Scientists have witnessed the birth of an ice cloud for the first time
This is where clouds come from.
PETER DOCKRILL
21 DEC 2016
ice crystals on individual atmospheric particles, giving an unprecedented glimpse at the way
ice clouds form in our atmosphere.
The process, called
ice nucleation, occurs when a particle attracts water vapour and forms ice crystals, which become the core of the wispy cirrus clouds that often hang in the sky above our heads. Observing this microscopic chain of events first-hand isn't easy, but it's vital for our understanding of how clouds take shape and both cool and heat the planet.
"This is one of the most critical but least understood parts of the process of how cold clouds form,"
said one of the team. Bingbing Wang, from the Pacific Northwest National Laboratory.
"The fundamental process of how ice grows is relatively well understood, but ice nucleation – that moment when the first group of molecules comes together – remains a big challenge."
Ice crystals forming around the kaolinite particle in the very first seconds of the formation of an ice cloud. Credit: Pacific Northwest National Laboratory
To recreate the process in the lab, the team had to replicate conditions found high above Earth's surface – at an altitude of about 6 kilometres (20,000 feet), where cirrus clouds form in the sky.
At this height, relative humidity is high and temperatures are very low, meaning water vapour readily collects on any small particles floating in the atmosphere, before freezing in place as an ice deposit.
In the atmosphere, such airborne particles could be almost anything, including volcanic ash, aircraft emissions, or even microbes.