Building a better raindrop

A new way to mathematically model raindrop formation in clouds may improve our understanding of Earth’s climate, cloud formation and movement, and the effect that small airborne particles have on rainfall. The first step in forming raindrops is called autoconversion, a process in which small droplets in a cloud combine to form larger drops. But to date, mathematical treatments of autoconversion have been oversimplified and vague because some of the terms in the equation lacked a physical basis. So Yangang Liu, Peter Daum, and Robert McGraw (all from Brookhaven National Laboratory) developed a new model for raindrop formation that takes into account the limited size range of droplets that can interact to create raindrops, the amount of liquid water present, and the concentration of droplets in a cloud. The atmospheric scientists say that their model not only is fully determined by the physics, with no tunable parameters, but is as...