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Coronal rain in magnetic bipolar weak fields
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. 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. 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 beta 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.Comment: 8 figure
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