Hole Punch Clouds and Sundog Over Southern England

October 24, 2016

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Photographer: Helga Parker
Summary Authors: Greg Parker; Jim Foster

Show above are photos featuring several hole punch clouds and an eye-catching sundog (top photo) as observed over the New Forest Observatory in southern England (Hampshire). My wife and I noticed this exceptional sky as we were taking our dog for a morning walk. Hole punch clouds are nearly always a result of aircraft passing through a shallow, mid-level cloud deck -- in this case, altostratus clouds. When supercooled water droplets in such clouds are jostled by the passage of a jet or airplane, they instantly freeze forming countless ice crystals. The latent heat released by the freezing warms the air and acts to evaporate the portion of the cloud surrounding the entry point of the aircraft. As the ice crystals fall from the hole they have a gauzy or fuzzy appearance -- referred to as a fallstreak.

Of note is the colorful patch of light at center. On this morning, most of the falling crystals happened to have nearly the same orientation, were at the same elevation as the Sun (from the observers' viewpoint) and were about 22 degrees away from the solar disk (out of view at left). The result: when sunlight refracted through the crystals this delightful sundog or parhelion formed. Photo taken on October 10, 2016.

Photo Details: Top - Camera Maker: Apple; Camera Model: iPhone SE; Focal Length: 4.2mm (35mm equivalent: 39mm); Aperture: ƒ/2.2; Exposure Time: 0.0001 s (1/10989); ISO equiv: 25; Software: Adobe Photoshop CS3 Windows. Bottom - same except: Exposure Time: 0.0000 s (1/25641); ISO equiv: 32.