Hinode and IRIS observations of the magnetohydrodynamic waves propagating from the photosphere to the chromosphere in a sunspot

TL;DR

This study uses simultaneous Hinode and IRIS observations to analyze MHD waves in a sunspot, revealing their role in chromospheric heating and providing quantitative energy flux estimates at different atmospheric layers.

Contribution

It offers the first quantitative estimates of upward energy fluxes of MHD waves from the photosphere to the transition region in a sunspot, highlighting their significance in chromospheric heating.

Findings

Standing slow-mode waves dominate at the photosphere.

Upward energy flux at the photosphere exceeds chromospheric heating requirements.

Energy flux at the transition region is insufficient for coronal heating.

Abstract

Magnetohydrodynamic (MHD) waves have been considered as energy sources for heating the solar chromosphere and the corona. Although MHD waves have been observed in the solar atmosphere, there are a lack of quantitative estimates on the energy transfer and dissipation in the atmosphere. We performed simultaneous Hinode and IRIS observations of a sunspot umbra to derive the upward energy fluxes at two different atmospheric layers (photosphere and lower transition region) and estimate the energy dissipation. The observations revealed some properties of the observed periodic oscillations in physical quantities, such as their phase relations, temporal behaviors, and power spectra, making a conclusion that standing slow-mode waves are dominant at the photosphere with their high-frequency leakage, which is observed as upward waves at the chromosphere and the lower transition region. Our estimates of upward energy fluxes are $2.0\times10^7$ erg cm$^{-2}$ s$^{-1}$ at the photospheric level and $8.3\times10^4$ erg cm$^{-2}$ s$^{-1}$ at the lower transition region level. The difference between the energy fluxes is larger than the energy required to maintain the chromosphere in the sunspot umbrae, suggesting that the observed waves can make a crucial contribution to the heating of the chromosphere in the sunspot umbrae. In contrast, the upward energy flux derived at the lower transition region level is smaller than the energy flux required for heating the corona, implying that we may need another heating mechanism. We should, however, note a possibility that the energy dissipated at the chromosphere might be overestimated because of the opacity effect.