Pileus Cloud Over Itanhaém, Brazil

February 18, 2015

Pileus Cloud MeireRuiz (2)

Photographer: Meire Ruiz
Summary Author: Meire Ruiz; Jim Foster
The photo above shows an iridescent pileus cloud observed over Itanhaém, Brazil, on the afternoon of January 1, 2015. Pileus or cap clouds are accessory-type clouds that form above columns of rapidly moving air (updrafts in thunderstorms). If the air the updraft is pushing through is sufficiently humid, close to saturation, then the added lift resulting from the updraft will often cause the column to reach saturation. Clouds riding on this column have a smooth, rounded appearance. In this case, the cloud droplets were of the proper size (about the diameter of the width of a silk fiber) and the storm near enough the Sun to produce iridescence.
Photo Details: Camera: Canon PowerShot SX40 HS; Focal Length: 18.595mm; Aperture: ƒ/8.0; Exposure Time: 0.0005 s (1/2000); ISO equiv: 160; Software: Picasa.