An exploration of cloud droplet growth by condensation and collision-coalescence in a convection-cloud chamber

Atmospheric clouds are crucial to weather and climate, and the rate at which droplets collide and coalesce to form precipitation is one of the fundamental controlling processes. The convection-cloud chamber allows the interactions between aerosols and cloud droplets produced by condensation to be investigated within a turbulent environment. Studying the full range of microphysical conditions in atmospheric clouds is not possible, however, unless conditions for droplet growth by collision and coalescence are also achieved. In this study, we explore the conditions favorable to collision-coalescence growth in convection-cloud chambers, extending previous work on steady-state droplet size distributions due to condensation alone. We obtain analytic expressions for cloud droplet collision-coalescence rates, and for the functional form of droplet size distributions themselves. We derive several scaling laws and demonstrate consistency between these theoretical results and Monte-Carlo simulations of growth and precipitation within a convection-cloud chamber. Finally, we gain insights into the role of external parameters such as injection rate, supersaturation forcing, and chamber height in controlling the strength of the collision-coalescence process, and the resulting shape of the droplet size distribution