P. Antolin, M. Carlsson, L. Rouppe van der Voort, E. Verwichte, G. Vissers
The tropical wisdom that when it is hot and dense we can expect rain might
also apply to the Sun. Indeed, observations and numerical simulations have
shown that strong heating at footpoints of loops, as is the case for active
regions, puts their coronae out of thermal equilibrium, which can lead to a
phenomenon known as catastrophic cooling. Following local pressure loss in the
corona, hot plasma locally condenses in these loops and dramatically cools down
to chromospheric temperatures. These blobs become bright in H-alpha and Ca II H
in time scales of minutes, and their dynamics seem to be subject more to
internal pressure changes in the loop rather than to gravity. They thus become
trackers of the magnetic field, which results in the spectacular coronal rain
that is observed falling down coronal loops. In this work we report on high
resolution observations of coronal rain with the Solar Optical Telescope (SOT)
on Hinode and CRISP at the Swedish Solar Telescope (SST). A statistical study
is performed in which properties such as velocities and accelerations of
coronal rain are derived. We show how this phenomenon can constitute a
diagnostic tool for the internal physical conditions inside loops. Furthermore,
we analyze transverse oscillations of strand-like condensations composing
coronal rain falling in a loop, and discuss the possible nature of the wave.
This points to the important role that coronal rain can play in the fields of
coronal heating and coronal seismology.
View original:
http://arxiv.org/abs/1202.0787
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