Secondary small-scale dynamics of a Rayleigh-Taylor unstable solar prominence

TL;DR

The paper investigates small-scale dynamics in Rayleigh-Taylor unstable solar prominences using high-resolution 2.5D resistive MHD simulations in a 30 Mm × 30 Mm domain, achieving ~11.7 km resolution over ~10 minutes. It demonstrates how RT instability drives vertical plumes and KH shear, forming current sheets and reconnection-driven jets, and it employs synthetic EUV and Hα diagnostics to compare with observations. While many secondary structures occur at scales and durations compatible with observations, the activity concentrates in hot coronal plasma rather than the cool prominence, indicating missing physics and the need for 3D, more realistic magnetic configurations. The work highlights the importance of KH and reconnection in prominence turbulence and energy transport, and it calls for 3D modeling and inclusion of non-adiabatic processes to reconcile simulations with observed prominence dynamics.

Abstract

Quiescent solar prominences show distinct small-scale dynamics in observations. Their internal density contrasts with the surrounding corona make them susceptible to Rayleigh-Taylor (RT) instabilities, leading to vertically structured prominence morphologies when observed at the solar limb. As a result, prominences develop bubbles and plumes, along with secondary Kelvin-Helmholtz (KH) roll-ups along their edges. Recent observations also suggest magnetic reconnection events within the RT-driven turbulent flows. We perform high-resolution 2.5D resistive magnetohydrodynamic simulations using the open-source MPI-AMRVAC code, reaching a spatial resolution of $\sim 11.7$ km in a 2D domain of size 30 Mm$\times$30 Mm and evolving the system for approximately 10 minutes of solar time. A dense, magnetic pressure supported prominence serves as the initial state, which becomes unstable at the prominence-corona interface. The resulting interaction between RT and KH instabilities leads to the formation of current sheets and localized reconnection events. The reconnection-driven outflows form energetic jets that enhance energy transport and dissipation across the prominence. We analyze our high-resolution prominence simulation using synthetic images of the broadband SDO/AIA 094, 171, and 193 Å and narrowband H$α$ filters, to compare the developing fine-scale structures with their observational counterparts. Most secondary instabilities emerge in the hotter coronal regions surrounding the cooler prominence core. While our simulated features match observed scales, speeds, and duration, the simulated activity remains concentrated in hot, surrounding coronal plasma rather then the cool prominence material, implying that key physical ingredients may be missing. Future 3D studies in more realistic magnetic configurations are required to address these limitations.

Figures (12)

• Figure 1: Combined plots of $\log \rho$ and $\frac{L}{c_\mathrm{s}} \nabla \cdot \mathbf{v}$ at time 85.87 s, 429.37 s, and 618.29 s (left, middle, right) showing the evolution of bow shocks in the evolution of the solar prominence. The horizontal red dashed line indicates the 2 Mm threshold relevant for Figure \ref{['cooldense']}.
• Figure 2: Time evolution of the cool and dense solar prominence matter above the chromosphere boundary (above 2 Mm from the bottom boundary) taken below a threshold temperature of $5 \times 10^4$ K, and denser than $10^{-11}$ kg m$^{-3}$. The dashed line represents the phase of the initial decrease of mass of the cool and dense volume in the solar prominence due to the merging of the cool dense material into the chromosphere boundary. The dotted line represents the phase where the prominence material rises towards the top boundary with a significant loss of the prominence material. The solid line represents the evolution at time = 429.37 s (see Figure \ref{['density_compressibility']} (middle))
• Figure 3: Evolution of secondary KH instability in the prominence at time = 274.79, 291.97, and 343.49 s as shown in the red insets. The top row shows the zoomed image for the KH instability regions, represented as both vorticity $\nabla \times \mathbf{v}$ and Rortex R, identified using the velocity magnitude in the middle row for each time. The bottom insets show the zoom region for time = 291.97 s, representing the $v_y$ and $v_x$ component of the velocity field at that time. Together, they signal a trail of (rising) vortex structures being formed.
• Figure 4: The condition of the plasma undergoing rotational motion within the domain, as highlighted according to the R-criterion. Left; the 2.5D domain of temperature with positions of $R>5\times10^{-2}$ s$^{-1}$ and where $\lambda_\mathrm{ci} > 10 \lambda_\mathrm{cr}$ overlaid in white, see text for description of these terms. A few clear KH instability cells have been indicated with teal boxes. Right; the density -- temperature phase space of these extracted regions. A broad distribution is present, with a clear peak at the high temperatures and low densities of the solar corona. The inset axis plots the number of distinct KH cells in time (s), current time indicated by the dashed-black line, explanation in the text. An animation of this Figure will be available online.
• Figure 5: Detection of current sheets using the modified algorithm based on current density $J_z$ at time 680.12 s. The left plot shows the current density magnitude, the middle plot shows the correspondence of local maxima events using a threshold higher than the mean $|J_z|$ with the current density ($|J_{z}|$), and the right plot shows the identification of clusters derived from density clustering methodology using local maxima events at time 680.12 s. 123 separate clusters could be identified.