  We investigate the properties of cool cores in an optimally selected sample
of 37 massive and X-ray-bright galaxy clusters, with regular morphologies,
observed with Chandra. We measured the density, temperature, and abundance
radial profiles of their intracluster medium (ICM). From these independent
quantities, we computed the cooling (tcool) free-fall (tff), and turbulence
(teddy) timescales as a function of radius. By requiring the profile-crossing
condition, tcool=teddy=1, we measured the cool-core condensation radius Rccc,
within which the balancing feeding and feedback processes generate the
turbulent condensation rain and related chaotic cold accretion (CCA). We also
constrained the complementary (quenched) cooling flow radius Rqcf, obtained via
the condition tcool=25Xtff, that encompasses the region of thermally unstable
cooling. We find that in our cluster sample and in the limited redshift range
considered (1.3E14<M500<16.6E14 Msun, 0.03<z<0.29), the distribution of Rccc
peaks at 0.01r500 and the entire range remains below 0.07r500, with a very weak
increase with redshift and no dependence on the cluster mass. We find that Rqcf
is typically 3 times larger than Rccc, with a wider distribution, and growing
more slowly along Rccc, according to an average relation Rqcf~Rccc^(0.46), with
a large intrinsic scatter. We suggest that this sublinear relation can be
understood as an effect of the micro rain of pockets of cooled gas flickering
in the turbulent ICM, whose dynamical and thermodynamical properties are
referred to as "macro weather". Substituting the classical cool-core radius
R(7.7Gyr), we propose that Rqcf is an indicator of the size of the global cores
tied to the long-term macro weather, with the inner Rccc closely tracing the
effective condensation rain and chaotic cold accretion (CCA) zone that feeds
the central supermassive black hole.

Astrophysics of Galaxies