A cloud full of ice lollies sounds like something out of a fairy tale. But this phenomenon has been spotted in cloud systems over the UK and North Atlantic.

A significant concentration of these curious ice formations – in the shape of a stick with a spherical head at the end – were seen on a research flight over the north-east Atlantic Ocean last September, after previously being observed over the south-west UK in January 2009. and his colleagues at the University of Manchester have now published their findings from both flights.

The observations made in 2009 were more comprehensive, as measurements from the aircraft’s on-board probes were combined with data from a radar system in the southern UK. There was no radar coverage in 2016 because the sighting was in a relatively remote region.

The ice lollies seen in 2009 were typically about a millimetre long and found at an altitude of between 1 and 2.3 kilometres. They formed when a belt of rising humid air moving through clouds generated supercooled water droplets that collided with stick-shaped ice particles falling from the top of the clouds – created by the splintering and accretion of frozen water.

“More measurements are needed in this region of a cloud system to see if this is a widespread phenomenon,” says Keppas. However, he thinks these ice lollies form on a regular basis, especially at high latitudes. There is a good chance of finding more now that some of the cloud regions in which they form are known about, he says.

Ice lollies can alter the balance between liquid water and ice in clouds, which may have an impact on the clouds’ lifetime and thus their reflectivity, says Keppas. They could also potentially affect the formation of precipitation.

at the Catholic University of Louvain (UCL) in Belgium, says the lollies are “interesting features” and help shed light on the processes active in clouds. But he says the limited number of sightings so far prevents us from assessing their possible importance in the climate system.

Recent advances in measurement techniques allow us to see meteorological phenomena with increasing precision. Tiny formations in large cloud systems are now easier to spot, says Docquier.

“This is a nice and unique data set showing us again the complexity of the nature of clouds,” says at Stony Brook University in New York. “Usually one observes many small droplets attached to an ice crystal during such events and not one larger droplet attached to the end of the crystal.”

It would be interesting to know whether similar ice formations could occur in “atmospheric river” events associated with heavy precipitation on the US west coast, he adds.

Journal reference: Geophysical Research Letters, DOI:

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