December 20, 2007
The Pretty (But Deadly) Clouds
(note: article excerpt and all images are from NASA/Ames Research Center)
The clouds are glimpsed perhaps once a year on those rare winter days when stratospheric temperatures are exceptionally cold.
These clouds were thought to be little more than a colorful curiosity until the 1980s when the Antarctic ozone hole was discovered and satellites showed that polar stratospheric clouds (PSCs) formed much more frequently than observers on the ground had previously thought.
Researchers at NASA Ames were the first to suggest that PSCs were composed of nitric acid particles instead of water ice crystals.