Nacreous Clouds over Beauly, Scotland
December 20, 2012
Photographer: Colin McChristie
Summary Author: Colin McChristie; Jim Foster
The photo above shows a bright display of metallic-looking nacreous clouds as viewed near Beauly, Scotland, at dawn on December 9, 2012. Similar clouds were observed at dusk the night before in Aberdeenshire. Nacreous clouds are a type of wave cloud composed of very small (approximately 0.0004 in or 0.01 mm in diameter), similar-sized ice crystals or ice particles. These crystals are responsible for the cloud's iridescent colors. They form in the lower stratosphere, generally on the lee side of mountain ranges or elevated terrain, at extremely low temperatures of -121 F (-85 C) or colder. During this display, winds were howling at about 40 mph (64 km/h). Strong winds aloft and at the surface often accompany the formation of wave clouds, whether they develop in the troposphere or stratosphere.
Photo details: Camera Maker: Samsung Techwin; Camera Model: VLUU L100, M100 / Samsung L100, M100; Focal Length: 18.1mm (35mm equivalent: 111mm); Aperture: f/5.2; Exposure Time: 0.011 s (1/90); ISO equiv: 120; Exposure Bias: none; Metering Mode: Matrix; Exposure: Landscape Mode; White Balance: Auto; Flash Fired: No (enforced); Orientation: Normal; Color Space: sRGB.