Environmental & Climate Sciences Department Seminar

The cloud droplet 'growth gap' problem in warm rain formation has troubled the cloud physics community for a few decades now. Turbulence has been considered as one of the mechanisms to overcome this bottleneck between cloud droplet growth by diffusion and growth by collision-coalescence. Being able to better understand and predict droplet growth rates would mean better estimates of cloud properties such as lifetime, precipitation, albedo etc. In this study, we use digital in-line holography to obtain volume measurements of cloud droplets with sizes near this growth gap in a turbulent laboratory chamber. We find that turbulent fluctuations in droplet number concentrations may lead to fluctuations in local supersaturation. Droplet growth through this stochastic condensation process results in broader droplet size distributions with some droplets growing large enough to jump the growth gap. We find similar results for airborne measurements of warm clouds suggesting this process should occur in the atmosphere as well. This approach is then extended to mixed phase clouds, and our first results show the importance of aerosol properties in controlling cloud glaciation.