cavum
A cavum, or hole-punch cloud, is a large gap, usually circular or elliptical, that can appear in cirrocumulus or altocumulus clouds. These formations occur when part of a cloud with supercooled water droplets freezes into ice crystals owing to inadvertent seeding by aircraft flying through clouds at temperatures below about −10° to −20°C, even without sufficient ice nuclei, due to cooling as air expands over the wings or propellers.
Term updated 24 April 2017.
