Coronal rain in randomly heated arcades

Abstract

Adopting the MPI-AMRVAC code, we present a 2.5-dimensional magnetohydrodynamic (MHD) simulation, which includes thermal conduction and radiative cooling, to investigate the formation and evolution of the coronal rain phenomenon. We perform the simulation in initially linear force-free magnetic fields which 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 rebound shocks are generated by the siphon inflows. Condensations fragment into smaller blobs moving downwards and as they hit the lower atmosphere, concurrent upflows are triggered. Larger clumps show us clear "coronal rain showers" as dark structures in synthetic EUV hot channels and bright blobs with cool cores in the 304 Å channel, well resembling real observations. Following coronal rain dynamics for more than 10 hours, we carry out a statistical study of all coronal rain blobs to quantify their widths, lengths, areas, velocity distributions, and other properties. The coronal rain shows us continuous heating-condensation cycles, as well as cycles in EUV emissions. Compared to previous studies adopting steady heating, the rain happens faster and in more erratic cycles. Although most blobs are falling downward, upward-moving blobs exist at basically every moment. We also track the movement of individual blobs to study their dynamics and the forces driving their movements. The blobs have a prominence-corona transition-region-like structure surrounding them, and their movements are dominated by the pressure evolution in the very dynamic loop system.

The influence of flux rope heating models on solar prominence formation

“…These mechanisms usually require the magnetic field topology local to the condensations to be concave upwards with respect to gravity; levitation against gravity is facilitated by means of the magnetic Lorentz force (pressure and tension), as first shown by the self-similar model of Kippenhahn and Schlüter (1957). Generally speaking, two main formation processes are discerned: (i) evaporationcondensation, where localised footpoint heating of a magnetic arcade produces upflows which collect in any preexisting dipped fields (Xia et al 2012(Xia et al , 2014Xia and Keppens 2016) -a theory shared with the phenomenon of coro-nal rain (Li et al 2021); and (ii) levitation-condensation Yokoyama 2015, 2018;Jenkins and Keppens 2021) or its variant reconnection-condensation (Kaneko and Yokoyama 2017), where a flux rope is dynamically formed through shearing and converging motions at lower altitudes -a sheared magnetic arcade, whose footpoints are subject to those motions, eventually changes internal connectivity via magnetic reconnection and builds a twisted, helical field (van Ballegooijen and Martens 1989). In doing so, the reconnection may redistribute or scoop up material from the chromosphere or lower corona, which remains suspended by the flux rope (levitation).…”

“…dipped fields (Xia et al 2012(Xia et al , 2014Xia and Keppens 2016) -a theory shared with the phenomenon of coronal rain (Li et al 2021); and (ii) the levitation-condensation model Yokoyama 2015, 2018;Jenkins and Keppens 2021) or its variant reconnection-condensation (Kaneko and Yokoyama 2017), where a flux rope is dynamically formed through shearing and converging motions at lower altitudes -a sheared magnetic arcade, whose footpoints are subject to those motions, eventually changes internal connectivity via magnetic reconnection and builds a twisted, helical field (van Ballegooijen and Martens 1989). In doing so, the reconnection may redistribute or scoop up material from the chromosphere or lower corona, which remains suspended by the flux rope (levitation).…”