Hole Punch and Fall Streak Over Grimsby, U.K.

May 11, 2011

Photographer: Robert Chase
Summary Author: Cloud Appreciation Society; Jim Foster

The photo above shows a superb example of a hole punch and fall streak as observed over Grimsby, U.K., on the east coast of England. The almond-shaped tear in this altostratus cloud deck likely resulted from an aircraft transit. When supercooled cloud water droplets are disturbed by a plane or jet, they’re instantly crystallized. As this occurs, latent heat is released, and the undisturbed portion of the cloud, near the initial perforation, evaporates. The feathery wisps in the “tear” are composed of ice crystals and referred to as fall streaks. They may appear to be trying to fill the rip in the cloud fabric, but they’re simply descending through a hole of opportunity. Even though these crystals are falling, they rarely reach the surface since they quickly sublimate in the drier air immediately below the cloud deck.

Note the subtle iridescence, particularly along the edges of the clouds. The tiny cloud droplets are of the proper size to deflect sunlight. Droplets tend to be more uniform along the rims of altostratus or altocumulus clouds and display the most noticeable coloration.

Photo details: Camera Maker: Panasonic; Camera Model: DMC-FZ38; Focal Length: 4.8mm (35mm equivalent: 27mm); Aperture: f/8.0; Exposure Time: 0.0025 s (1/400); ISO equiv: 80; Exposure Bias: none;
Metering Mode: Matrix; Exposure: program (Auto); White Balance: Auto; Flash Fired: No (enforced); Orientation: Normal; Color Space: sRGB.