Slow magneto-acoustic waves in simulations of a solar plage region carry enough energy to heat the chromosphere

Abstract

Aims. We study the properties of slow magneto-acoustic waves that are naturally excited as a result of turbulent convection and we investigate their role in the energy balance of a plage region using three dimensional radiation magnetohydrodynamic simulations. Methods. To follow slow magneto-acoustic waves traveling along the magnetic field lines, we selected 25 seed locations inside a strong magnetic element and tracked the associated magnetic field lines both in space and time. We calculate the longitudinal component (i.e., parallel to the field) of velocity at each grid point along the field line and compute the temporal power spectra at various heights above the mean solar surface. Additionally, the horizontally-averaged (over the whole domain) frequency power spectra for both longitudinal and vertical (i.e., the component perpendicular to the surface) components of velocity are calculated using time series at fixed locations. To compare our results with the observations, we degrade the simulation data with Gaussian kernels having a full width at half maxium of 100 km and 200 km and calculate the horizontally-averaged power spectra for the vertical component of velocity using time series at fixed locations. Results. The power spectra of the longitudinal component of velocity, averaged over 25 field lines in the core of a kG magnetic flux concentration reveal that the dominant period of oscillations shifts from ∼6.5 min in the photosphere to ∼4 min in the chromosphere. This behavior is consistent with earlier studies that were restricted to vertically propagating waves. At the same time, the velocity power spectra, averaged horizontally over the whole domain, show that low frequency waves (∼6.5 min period) may reach well into the chromosphere. In addition, the power spectra at high frequencies follow a power law with an exponent close to −5/3, suggestive of turbulent excitation. Moreover, waves with frequencies above 5 mHz propagating along different field lines are found to be out of phase with each other, even within a single magnetic concentration. The horizontally-averaged power spectra of the vertical component of velocity at various effective resolutions show that the observed acoustic wave energy fluxes are underestimated by a factor of three, even if determined from observations carried out at a high spatial resolution of 200 km. Since the waves propagate along the non-vertical field lines, measuring the velocity component along the line-of-sight, rather than along the field, contributes significantly to this underestimation. Moreover, this underestimation of the energy flux indirectly indicates the importance of high-frequency waves that are shown to have a smaller spatial coherence and are thus more strongly influenced by the spatial averaging effect compared to low-frequency waves. Conclusions. Inside a plage region, there is on average a significant fraction of low frequency waves leaking into the chromosphere due to inclined magnetic field lines. Our results show that longitudinal waves carry (just) enough energy to heat the chromosphere in the solar plage. However, phase differences between waves traveling along different field lines within a single magnetic concentration can lead to underestimations of the wave energy flux due to averaging effects in degraded simulation data and, similarly, in observations with lower spatial resolution. We find that current observations (with spatial resolution around 200 km) underestimate the energy flux by roughly a factor of three – or more if the observations are carried out at a lower spatial resolution. We expect that even at a very high resolution, which is expected with the next generation of telescopes such as DKIST and the EST, less than half, on average, of the energy flux carried by such waves will be detected if only the line-of-sight component of the velocity is measured.

The role and contribution of magnetic fields, characterized via their magnetic flux, to the statistical structuring of the solar atmosphere

“…Therefore statistically, the quiet chromosphere may be pulsatively heated in a more frequent but less violent way than the corona, and the predominant mechanism for the coronal heating is inferred as magnetic reconnections, but for the quiet chromosphere, magnetohydrodynamic waves www.nature.com/scientificreports/ are conjectured as a significant factor. Such a scene is supported by observation and theoretical researches 35,45 (references therein). Solar wind is found to originate in coronal magnetic funnels 46 , also supporting the scene.…”

Wave transformations near a coronal magnetic null point

“…Second, p-modes are representative of convective phenomena that have typical spatial scales of 1-1.5 Mm. It is important to note that acoustic waves with higher and lower frequencies will have, correspondingly, smaller and larger spatial scales (Yadav et al 2021). Moreover, we took a smaller amplitude of the driving velocity so that perturbations remained smaller than the background quantities even after the wave propagated through our gravitationally stratified atmosphere.…”

Observations of Locally Excited Waves in the Low Solar Atmosphere Using the Daniel K. Inouye Solar Telescope

“…The study of solar acoustic waves has a history of several decades, with theoretical analyses suggesting that these waves originate from discrete dynamical events both within and below the solar photosphere. They are responsible for the resonant global p-modes, and their high-frequency components propagate upward into the solar atmosphere, potentially contributing to momentum deposition and heating (e.g., Biermann 1946;Schwarzschild 1948;Hansteen et al 2006;Kalkofen 2007;Abbasvand et al 2020;Yadav et al 2021;Molnar et al 2023 and references therein). Various mechanisms for exciting solar acoustic waves have been proposed (e.g., Lighthill 1952Lighthill , 1954Stein 1967Stein , 1991Goldreich et al 1994;Musielak et al 1994;Rast 1995Rast , 1999Samadi & Goupil 2001;Samadi et al 2007;Kitiashvili et al 2019;Zhou et al 2019Zhou et al , 2020Philidet et al 2021Philidet et al , 2022, with sporadic observational support for different mechanisms (e.g., Rimmele et al 1995;Chaplin et al 1998;Goode et al 1998;Straus et al 1999;Skartlien & Rast 2000;Strous et al 2000;Severino et al 2001;Bello González et al 2010;Roth et al 2010;Lindsey & Donea 2013;Lindsey et al 2020).…”