  A simple theory, based on observations of snowflake distribution in a
turbulent flow, is proposed to model the growth of inertial particles as a
result of dynamic clustering at scales larger than the Kolmogorov length scale.
Particles able to stick or coalesce are expected to grow in size in flow
regions where preferential concentration is predicted by a critical Stokes
number $St=\tau_p/\tau_f \simeq 1 $. We postulate that, during growth, $St$
remains critical, with the particle response time $\tau_p$ evolving according
to the specific flow time scale $\tau_f$ defined by the vortices around which
progressively larger particles end up orbiting. This mechanism leads to the
prediction of the limiting size of aggregating particles in a turbulent flow.
Such limit is determined by the extent of the turbulent inertial range, which
can be formulated as a function of accessible integral-scale quantities. The
proposed dynamically critical Stokes growth provides a framework to interpret
particle aggregation, size growth and particle cluster growth in various
geophysical multi-phase flows.
