Xiang-Yu Li, PhD student at MISU/Nordita/KTH
Xiang-Yu Li, PhD student at MISU/Nordita/KTH

Xiang-Yu Li

Nordita, KTH & Stockholm University 
Department of Meteorology, Stockholm University, Sweden


Bottleneck problem of cloud droplet growth is one of the most challenging problems for cloud physics. Cloud droplet growth is neither dominated by condensation nor gravitational coagulation in the size range of 15 μm ∼ 50 μm. Turbulence-generated coagulation is argued to be the mechanism to cause the size gap.

The seminar presents a study that investigates the turbulence effect on coagulational growth of cloud droplet. We found that the coagulation rate strongly depends on the small-scale properties of turbulence. The coagulation is enhanced with increasing energy dissipation rate. Clustering of particles is weakened with increasing energy dissipation rate and caustics is enhanced. This is due to the fact that larger energy dissipation results in a wider range of Stokes number, therefore, weakening the clustering and strengthening the caustics. When coagulation is invoked, the system becomes non-equilibrium with Stokes number as a function of time and space, in which caustics dominates the coagulational growth.