Rayleigh-Taylor instability in prominences from numerical simulations including partial ionization effects

Abstract

We study the Rayleigh-Taylor instability (RTI) at a prominence-corona transition region in a non-linear regime. Our aim is to understand how the presence of neutral atoms in the prominence plasma influences the instability growth rate, as well as the evolution of velocity, magnetic field vector, and thermodynamic parameters of turbulent drops. We perform 2.5D numerical simulations of the instability initiated by a multi-mode perturbation at the corona-prominence interface using a single-fluid magnetohydrodynamic (MHD) approach including a generalized Ohm's law. The initial equilibrium configuration is purely hydrostatic and contains a homogeneous horizontal magnetic field forming an angle with the direction in which the plasma is perturbed. We analyze simulations with two different orientations of the magnetic field. For each field orientation we compare two simulations, one for the pure MHD case, and one including the ambipolar diffusion in Ohm's law (AD case). Other than that, both simulations for each field orientation are identical. The numerical results in the initial stage of the instability are compared with the analytical linear calculations. We find that the configuration is always unstable in the AD case. The growth rate of the small-scale modes in the non-linear regime is up to 50% larger in the AD case than in the purely MHD case and the average velocities of flows are a few percentage points higher. Significant drift momenta are found at the interface between the coronal and the prominence material at all stages of the instability, produced by the faster downward motion of the neutral component with respect to the ionized component. The differences in temperature of the bubbles between the ideal and non-ideal case are also significant, reaching 30%. There is an asymmetry between large rising bubbles and small-scale down flowing fingers, favoring the detection of upward velocities in observations.

Two-dimensional Radiative Magnetohydrodynamic Simulations of Partial Ionization in the Chromosphere. II. Dynamics and Energetics of the Low Solar Atmosphere

“…Pedersen dissipation also allows emerging magnetic field to diffuse more rapidly into the atmosphere (Leake & Arber 2006;Arber et al 2007;Leake & Linton 2013). Compared to single-fluid simulations, 2.5D simulations of prominences including partial ionization show an increase of small-scale velocities as a result of the nonlinearity of the Rayleigh-Taylor instability Khomenko et al 2014). Further details of such processes can be found in the review by Leake et al (2014), which details the impact of ion-neutral collisions and their properties in the solar chromosphere and Earth's ionosphere.…”

Morphology and Dynamics of Solar Prominences From 3d MHD Simulations

“…Dudík et al (2012) have proposed that the existence of prominence bubbles is connected to a pair of magnetic null points associated with the prominence feet, and that a separator-reconnection scenario, which is very different from the Rayleigh-Taylor hypothesis, may naturally explain the bubble and plume formation. The role of neutrals on the MRT instability was investigated (in the linear regime) by Díaz et al (2012), while Khomenko et al (2014) have considered the nonlinear regime and have found that the configuration is always unstable on small scales. The models presented by these authors are based on local models of prominences, and the effect of the corona is not included.…”

Rayleigh-Taylor instabilities with sheared magnetic fields in partially ionised plasmas

“…We need to mention here that the existence of the critical wavenumber is very much connected to the equilibrium chosen for our model. Díaz et al (2014) and Khomenko et al (2014) studied the MRT instability of a magnetic interface with the plasma only partially ionised at both sides. They found that for such an equilibrium there is no critical wavenumber meaning that perturbations with any wavenumber are unstable.…”