A fat raindrop lands and splish – it bursts open on your nose. How did it become heavy enough to fall from the sky? Some clouds struggle to release their liquid load; others produce downpours with ease. Scientists have for the first time observed raindrops in their early growth phase and can confirm that turbulent air currents help droplets cluster and grow.
Using a plane with a 3D imaging system mounted under its wing, the researchers were able to show that turbulent currents inside a cloud helped midsize droplets cluster, increasing the chances of them colliding and creating a bigger drop.
Most clouds start with tiny droplets of about 15μm diameter, which need to grow to 100μm before they can fall as rain. Neither condensation nor gravity is enough to start the process. The images prove the random churning from turbulence creates crowds of droplets, triggering the embryonic growth phase.
The findings, published in the Physics Review Letters journal, suggest highly turbulent clouds are the most effective rainmakers.
