Chromospheric heating by acoustic waves compared to radiative cooling

TL;DR

This study compares acoustic wave energy deposition with radiative cooling in the solar chromosphere, finding that acoustic waves significantly contribute to heating, especially in active regions, though their overall impact varies.

Contribution

It provides the first detailed spatial comparison of acoustic flux and radiative losses in a solar plage, highlighting the potential dominance of acoustic heating in certain chromospheric areas.

Findings

Acoustic flux correlates with radiative losses at 72% spatially.

In quiet chromosphere, acoustic contribution is about 15%.

In active regions, acoustic contribution ranges from 23% to 54%.

Abstract

Acoustic and magnetoacoustic waves are among the possible candidate mechanisms that heat the upper layers of solar atmosphere. A weak chromospheric plage near a large solar pore NOAA 11005 was observed on October 15, 2008 in the lines Fe I 617.3 nm and Ca II 853.2 nm with the Interferometric Bidimemsional Spectrometer (IBIS) attached to the Dunn Solar Telescope. Analyzing the Ca II observations with spatial and temporal resolutions of 0.4" and 52 s, the energy deposited by acoustic waves is compared with that released by radiative losses. The deposited acoustic flux is estimated from power spectra of Doppler oscillations measured in the Ca II line core. The radiative losses are calculated using a grid of seven 1D hydrostatic semi-empirical model atmospheres. The comparison shows that the spatial correlation of maps of radiative losses and acoustic flux is 72 %. In quiet chromosphere, the contribution of acoustic energy flux to radiative losses is small, only of about 15 %. In active areas with photospheric magnetic field strength between 300 G and 1300 G and inclination of 20-60 degrees, the contribution increases from 23 % (chromospheric network) to 54 % (a plage). However, these values have to be considered as lower limits and it might be possible that the acoustic energy flux is the main contributor to the heating of bright chromospheric network and plages.