Long Hole Punch
August 23, 2010
On the morning of 30th July 2010, I was walking across the Old Dominion University campus in Norfolk, Virginia and couldn’t help but notice a very long “hole punch” with a delicate cirrus “feather” inside it. Unfortunately, I did not have a wide angle lens with me and was therefore only able to capture about two thirds of the initial display. I could see no evidence of fall streaks, and about 20 minutes later the whole thing had dissipated. The passage of commercial aircraft through super-cooled altocumulus and altostratus clouds can induce freezing of droplets and subsequently, holes and channels in a cloud layer. Distrails (or "anti-contrails") can also produce linear voids, but it’s believed that hole punch clouds are not generally produced by this process. Several different mechanisms are suspected of widening these holes and channels over time including: dispersion of the aircraft’s exhaust trail, evaporation of droplets at the edges of the hole, and latent heating from ice growth, which raises the temperature within the hole.
Photo details: Camera Maker: OLYMPUS IMAGING CORP; Camera Model: SP570UZ; Focal Length: 4.6mm; Aperture: f/5.6; Exposure Time: 0.0020 s (1/500); ISO equiv: 64; Exposure Bias: none; Metering Mode: Matrix; Exposure: Creative Program (based towards depth of field); White Balance: Auto; Flash Fired: No; Color Space: sRGB.