Self-consistent 3D radiative magnetohydrodynamic simulations of coronal rain formation and evolution

Abstract

<jats:p><jats:italic>Context.</jats:italic> Coronal rain consists of cool and dense plasma condensations formed in coronal loops as a result of thermal instability.</jats:p> <jats:p><jats:italic>Aims.</jats:italic> Previous numerical simulations of thermal instability and coronal rain formation have relied on the practice of artificially adding a coronal heating term to the energy equation. To reproduce large-scale characteristics of the corona, the use of more realistic coronal heating prescription is necessary.</jats:p> <jats:p><jats:italic>Methods.</jats:italic> We analysed coronal rain formation and evolution in a three-dimensional radiative magnetohydrodynamic simulation spanning from convection zone to corona which is self-consistently heated by magnetic field braiding as a result of convective motions.</jats:p> <jats:p><jats:italic>Results.</jats:italic> We investigate the spatial and temporal evolution of energy dissipation along coronal loops which become thermally unstable. Ohmic dissipation in the model leads to the heating events capable of inducing sufficient chromospheric evaporation into the loop to trigger thermal instability and condensation formation. The cooling of the thermally unstable plasma occurs on timescales that are comparable to the duration of the individual impulsive heating events. The impulsive heating has sufficient duration to trigger thermal instability in the loop but does not last long enough to lead to coronal rain limit cycles. We show that condensations can either survive and fall into the chromosphere or be destroyed by strong bursts of Joule heating associated with a magnetic reconnection events. In addition, we find that condensations can also form along open magnetic field lines.</jats:p> <jats:p><jats:italic>Conclusions.</jats:italic> We modelled, for the first time, coronal rain formation in a self-consistent 3D radiative magnetohydrodynamic simulation, in which the heating occurs mainly through the braiding and subsequent Ohmic dissipation of the magnetic field. The heating is stratified enough and lasts for long enough along specific field lines to produce the necessary chromospheric evaporation that triggers thermal instability in the corona.</jats:p>

Excitation and evolution of coronal oscillations in self-consistent 3D radiative MHD simulations of the solar atmosphere

“…After inserting the magnetic field into the domain, it is quickly swept around by convective motions. These lead to magnetic field braiding and associated Ohmic and viscous heating which together maintain high temperature in the chromosphere and corona (see e.g., Carlsson et al 2016;Kohutova et al 2020a for further details of the numerical setup).…”

“…We note that the simulation does not include magnetic flux emergence which means the loops are not mass loaded and pushed into the corona from the lower solar atmosphere. Instead, the dense loops are filled via chromospheric evaporation caused by localised heating (Kohutova et al 2020a). However, some transverse structuring is still present thanks to the temperature variation across different magnetic field lines.…”

“…Therefore, in order to investigate the oscillatory behaviour of coronal loops in the simulation, it is necessary to trace the evolution of the corresponding magnetic field lines through both time and space. To do this, we use a fieldtracing method previously used by Leenaarts & Carlsson (2015) and Kohutova et al (2020a). A magnetic field line is defined as a curve in 3D space r(s) parametrised by the arc length along the curve s, for which dr/ds = B/|B|.…”

A fast multi-dimensional magnetohydrodynamic formulation of the transition region adaptive conduction (TRAC) method

“…Obtaining this spatial resolution in active-region-sized 3D MHD models poses a serious challenge (e.g. Reid et al 2018Reid et al , 2020Knizhnik et al 2019;Kohutova et al 2020), for simulations to be run in a realistic time.…”

When hot meets cold: post-flare coronal rain

“…Coronal rain is also observed in non-flaring coronal loops, is frequently found in loops of active regions [15,16,17,18,19,20,21], and this type of coronal rain has been studied previously using magnetohydrodynamic (MHD) simulations [22,23,24,25,26]. It has been generally accepted that these rain blobs are generated in a catastrophic cooling process, essentially caused by thermal instability [27,28,29,30].…”