  We present here one of the first high resolution spectroscopic observations
of coronal rain, performed with the CRISP instrument at the Swedish Solar
Telescope. This work constitutes the first attempt to assess the importance of
coronal rain in the understanding of the coronal magnetic field in active
regions. A large statistical set is obtained in which dynamics (total
velocities and accelerations), shapes (lengths and widths), trajectories
(angles of fall) and thermodynamic properties (temperatures) of the
condensations are derived. Specifically, we find that coronal rain is composed
of small and dense chromospheric cores with average widths and lengths of 310
km and 710 km respectively, average temperatures below 7000 K, displaying a
broad distribution of falling speeds with an average of 70 km/s and
accelerations largely below the effective gravity along loops. Through
estimates of the ion-neutral coupling in the blobs we show that coronal rain
acts as a tracer of the coronal magnetic field, thus supporting the
multi-strand loop scenario, and acts as a probe of the local thermodynamic
conditions in loops. We further find that the cooling in neighboring strands
occurs simultaneously in general suggesting a similar thermodynamic evolution
among strands, which can be explained by a common footpoint heating process.
Constraints for coronal heating models of loops are thus provided. Estimates of
the fraction of coronal volume with coronal rain give values between 7% and
30%. Estimates of the occurrence time of the phenomenon in loops set times
between 5 and 20 hours, implying that coronal rain may be a common phenomenon,
in agreement with the frequent observations of cool downflows in EUV lines. The
coronal mass drain rate in the form of coronal rain is estimated to be on the
order of 5x10^9 g/s, a significant quantity compared to the estimate of mass
flux into the corona from spicules.
