Scientists had assumed that the scattered size distribution of raindrops hitting the ground resulted from collisions with their neighbours, just like those in clouds. But Emmanuel Villermaux and Benjamin Bossa at the Aix-Marseille University in France determined that the key to this phenomenon is the dynamics of individual drops.
A high-speed camera captured the moment when a single drop fell through the air, flattening like a pancake as it neared terminal velocity. It then inflated into a bag-like shape before splitting into stringy filaments and, finally, bursting into a shower of different-sized droplets (pictured).
The complete metamorphosis from drop to droplets occurred more quickly than the typical collision time between drops in clouds.
For a longer story on this research see http://tinyurl.com/kop4ww