8 June 2017
By JoAnna Wendel
A cloud full of lollipops may sound like the most delicious carnival treat ever… except this cloud’s lollipops are made of ice. Scientists spotted the lollipop-shaped ice crystals during a research flight in southwest England. The researchers describe their findings in a new study in Geophysical Research Letters, a journal of the American Geophysical Union.
The researchers, from the University of Manchester in the United Kingdom, flew through a large cloud system in 2009 to better understand how ice forms at relatively mild temperatures (warmer than minus 30 degrees Celsius). Pure water freezes at around minus 38 degrees Celsius, so scientists want to understand the formation of ice in clouds warmer than this temperature. That information would help them understand processes like precipitation formation, cloud lifetime, and cloud reflectivity.
One of the research plane’s instruments uses laser beams to detect the crystals’ shapes as the plane soars through the clouds. After digging through their data, the researchers realized that some of these crystals had a distinct shape—a circle of ice atop a long, columnar “needle.” They deemed these crystals “ice lollies.”
By studying where the ice lollies appeared and using past research about ice particle formation, the researchers figured out the ice lollies’ chilly origins. First, crystals of ice form at the coolest tops of a cloud system. A warm stream of air blows through the cloud like a conveyor belt, carrying with it super-cooled droplets of water—that’s water colder than 0 degrees Celsius but still a liquid. These super-cooled drops collide with the ice crystals, instantly freezing. Sometimes, tiny needles break off in the collision. Those needles fall through the cloud and collide with more super-cooled droplets. These round droplets fuse to the top of the needle—like a lollipop top connecting to a stick.
— JoAnna Wendel is a staff writer at Eos. Follow her on twitter at @JoAnnaScience.