Alfvén wave heating in partially ionised thin threads of solar prominences

Abstract

[eng] Quiescent solar filaments and prominences are clouds of cool and dense plasma in the solar corona suspended against gravity by forces which are supposed to be of magnetic origin. Prominences are highly dynamic structures that display oscillations that seem to be ubiquitous, as shown in observations. These oscillations are magnetohydrodynamic waves from a wide range of frequencies that are probably driven by motions in the underlying solar photosphere and may transport energy up to prominences suspended in the above corona. Dissipation of wave energy can lead to heating of the cool prominence plasma, thereby contributing to the local energy balance within the prominence. In this work we analyse the effect of Alfv´en wave dissipation as a heating mechanism in thin threads of solar prominences. We consider a 1D prominence thread model with a constant magnetic field, while the density and temperature vary along the thread in a fashion that mimics the observations. We consider Ohm’s and ambipolar diffusions and we use two different relations between the temperature and the ionisation degree. We investigate the standing and propagating modes cases using a semi-analytical approach. The results show that for the standing modes, the damping is almost negligible unless very high harmonics are considered, and the heating produced by the Alfv´en wave dissipation does not compensate the radiative cooling. For the propagating modes we have seen that the injected energy flux in the thread has relative minimums for the frequencies that correspond to the eigenfrequencies of the standing modes, which suggests the existence of resonances. For the energy balance, a broadband spectrum of propagating modes provides enough heating at the centre of the thread to compensate the cooling, but wave heating is inefficient in the hot coronal part.