Fallstreak hole: How this rare cloud formation was made

Residents of Gippsland in Victoria, Australia were astonished to see what looked liked a giant hole appear in the clouds above yesterday.

The phenomenon, which is known as a fallstreak hole or hole punch cloud, occurs when water droplets in the cloud start to freeze into ice crystals, become heavier and subsequently drop below the formation.

Fallstreak holes usually appear in cirrocumulus or altocumulus clouds and when a small group of droplets start to drop in temperature, a domino-like effect called the Wegener–Bergeron–Findeisen process, and freezes other droplets around it.

It's not exactly clear what causes the phenomenon, but according to an article in the journal Science, one theory is that as aircraft pass through the formations, cold air flows over the propeller tips and starts the process.

In 2012, a fallstreak hole was seen above Derbyshire and Leicestershire, near East Midlands airport. Others have been spotted in Moscow and Romania in recent years.

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