Observational study of chromospheric heating by acoustic waves

Abstract

Aims. Our aim is to investigate the role of acoustic and magneto-acoustic waves in heating the solar chromosphere. Observations in strong chromospheric lines are analyzed by comparing the deposited acoustic-energy flux with the total integrated radiative losses. Methods. Quiet-Sun and weak-plage regions were observed in the Ca II 854.2 nm and Hα lines with the Fast Imaging Solar Spectrograph (FISS) at the 1.6-m Goode Solar Telescope on 2019 October 3 and in the Hα and Hβ lines with the echelle spectrograph attached to the Vacuum Tower Telescope on 2018 December 11 and 2019 June 6. The deposited acoustic energy flux at frequencies up to 20 mHz was derived from Doppler velocities observed in line centers and wings. Radiative losses were computed by means of a set of scaled non-local thermodynamic equilibrium 1D hydrostatic semi-empirical models obtained by fitting synthetic to observed line profiles. Results. In the middle chromosphere (h = 1000–1400 km), the radiative losses can be fully balanced by the deposited acoustic energy flux in a quiet-Sun region. In the upper chromosphere (h > 1400 km), the deposited acoustic flux is small compared to the radiative losses in quiet as well as in plage regions. The crucial parameter determining the amount of deposited acoustic flux is the gas density at a given height. Conclusions. The acoustic energy flux is efficiently deposited in the middle chromosphere, where the density of gas is sufficiently high. About 90% of the available acoustic energy flux in the quiet-Sun region is deposited in these layers, and thus it is a major contributor to the radiative losses of the middle chromosphere. In the upper chromosphere, the deposited acoustic flux is too low, so that other heating mechanisms have to act to balance the radiative cooling.

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

“…Integrating velocity power over frequency range 2-50 mHz we find that magneto-acoustic waves carry just sufficient energy to heat the chromosphere in solar plage regions. This is in contrast to the claims by Fossum & Carlsson (2005a) and recent observations by Abbasvand et al (2020).…”

“…Therefore, the energy flux available at a height of 800 km (i.e., ∼10 4 W m −2 ) is just sufficient to balance the estimated radiative losses in the layers above this height, as estimated by Withbroe & Noyes (1977). This is in contrast to previous studies where acoustic flux was found to be insufficient to compensate for the radiative losses (Fossum & Carlsson 2005b;Beck et al 2009;Abbasvand et al 2020Abbasvand et al , 2021. Additionally, the acoustic wave flux in the height range of 250-600 km is much larger than estimated in previous studies pertaining to quiet Sun regions (Wunnenberg et al 2002;Straus et al 2008;Bello González et al 2009).…”

Chromospheric Heating by Magnetohydrodynamic Waves and Instabilities

“…This way, significant portions of the radiative losses could be compensated via acoustic wave flux which has been previously converted to magnetoacoustic wave flux in the regions with the inclined fields. Abbasvand et al(2020b) concluded that the flux contained in magneto-acoustic waves with frequencies up to 20 mHz is sufficient to balance the radiative losses of the quiet chromosphere up to 1000-1400 km height. The difference with the previous results can be attributed to the existence of magnetic shadows (areas with reduced wave power at a given frequency), which prevents part of the acoustic energy reaching chromospheric heights in the network and plage regions, similar to observations by Kontogiannis et al (2014Kontogiannis et al ( , 2016.…”

Three-dimensional MHD wave propagation near a coronal null point: a new wave mode decomposition approach

“…Magnetic reconnection and heating due to waves are not independent mechanisms however, since magnetic reconnection can be a source of waves (Verwichte et al 2004;Jess et al 2008;Luna et al 2008;Li & Zhang 2012;Provornikova et al 2018), and waves can produce instabilities needed to trigger reconnection processes (Isobe & Tripathi 2006;Lee et al 2014;McLaughlin et al 2009). Moreover, recent advances in observational instrumentation and simulation capabilities imply that wave-based heating could be a viable process for maintaining the high temperatures of the solar atmosphere (Abbasvand et al 2020;Yadav et al 2021a;Abbasvand et al 2021). These new results have drawn renewed interest in wave heating mechanisms, both observationally and theoretically.…”