Wave heating in gravitationally stratified coronal loops in the presence of resistivity and viscosity^⋆

¹ Centre for mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B bus 2400, 3001 Leuven, Belgium
e-mail: kostas.karampelas@kuleuven.be
² Institute of space sciences, Shandong University, Weihai 264209, PR China

Received: 24 September 2018
Accepted: 20 December 2018

Abstract

Context. In recent years, coronal loops have been the focus of studies related to the damping of different magnetohydrodynamic (MHD) surface waves and their connection with coronal seismology and wave heating. For a better understanding of wave heating, we need to take into account the effects of different dissipation coefficients such as resistivity and viscosity, the importance of the loop physical characteristics, and the ways gravity can factor into the evolution of these phenomena.

Aims. We aim to map the sites of energy dissipation from transverse waves in coronal loops in the presence and absence of gravitational stratification and to compare ideal, resistive, and viscous MHD.

Methods. Using the PLUTO code, we performed 3D MHD simulations of kink waves in single, straight, density-enhanced coronal flux tubes of multiple temperatures.

Results. We see the creation of spatially expanded Kelvin–Helmholtz eddies along the loop, which deform the initial monolithic loop profile. For the case of driven oscillations, the Kelvin–Helmholtz instability develops despite physical dissipation, unless very high values of shear viscosity are used. Energy dissipation gets its highest values near the apex, but is present all along the loop. We observe an increased efficiency of wave heating once the kinetic energy saturates at the later stages of the simulation and a turbulent density profile has developed.

Conclusions. The inclusion of gravity greatly alters the dynamic evolution of our systems and should not be ignored in future studies. Stronger physical dissipation leads to stronger wave heating in our set-ups. Finally, once the kinetic energy of the oscillating loop starts saturating, all the excess input energy turns into internal energy, resulting in more efficient wave heating.