Dynamic formation of multi-threaded prominences in arcade configurations

Abstract

Context. High in the Sun’s atmosphere, prominences are plasma structures two orders of magnitude colder and denser than the surrounding corona. They often erupt, forming the core of violent and Earth-threatening coronal mass ejections. It is still unclear how these giant structures form and what causes their internal fine structure and dynamics. Moreover, it is not evident how mass and energy get exchanged with the lower layers of the Sun’s atmosphere. Aims. We aim to understand the nature of prominences, governed by their formation process. We attempt to answer how exactly evaporation-condensation proceeds, and what the mass and energy exchange is like between the prominence and the regions where they are rooted, most notably the chromosphere and the transition region. Methods. We used a state-of-the-art threaded prominence model within a dipped magnetic arcade. We solved the non-ideal magnetohydrodynamic (MHD) equations using the open source MPI-AMRVAC MHD toolkit. Unlike many previous 1D models where a magnetic field was assumed ‘infinitely strong’, we studied the full 2D dynamics in a fixed-shaped arcade. This allowed for sideways field deformations and a cross-field thermodynamic coupling. To achieve a realistic setup, we considered field-aligned thermal conduction, radiative cooling, and heating, wherein the latter combines a steady background and a localised stochastic component. The stochastic component simulates energy pulses localised in time and space at the footpoints of the magnetic arcade. We varied the height and the amplitude of the localised heating and observed how it influences the prominence, its threads, and its overall dynamics. Results. We show with this work the importance of the random localised heating in the evolution of prominences and their threaded structure. Random heating strongly influences the morphology of the prominence threaded structure, the area, the mass the threads reach, their minimum temperature, and their average density. More importantly, the strength of the localised heating plays a role in maintaining the balance between condensation and draining, affecting the general prominence stability. Stronger sources form condensations faster and result in larger and more massive prominences. We show how the condensation rates scale with the amplitude of the heating inputs and we quantify how these rates match with values from observations. We detail how stochastic sources determine counter-streaming flows and the oscillations of prominence threads.