Dynamics of the Solar Magnetic Network. II. Heating the Magnetized Chromosphere

TL;DR

This paper investigates how magnetoacoustic waves generated by transverse motions and acoustic absorption in magnetic flux tubes can explain the heating of the solar chromospheric network, supported by MHD models showing shock formation and wave propagation.

Contribution

It introduces detailed MHD models demonstrating that magnetoacoustic waves from flux tube motions can efficiently heat the chromosphere through shock dissipation.

Findings

Magnetoacoustic waves cause shock heating in flux tubes.

Transverse motions at flux tube bases generate effective heating.

Ambient acoustic waves are less effective unless generated near the tube axis.

Abstract

We consider recent observations of the chromospheric network, and argue that the bright network grains observed in the Ca II H & K lines are heated by an as yet unidentified quasi-steady process. We propose that the heating is caused by dissipation of short-period magnetoacoustic waves in magnetic flux tubes (periods less than 100 s). Magnetohydrodynamic (MHD) models of such waves are presented. We consider wave generation in the network due to two separate processes: (a) by transverse motions at the base of the flux tube; and (b) by the absorption of acoustic waves generated in the ambient medium. We find that the former mechanism leads to an efficient heating of the chromosphere by slow magnetoacoustic waves propagating along magnetic field lines. This heating is produced by shock waves with a horizontal size of a few hundred kilometers. In contrast, acoustic waves excited in the ambient medium are converted into transverse fast modes that travel rapidly through the flux tube and do not form shocks, unless the acoustic sources are located within 100 km from the tube axis. We conclude that the magnetic network may be heated by magnetoacoustic waves that are generated in or near the flux tubes.