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Lollipop-Shaped Ice Crystals In Clouds Have Scientists Curious

Clouds filled with ice lollipops — sounds like the chorus of a bubblegum pop song, or maybe a yummy treat to help keep cool in the summer. But, actually, it’s a phenomenon of nature that has scientists very curious.

Originally published on Nexus Media.
By Marlene Cimons

Clouds filled with ice lollipops — sounds like the chorus of a bubblegum pop song, or maybe a yummy treat to help keep cool in the summer. But, actually, it’s a phenomenon of nature that has scientists very curious.

Researchers discovered these lollipop-shaped crystals after scrutinizing more than 5 million images taken during a 2009 flight through a large cloud system in southwest England. The scientists used laser beam technology to capture the shapes of ice crystals as part of an effort to understand how ice forms at temperatures above -30 degrees Celsius.

They wanted to learn more about precipitation, the lifetime of clouds, and their reflectivity — all of which have an impact on weather and climate. They saw crystals with a very unusual shape, each a round circle of ice atop a “stick,” resembling a lollipop. Clouds were full of them, inspiring considerable scientific interest — and awe.

“Natural processes can create objects of real beauty,” said Jonathan Crosier, a senior research fellow who studies clouds at the University of Manchester, and one of the scientists involved in the work. “We instantly started asking ourselves questions about how they form.”

The researchers described their findings in a study published recently in Geophysical Research Letters, a journal of the American Geophysical Union. The authors include Crosier, Stavros Keppas, Keith Bower and T.W. Choularton, all of the University of Manchester.

This chart shows (a) the formation of an ice-lolly, (b) ice-lollies with spikes and (c) representations of ice-lollies observed at different temperatures. Source: Geophysical Research Letters

While previous research identified ice-lollies, this is the first time that these ice particles were seen in abundance, according to Crosier. Insights gained from studying them will provide important knowledge as to how clouds form and evolve.

For example, in any mixed-phase cloud (which is a cloud containing a mixture of super-cooled water and ice in close proximity) there is a very delicate balance between the liquid water and ice, he explained.

“Too much ice and the ice can consume the liquid water, which can lead to precipitation and the dissipation of the cloud,” he said. “Too little, and the ice will fall out, leaving behind a highly reflective super-cooled liquid cloud, which can persist for a long time, whilst generating virtually no precipitation.”

Many clouds lie somewhere in between, he said.

“Ice-lollies are a newly-identified ice particle which can alter the balance between liquid water and ice in mixed-phase clouds,” Crosier said. “Therefore, that may have a significant impact on cloud lifetime and precipitation formation.”

Scientists believe the process begins when ice crystals form at the top of a cloud system. Then, a warm stream of air blows through the cloud, carrying super-cooled — but still liquid — droplets of water. These droplets collide with the ice crystals and instantly freeze. Occasionally, tiny needles break off, fall through the cloud and hit more super-cooled droplets. These round drops stick to the top of the needle — and an ice-lolly is formed.

Ice-lolly formation. Source: Geophysical Research Letters

The ice-lollies tend to be between 0.25 mm and 1.5mm in length. They fall to the ground at around 3.6 kilometers per hour. “Since they were found at an altitude of around 4 kilometers, it would take just over an hour for them to reach the surface if they remain unchanged,” Crosier said. “However, when the air temperature increases above zero Celsius, then the lolly will melt and form a small rain drop.

“Even if the temperature profile of the atmosphere is negative — below zero Celcius — at all layers, ice-lollies might not reach the ground in their original shape, or be deformed due to other processes occurring in the clouds,” he said. And, if temperatures stay below zero Celsius, but humidity drops below 100 percent, “then the particles will start to sublimate and could vanish without a trace.”

Seeing these images has whetted the scientists’ imagination. They plan to continue studying ice-lollies to learn more about their origins. “The formation of part of the ice-lolly, the stick, is shrouded in mystery,” Crosier said. “Researchers have been trying to observe the freezing-shattering of small droplets for several decades, to no avail.”

“The evidence suggests that the process occurs in very specific conditions, not too hot and not too cold — just like Goldilocks’ porridge,” he added. “We are developing exciting new laboratory experiments to finally observe this fascinating, yet highly elusive process. This will help us to understand the fine detail on how ice-lollies form.”

A cartoon representation of ice-lolly formation. Source: JoAnna Wendel American Geophysical Union

Reprinted with permission.

 
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