Effects of Turbulence on the Coagulational Growth of Cloud Droplets: An Overview and Recent Results (Keynote)

Although the importance of turbulence on rain formation was noted at least 60 years ago, progress has been very slow in quantifying the turbulence effects [1]. Adequate treatment of the turbulence effects on droplet growth represents a major gap in our understanding of cloud microphysical processes [2–7]. In this talk, we will discuss open issues in this subject, and report on an on-going, systematic effort to address various effects of turbulence on the growth of small cloud droplets to sizes for which the gravitational coagulation can operate effectively. We focus on the evolution in the size range from 10 μm to 100 μm for which the condensational growth is no longer an effective growth mechanism and gravitational coagulation alone is not sufficient to grow droplets at a rate typically observed. This size range involves a change of droplet inertial response time by roughly two orders of magnitude.