Abstract |
In solar coronal loops, thermal non-equilibrium (TNE) is a phenomenon that can occur when the heating is both highly-stratified (i.e. mainly concentrated at the loops footpoints) and quasi-constant. It is resulting in a particular response of the plasma: evaporation and condensation cycles with periodic evolution of the temperature and the density.
TNE processes (thermal instability) are known to play an important role in prominences and coronal rain, i.e. in the formation of plasma about 100 times denser and 100 times cooler than the surrounding coronal plasma. In the case of coronal rain, the condensations cool down to chromospheric temperature and fall down toward the loop legs. Understanding the characteristics of thermal nonequilibrium cycles is essential to understand the circulation of mass and energy in the corona.
The long-period intensity pulsations reported by Auchere et al. (2014) are very common in the solar corona and especially in coronal loops. Recently, these pulsations have been identified as the coronal counterpart of thermal nonequilibrium cycles (evaporation and condensations) by Froment et al. (2015, 2017).
Here, we report the first combined observations of long-period (6 hours) intensity pulsations in the coronal channels of SDO/AIA and coronal rain with the CRISP and CHROMIS instruments at the Swedish 1-m Solar Telescope (SST) in the same coronal loop bundle. The high-resolution spectroscopic instruments at the SST allowed us to probe the cooling phase of one of the cycles, down to chromospheric temperatures. These current observations are focused on one footpoint of the observed loop bundle and reveal the fine-structured rain strands. We present the thermal analysis of the cycles with the channels of AIA (DEM, time-lag analysis) on three days of off-limb evolution. Further, we also report statistics on the coronal rain blobs that we derive from CRISP and CHROMIS data (temperature, velocities, density, sizes of the blobs).
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