Every Raindrop is Exceptional

Rainfall from ice-free cumulus clouds requires collisions of very large numbers of microscopic droplets to create every raindrop, and the collision rate for the first few droplet coalescences is typically less than one per hour. The onset of rain showers can be surprisingly rapid, much faster than the mean time required for a single collision. The explanation is that every raindrop is the result of a sequence of exceptionally rare events, where the first few collisions happen unusually quickly.

The talk will discuss how large-deviation theory and extreme value statistics can give a quantitative description of rainfall, including recent results on the growth history of those 'lucky' microscopic droplets which grow to become raindrops.