Hole Punch Cloud Over Piberbach, Austria
March 08, 2011
This photo composite shows the development of a hole punch cloud and its attendant fall streak, during a time span of approximately twenty minutes, over Piberbach, Austria on August 17, 2008. Hole punch clouds can occur following cloud seeding, but they're almost always caused by aircraft passing through a shallow, mid-level cloud deck. They're not often seen but can be attention getting whenever they form. If the supercooled water droplets in the cloud layer are perturbed during a jet or propeller plane transit, the droplets will instantly freeze into myriad ice crystals. When this happens latent heat is released which warms the air and evaporates the undisturbed portion of the cloud. Ice crystals falling through the hole punch (the darkened patch near the center of the hole) are called fall streaks. These crystals almost always sublimate before reaching the surface.
Photo details: Canon EOS 300D camera; Tokina 28-300 mm zoom lens (in program mode); 1/500 to 1/640 second exposure; f/11 to f/16 aperature; ISO 400. The individual images were taken at 6:57, 7:07, 7:13 and 7:17 p.m. on August 17, 2008.