Evidence for Wave Heating of the Quiet Sun Corona

TL;DR

This study provides observational evidence that Alfvénic waves carry sufficient energy to heat the quiet Sun corona, with dissipation occurring primarily at loop tops, influenced by global loop properties.

Contribution

First direct measurement of wave energy flux and dissipation regions in the quiet Sun, linking wave damping to loop length rather than local conditions.

Findings

Waves inject 1.2-5.2 x 10^5 erg cm^-2 s^-1 of energy.

Waves dissipate mainly at the top of coronal loops.

Damping onset correlates with loop length.

Abstract

We have measured the energy and dissipation of Alfvenic waves in the quiet Sun. A magnetic field was used to infer the location and orientation of the magnetic field lines along which the waves are expected to travel. The waves were measured using spectral lines to infer the wave amplitude. The waves cause a non-thermal broadening of the spectral lines, which can be expressed as a non-thermal velocity v_nt. By combining the spectroscopic measurements with this magnetic field model we were able to trace the variation of v_nt along the magnetic field. At the footpoints of the quiet Sun loops we find that waves inject an energy flux in the range of 1.2-5.2 x 10^5 erg cm^-2 s^-1. At the minimum of this range, this amounts to more than 80% of the energy needed to heat the quiet Sun. We also find that these waves are dissipated over a region centered on the top of the loops. The position along the loop where the damping begins is strongly correlated with the length of the loop, implying that the damping mechanism depends on the global loop properties rather than on local collisional dissipation.