Turbulence-induced cloud voids: observation and interpretation

Karpińska K., Bodenschatz J.F.E., Malinowski S.P., Nowak J.L., Risius S., Schmeissner T., Shaw R.A., Siebert H., Xi H., Xu H., and Bodenschatz E.

Atmospheric Chemistry and Physics

19, 2019, 4991-5003, 10.5194/acp-19-4991-2019

The phenomenon of "cloud voids", i.e., elongated volumes inside a cloud that are devoid of droplets, was observed with laser sheet photography in clouds at a mountain-top station. Two experimental cases, similar in turbulence conditions yet with diverse droplet size distributions and cloud void prevalence, are reported. A theoretical explanation is proposed based on the study of heavy inertial sedimenting particles inside a Burgers vortex. A general conclusion regarding void appearance is drawn from theoretical analysis. Numerical simulations of polydisperse droplet motion with realistic vortex parameters and Mie scattering visual effects accounted for can explain the presence of voids with sizes similar to that of the observed ones. Clustering and segregation effects in a vortex tube are discussed for reasonable cloud conditions.