Author:

Keywords:

Science & Technology, Physical Sciences, Astronomy & Astrophysics, Sun: activity, Sun: chromosphere, Sun: transition region, sunspots, magnetohydrodynamics (MHD), waves, CHROMOSPHERE, PROPAGATION, PHOTOSPHERE, 0201 Astronomical and Space Sciences, 5101 Astronomical sciences, 5107 Particle and high energy physics, 5109 Space sciences

Abstract:

Context. We present a new insight into the long-standing problem of the plasma heating at the lower solar atmosphere in terms of collisional dissipation caused by two-fluid Alfv´en waves. Aims. Using numerical simulations, we study Alfv´en waves propagation and dissipation in a magnetic flux-tube and their heating effect. Methods. We set up 2.5 dimensional (2.5D) numerical simulations with a semi-empirical model of a stratified solar atmosphere and a force-free magnetic field mimicking a magnetic flux-tube. We consider a partially-ionized atmosphere consisting of ion + electron and neutral fluids which are coupled by ion-neutral collisions. Results. We find that Alfv´en waves, which are directly generated by a monochromatic driver operating at the bottom of the photosphere, experience strong damping. Low amplitude waves do not thermalize a sufficient wave energy to heat the solar atmospheric plasma. However, Alfv´en waves with amplitudes greater than 0.1 km s−1 drive through ponderomotive force magneto-acoustic waves in higher atmospheric layers. These waves are damped by ion-neutral collisions, and the thermal energy released in this process leads to heating of the upper photosphere and the chromosphere. Conclusions. We infer that, as a result of ion-neutral collisions, the energy carried initially by Alfv´en waves is thermalized in the upper photosphere and the chromosphere, and the corresponding heating rate is large enough to compensate radiative and thermal conduction energy losses therein.