Solar chromospheric heating by magnetohydrodynamic waves: dependence on magnetic field inclination

Abstract

A proposed mechanism for solar chromospheric heating is that magnetohydrodynamic waves propagate upward along magnetic field lines and dissipate their energy in the chromosphere. In particular, compressible magneto-acoustic waves may contribute to the heating. Theoretically, the components below the cutoff frequency cannot propagate into the chromosphere; however, the cutoff frequency depends on the inclination of the magnetic field lines. In this study, using high temporal cadence spectral data of IRIS and Hinode SOT spectropolarimeter (SP) in plages, we investigated the dependence of the low-frequency waves on magnetic-field properties and quantitatively estimated the amount of energy dissipation in the chromosphere. The following results were obtained: (a) The amount of energy dissipated by the low-frequency component (3--6 mHz) increases with the field inclination below 40 degrees, whereas it is decreased as a function of the field inclination above 40 degrees. (b) The amount of the energy is enhanced toward $10^4 W/m^2$, which is the energy required for heating in the chromospheric plage regions, when the magnetic field is higher than 600 G and inclined more than 40 degree. (c) In the photosphere, the low-frequency component has much more power in the magnetic field inclined more and weaker than 400 G. The results suggest that the observed low-frequency components can bring the energy along the magnetic field lines and that only a specific range of the field inclination angles and field strength may allow the low-frequency component to bring the sufficient amount of the energy into the chromosphere.