Detection of large acoustic energy flux in the solar atmosphere

TL;DR

This study measures a high acoustic energy flux in the solar atmosphere using high-resolution spectropolarimetric data, suggesting acoustic waves could significantly contribute to chromospheric heating.

Contribution

It provides the first detailed measurement of acoustic energy flux at ~250 km height, showing it exceeds previous estimates and approaches the energy needed for chromospheric heating.

Findings

Measured energy flux of 6400-7700 W/m^2 at 250 km height.

Acoustic flux is mainly in intergranular lanes and dynamic granules.

Flux levels are sufficient to contribute to chromospheric energy balance.

Abstract

We study the energy flux carried by acoustic waves excited by convective motions at sub-photospheric levels. The analysis of high-resolution spectropolarimetric data taken with IMaX/Sunrise provides a total energy flux of ~ 6400--7700 Wm$^{-2}$ at a height of ~ 250 km in the 5.2-10 mHz range, i.e. at least twice the largest energy flux found in previous works. Our estimate lies within a factor of 2 of the energy flux needed to balance radiative losses from the chromosphere according to Anderson & Athay (1989) and revives interest in acoustic waves for transporting energy to the chromosphere. The acoustic flux is mainly found in the intergranular lanes but also in small rapidly-evolving granules and at the bright borders, forming dark dots and lanes of splitting granules.