Dissipative instability in partially ionised prominence plasmas

TL;DR

This paper analyzes how partial ionisation and viscosity influence dissipative instabilities at the boundary between solar prominences and the corona, revealing conditions under which these instabilities occur.

Contribution

It provides a new analytical framework for understanding dissipative instability in partially ionised prominence plasmas, considering the effects of ionisation degree and viscosity.

Findings

Dissipative instabilities occur at flow speeds below Kelvin-Helmholtz threshold.

Viscosity destabilizes, while partial ionisation stabilizes the interface.

Instability in prominences has very small growth rates, unlikely to cause observed flows.

Abstract

We investigate the nature of dissipative instability at the boundary (seen here as tangential discontinuity) between the viscous corona and the partially ionised prominence plasma in the incompressible limit. The importance of the partial ionisation is investigated in terms of the ionisation fraction. Matching the solutions for the transversal component of the velocity and total pressure at the interface between the prominence and coronal plasmas, we derive a dispersion relation whose imaginary part describes the evolution of the instability. Results are obtained in the limit of weak dissipation. Using simple analytical methods, we show that dissipative instabilities appear for flow speeds that are lower than the Kelvin-Helmholtz instability threshold. While viscosity tends to destabilise the plasma, the effect of partial ionisation (through the Cowling resistivity) will act towards stabilising the interface. For ionisation degrees closer to a neutral gas the interface will be unstable for larger values of equilibrium flow. The same principle is assumed when studying the appearance of instability at the interface between prominences and dark plumes. The unstable mode appearing in this case has a very small growth rate and dissipative instability cannot explain the appearance of flows in plumes. The present study improves our understanding of the complexity of dynamical processes at the interface of solar prominences and solar corona, and the role partial ionisation can have on the stability of the plasma. Our results clearly show that the problem of partial ionisation introduces new aspects of plasma stability with consequences on the evolution of solar prominences.