Four individual raindrops hitting their highest peaks could easily end up thousands of miles apart, one flowing north to the Beaufort Sea, another reaching the the Gulf of Mexico, a third would be absorbed into Hudson Bay to the east and the last into the vast Pacific.

The raindrops that patter onto roofs, sidewalks and umbrellas during a shower or storm fall in a wide range of sizes, as anyone who pays attention can see. The explanation for this variety turns out to be much simpler than scientists thought.

Experts have long thought that the size differences observed in natural raindrops was due to the same complex interactions of droplets that form raindrops in clouds. But a new study finds that the best explanation for the motley size assortment is that the raindrops released from the clouds break up into smaller drops as they fall.

Rain forms in clouds as water vapor gloms onto dust or other tiny particles, gradually building up. Because these infant drops are relatively packed together in the cloud, they collide with one another and coalesce into larger drops. The turbulent air inside a storm cloud can aide the process.

It was presumed that this same process of collision kept up on the fall to the ground, resulting in some drops being bigger or smaller than others.

But a team of French scientists had another idea.

For the collision proposal to work, the falling raindrops would have to be close enough to collide frequently enough and they would need enough time to do so, Emmanuel Villermaux and Benjamin Bossa, both of Aix-Marseille Université, wrote in their study, which is detailed online on July 20 in the journal Nature Physics. They consider these conditions "unlikely."

Instead, by analyzing high-speed movies of falling water droplets, Villermaux and Bossa found that the drops go through a series of shape-shifting moves and finally burst apart into a spray of multi-sized drops.