# Magnetic fields and low-frequency acoustic wave-energy supply to the solar chromosphere

## TL;DR

This study investigates how inclined magnetic fields channel low-frequency acoustic waves in the solar chromosphere, revealing higher energy fluxes than previously estimated and providing insights into wave dissipation and heating mechanisms.

## Contribution

It provides new observational evidence linking magnetic field inclination to acoustic wave propagation and energy transfer in the solar chromosphere.

## Key findings

- Acoustic energy flux is 2.25 - 2.6 kW/m², about twice previous estimates.
- Less-inclined magnetic fields channel significant low-frequency waves.
- Waves steepen and dissipate within certain chromospheric heights.

## Abstract

The problem of solar chromospheric heating remains a challenging one with wider implications for stellar physics. Several studies in the recent past have shown that small-scale inclined magnetic field elements channel copious amount of energetic low-frequency acoustic waves, that are normally trapped below the photosphere. These magneto-acoustic waves are expected to shock at chromospheric heights contributing to chromospheric heating. In this work, exploiting simultaneous photospheric vector magnetic field, Doppler, continuum and line-core intensity (of FeI 6173 {\AA}) observations from the Helioseismic and Magnetic Imager (HMI) and lower-atmospheric UV emission maps in the 1700 {\AA} and 1600 {\AA} channels of the Atmospheric Imaging Assembly (AIA), both onboard the Solar Dynamics Observatory (SDO) of NASA, we revisit the relationships between magnetic field properties (inclination and strength) and the acoustic wave propagation (phase travel time). We find that the flux of acoustic energy, in the 2 - 5 mHz frequency range, between the upper photosphere and lower chromosphere is in the range of 2.25 - 2.6 kW m$^{-2}$, which is about twice the previous estimates. We identify that the relatively less-inclined magnetic field elements in the quiet-Sun channel a significant amount of waves of frequency lower than the theoretical minimum for acoustic cut-off frequency due to magnetic inclination. We also derive indications that these waves steepen and start to dissipate within the heights ranges probed, while those let out due to inclined magnetic fields pass through. We explore connections with existing theoretical and numerical results that could explain the origin of these waves.