This project will improve our understanding of the way raindrops grow and interact with each other to produce a broad range of drop sizes. Some collisions between drops lead to simple coalescence and the formation of a larger drop; others may cause breakup of the colliding drops and the production of smaller, satellite droplets. A mathematical formulation of this problem requires knowledge of the fall speeds and collision cross sections of drops of different sizes, the probability of breakup, and the size distribution of the satellite droplets. The first phase of the project will provide analytical approximations to the sparse existing laboratory data on drop breakup. This is essential for generalizing the equations that describe the evolution of the drop-size distribution by the collision-coalescence process to include the effects of drop breakup. The second phase will compare model predictions with the drop-size distributions measured by Doppler radar in natural clouds. If the predictions agree with observations it will support the use of the model in theoretical calculations of rain development under different environmental conditions.
