multi-channel Polarimeter (CoMP). The analysis reveals that the kink waves appear to be weakly damped, which would imply low rates of energy transfer from the large-scale transverse motions to smaller scales via either uniturbulence or resonant absorption. This raises questions about how the observed kink modes would deposit their energy into the coronal plasma. Moreover, these observations, combined with the results of Monte Carlo simulations, lead us to infer that the solar corona displays a spectrum of density ratios, with a smaller density ratio (relative to the ambient corona) in quiescent coronal loops and a higher density ratio in active-region coronal loops.

A statistical study of propagating MHD kink waves in the quiescent corona

“…The catalogue is used to undertake a statistical study of the propagating kink waves providing estimates for the damping rate and propagation speeds of the waves, presenting some details of how the propagating kink waves evolve. It is found that the equilibrium parameter, which quantifies the degree of wave damping, has a broad range of values, which indicates that in some of the coronal loops, the propagating kink waves are only weakly damped (this is aspect is discussed further in Morton et al 2021). The damping length of the propagating kink waves is also estimated, which is found to be broadly comparable to the previous estimates of (Hahn & Savin 2014).…”

“…Hence, the propagating kink waves can be strongly damped or very weakly damped. The median value is ∼ 11, and a mean value of ∼ 18, which is greater than that found for the standing kink modes (see Morton et al 2021, for a full discussion of the importance of the observed values of the equilibrium parameter).…”

“…The dis-tribution of ξ presented in the left panel of Figure 4 for the positive values. The values of ξ are between 0.89 and ∼ 298; hence they occupy a wide range of values (relative to the standing modes, see Morton et al 2021). The distribution illustrates that ∼ 80 % of the positive ξ observations fall in the range of (0.89,30).…”

“…The difference in plasma parameters will ultimately bring about differences in how the waves/oscillations evolve as a function of time and/or distance. In fact, in the companion paper, Morton et al (2021), a comprehensive discussion on the implications of differences in the equilibrium parameter found for the standing waves (ξ median = 1.8) and the propagating waves (ξ median = 11.4) is provided.…”

Non-Linear Damping of Surface Alfvén Waves Due to Uniturbulence

“…Lately, Van Doorsselaere et al (2021) developed a nonlinear damping model for standing kink waves and showed that the damping time is inversely proportional to the oscillation amplitude, where they also found a notable match with the observation (Nechaeva et al, 2019). Compared to standing transverse oscillations, propagating kink waves have received little attention (Thurgood et al, 2014;Morton et al, 2021).…”