Punch hole cloud

The science behind the phenomenon. 

A fallstreak hole, also known as a hole punch cloud, punch hole cloud, skypunch, canal cloud or cloud hole, is a large circular or elliptical gap that can appear in cirrocumulus or altocumulus clouds. Such holes are formed when the water temperature in the clouds is below freezing but the water has not frozen yet due to the lack of ice nucleation (see supercooled water). When ice crystalsdo form it will set off a domino effect, due to the Bergeron process, causing the water droplets around the crystals to evaporate: this leaves a large, often circular, hole in the cloud.^[1]

It is believed that the introduction of large numbers of tiny ice crystals into the cloud layer sets off this domino effect of evaporation which creates the hole. The ice crystals can be formed by passing aircraft which often have a large reduction in pressure behind the wing- or propeller-tips. This cools the air very quickly, and can produce a ribbon of ice crystals trailing in the aircraft's wake. These ice crystals find themselves surrounded by droplets, grow quickly by the Bergeron process, causing the droplets to evaporate and creating a hole with brush-like streaks of ice crystals below it.