(Top) Photograph of aircraft-induced hole observed on 29 January 2007. (Bottom) A computer simulation of hole formation in a cloud. Adding ice to a supercooled cloud results in rapid ice crystal formation. This ice falls to the ground as snow, leaving behind a hole.
Credit: Jafvis / A. Heymsfield et al.
Aircraft-induced hole observed in Antarctica on 12 Dec 2009. It is likely that a Lockheed LC-130 aircraft produced the ice that formed the hole.
Credit: Eric Zrubek and Michael Carmody
SHROPSHIRE: Aeroplanes passing through the atmosphere are creating holes in the clouds which can cause disruptive weather, say researchers.
In a study published in the current issue of Science, researchers explain how cloud holes are created when part of the cloud freezes and falls to the ground as snow - a process that can be triggered by an aircraft.
The result is otherworldly: a spectacular 'hole-punch cloud' above Moscow in 2009 prompted murmurings of alien invasions and Russian weather weapons.
"We examined how frequently cloud holes occur near several major airports", said lead author Andrew Heymsfield from the National Centre for Atmospheric Research in Colorado, U.S. "We show an example where this process produced a snowfall rate of 2 inches (5 cm) per hour. Snow near and around airports has effects on airport traffic and de-icing operations."
How to make a holey cloud
There are two key ingredients required for the creation of a holey cloud: supercooled water and a sudden temperature drop.
Supercooled water seems to defy the laws of physics by remaining liquid at sub-zero temperatures. This phenomenon occurs in clouds at temperatures between 0 and -40°C when there are no ice nuclei (e.g. dust particles) present to allow the water droplets to crystallise.
However, a sudden drop in cloud temperature may help to initiate ice crystal formation. An aircraft can provide this cooling via an expansion of air behind the propeller tips or by airflow over the wings.
The introduction of ice into a supercooled cloud triggers a domino effect of rapid ice formation. When the ice becomes too heavy to remain in the cloud, it falls to the ground as snow, leaving behind a void.
Hole spotting
The method by which ice crystals grow in a supercooled cloud is known as the Bergeron-Findeisen (B-F) process, in which water droplets evaporate, condense and freeze onto the ice crystals, leading to further crystal growth. However, the B-F process is unlikely to provide the whole story.
Andrew Heymsfield and colleagues studied satellite images of a holey cloud layer over Texas, taken by the Geostationary Operational Environmental Satellite (GOES) on 29 January 2007.
In total, 92 holes were spotted, produced by a wide variety of aircraft, including large passenger jets, military jets and turboprop aeroplanes. A typical hole grew for an hour after it was first detected, up to a maximum length of over 100 km in some cases. Several holes remained in the sky for more than four hours.
Aeroplanes
Airplanes have not been called "aeroplanes" for a long time. This article is totally ridiculous. Did you guys run out of interesting things to talk about? Just trying to fill space or what?