Condensed Water in the Free Atmosphere in Air Colder than −40C

Abstract

Observations of atmospheric clouds formed by hot springs and geysers were made at Yellowstone Park in the wintertime with free atmospheric temperatures warmer and colder than ?40C. Despite careful observations, no evidence could be found of the formation of supercooled clouds at temperatures colder than ?40C. Replicas made of the particles existing under varying atmospheric conditions showed that clouds formed with the air colder than ?40C consisted mostly of frozen, irregularly shaped particles. Liquid droplets were commonly found at temperatures warmer than ?40C. Optical phenomena were virtually absent in the ice particle logs that formed below ?40C. Very complex and spectacular halos, pillars, arcs and circles occurred alter the supercooled clouds formed at temperatures warmer than ?40C were seeded with dry ice or silver iodide.