| A significant fraction of the precipitation that falls on Earth is formed by the collision-coalescence of cloud droplets, yet the rate of this process during the rain initiation stage is poorly understood. Recent studies have significantly advanced our understanding of the effects of in-cloud air turbulence on collisions between cloud droplets. Novel quantitative methods are currently being developed to better describe the turbulent enhancement of the gravitational collision-coalescence. This talk will review these recent developments and related challenges. An impact study based on kinetic collection equation using the most realistic collection kernel suggests that cloud turbulence can resolve the discrepancy between the observed time for rain initiation in warm convective clouds and the predicted time based on the gravitational mechanism alone. Results from a rising parcel model using several collection kernels for both continental and maritime clouds will also be discussed. |
|