Heating of the Solar Chromosphere and Corona by Alfven Wave Turbulence

TL;DR

This paper presents a 3D MHD model demonstrating that Alfven wave turbulence, originating from small-scale photospheric motions, can account for heating in the solar chromosphere and corona, especially in active regions.

Contribution

It introduces a comprehensive 3D MHD model including lower atmospheres, showing how Alfven wave turbulence can explain heating in coronal loops and the chromosphere.

Findings

Coronal heating rate increases with magnetic field strength.

Chromospheric heating is 2-3 orders of magnitude higher than coronal heating.

Small-scale footpoint motions drive Alfven wave turbulence leading to heating.

Abstract

A three-dimensional MHD model for the propagation and dissipation of Alfven waves in a coronal loop is developed. The model includes the lower atmospheres at the two ends of the loop. The waves originate on small spatial scales (less than 100 km) inside the kilogauss flux elements in the photosphere. The model describes the nonlinear interactions between Alfven waves using the reduced MHD approximation. The increase of Alfven speed with height in the chromosphere and transition region (TR) causes strong wave reflection, which leads to counter-propagating waves and turbulence in the photospheric and chromospheric parts of the flux tube. Part of the wave energy is transmitted through the TR and produces turbulence in the corona. We find that the hot coronal loops typically found in active regions can be explained in terms of Alfven wave turbulence, provided the small-scale footpoint motions have velocities of 1-2 km/s and time scales of 60-200 s. The heating rate per unit volume in the chromosphere is 2 to 3 orders of magnitude larger than that in the corona. We construct a series of models with different values of the model parameters, and find that the coronal heating rate increases with coronal field strength and decreases with loop length. We conclude that coronal loops and the underlying chromosphere may both be heated by Alfvenic turbulence.