Thursday, April 5, 2012




This is a rare meteorological phenomenon called a skypunch. Ice crystals form above the high-altitude cirro-cumulo-stratus clouds, then fall downward, punching a hole in the cloud cover.


A fallstreak hole, also known as a hole punch cloud, punch hole cloud, canal cloud or cloud hole, is a large circular 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 particles (see supercooled water). When a portion of the water does start to freeze it will set off a domino effect, due to the Bergeron process, causing the water vapour around it to freeze and fall to the earth as well. This leaves a large, often circular, hole in the cloud.

It is believed that a disruption in the stability of the cloud layer, such as that caused by a passing jet, may induce the domino process of evaporation which creates the hole. Such clouds are not unique to any one geographic area and have been photographed from the United States to Russia.

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