7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Coronal rain: plasma circulation in the solar corona
Xiaohong Li1,2, Rony Keppens2, Yuhao Zhou2
1 Max Planck Institute for Solar System Research, Germany
2
Centre for mathematical Plasma Astrophysics, KU Leuven, Belgium
e-mail (speaker): xiaohong.li@kuleuven.be
Coronal rain is a widely observed phenomenon wheredense and cool condensations form in the hot corona, andthen fall down along magnetic loops to the solar surface.
It presents us with a clear multithermal coronal plasma,
which displays the emission of different wavelengths
co-spatially. Coronal rain takes an essential part in themass cycle between the chromosphere and the corona.
Since moving magnetic features and turbulent
convection are almost ubiquitous in the solar lower
atmosphere, the formation of coronal rain is affected by
the multiscale and continuous localized heating in thesolar photosphere. Here we present 2.5-dimensional
magnetohydrodynamic simulations using theMPI-AMRVAC code, which includes thermal conduction
and radiative cooling, to investigate the formation andevolution of the coronal rain phenomenon [1]. We
perform the simulation in initially linear force-freemagnetic fields that host chromospheric,transition-region, and coronal plasma, with turbulent
heating localized on their footpoints. Due to thermal
instability, condensations start to occur at the loop top,
and fragment into smaller blobs moving downwards,
which are manifested as coronal rain shown in Figure 1.
Following coronal rain dynamics for more than 10 hr, we
carry out a statistical study of all coronal rain blobs toquantify their widths, lengths, areas, velocity
distributions, and other properties. The coronal rainshows us continuous heating–condensation cycles, aswell as cycles in EUV emissions. We also track themovement of individual blobs to study their dynamics
and the forces driving their movements. The blobs have aprominence-corona transition-region-like structure
surrounding them, and their movements are dominatedby the pressure evolution in the very dynamic loopsystem.
Besides the small-scale heating events, large scale
eruptions caused by the flux emergence could also
influence the development of coronal rain. By addingemerging flux at one footpoint of the coronal arcades, wealso investigate the eruptions caused by the emergenceand the response of coronal rain in the emerging
magnetic fields [2]. The emergence changes the pressurein the loops, and the internal coronal rain all moves tothe other side. The emerging flux reconnects with theoverlying magnetic field, forming a current sheet andmagnetic islands. The plasma is ejected outwards andheated, forming a cool jet ~6000 K and a hot X-ray jet~4 million Kelvin (MK) simultaneously. The jet
dynamical properties agree very well between
observation and simulation. In the simulation, the jet also
displays transverse oscillations with a period of 8
minutes, in a so-called whiplike motion. The movementof the jet and dense plasmoids changes the configurationof the local magnetic field, facilitating the occurrence ofthe Kelvin-Helmholtz instability, and vortex-likestructures form at the boundary of the jet. Our simulation
clearly demonstrates the effect of emergence on coronalrain, the dynamical details of reconnecting plasmoid
chains, the formation of multithermal jets, and thecycling of cool mass between the chromosphere and thecorona.
References[1] Li X., Keppens R., & Zhou Y., 2022, ApJ, 926, 216[2] Li X., Keppens R., & Zhou Y., 2023, ApJL, 947, L17

Figure 1. Snapshots at different times showing the evolution of coronal rain. The upper and lower panels display thenumber density and temperature respectively.