Coronal rain in magnetic bipolar weak fields

Abstract

Aims. We intend to investigate the underlying physics for the coronal rain phenomenon in a representative bipolar magnetic field, including the formation and the dynamics of coronal rain blobs. Methods. With the MPI-AMRVAC code, we performed three dimensional radiative magnetohydrodynamic (MHD) simulation with strong heating localized on footpoints of magnetic loops after a relaxation to quiet solar atmosphere. Results. Progressive cooling and in-situ condensation starts at the loop top due to radiative thermal instability. The first large-scale condensation on the loop top suffers Rayleigh-Taylor instability and becomes fragmented into smaller blobs. The blobs fall vertically dragging magnetic loops until they reach low-β regions and start to fall along the loops from loop top to loop footpoints. A statistic study of the coronal rain blobs finds that small blobs with masses of less than 10 10 g dominate the population. When blobs fall to lower regions along the magnetic loops, they are stretched and develop a non-uniform velocity pattern with an anti-parallel shearing pattern seen to develop along the central axis of the blobs. Synthetic images of simulated coronal rain with Solar Dynamics Observatory Atmospheric Imaging Assembly well resemble real observations presenting dark falling clumps in hot channels and bright rain blobs in a cool channel. We also find density inhomogeneities during a coronal rain "shower", which reflects the observed multi-stranded nature of coronal rain.

In Situ Generation of Transverse Magnetohydrodynamic Waves from Colliding Flows in the Solar Corona

“…legs of prominences (Vial & Engvold 2015). These longitudinal dynamics are commonly associated to the formation mechanism of prominences or coronal rain, such as thermal instability or thermal non-equilibrium (Antiochos et al 1999;Karpen et al 2001;Antolin et al 2010;Xia et al 2017 Pesnell et al 2012), and numerical MHD modelling ( §4), we show that in-situ collisions from such counter-streaming flows could be a source of transverse MHD waves in the corona.…”

Impact of Type II Spicules in the Corona: Simulations and Synthetic Observables

“…The results presented here and in Martinez-Sykora et al (2017) are of great interest for further studies since they provide constraints for ad hoc terms that other models use, e.g., episodic heating profiles as a function of height for coronal rain simulations such as (Antolin et al 2010;Xia et al 2017), or wave amplitudes and fluxes for waves studies . The heating profile shown in Figure 6 could be used as input/driver for many other studies.…”

Spectroscopic detection of coronal plasma flows in loops undergoing thermal non-equilibrium cycles

“…Coronal rain has long been observed in chromospheric and transition region spectral lines, forming blobs-like structures which appear to fall along coronal loops (Kawaguchi 1970;Leroy 1972;Foukal 1978;Schrijver 2001;De Groof et al 2004;De Groof et al 2005;O'Shea et al 2007;Antolin et al 2010;Antolin & Rouppe van der Voort 2012;Vashalomidze et al 2015). The formation and dynamics of coronal rain is reproduced with simulations of TNE, both in 1D simulations mentioned above, in 2.5D (Fang et al 2013 and in 3D (Moschou et al 2015;Xia et al 2017). Coronal rain may also be observed in post-flare loops, where the plasma evaporates and catastrophically cools as a result of the intense transient heating from the flare (Scullion et al 2016).…”

“…The reference region used to correct the orbital drift therefore includes the pulsating loops, which could slightly attenuate the velocity variations. The presence of counter-streaming flows (Fang et al 2013Xia et al 2017) may further explain the small velocity variations. Such flows would indeed add a blueshifted contribution to the spectral line, which would shift its centroid towards lower velocities.…”

“…In addition to the periodic flows of plasma at coronal temperatures, multidimensional simulations by Fang et al (2013Fang et al ( , 2015 and Xia et al (2017) predict that coronal rain should be accompanied by simultaneous counter-streaming flows occurring in adjacent field lines. If such flows occur at coronal temperatures, they should result in a periodic broadening of the spectral lines during the TNE cycles.…”