什么是 Warm-rain process; ice-crystal process？

In the warm-rain process, the larger droplets of a cloud fall faster than the small ones, collide with them and merge, growing as they fall. In the ice-crystal process, in the part of a cloud colder than $0{}^{\circ}\mathrm{C}$ where ice crystals and supercooled droplets (liquid below $0{}^{\circ}\mathrm{C}$) are mixed, the crystals grow by taking the vapour that the droplets evaporate; they fall as snowflakes, and melt into raindrops if the air below is warm.