Iridescence in pileus cloud II

Iridescence in Florida pileus clouds. Imaged in July '03 by David LaPuma (site) using a Leica Televid 77 APO spotting scope.   The inset shows the area of the main image atop a towering cumulus cloud.  Pileus or "mushroom cap" clouds are formed above cumulus. During the day warm moist air in cumulus rises and the clouds tower upwards. Sometimes their vertical growth pushes up a layer of moist air above them. The air layer expands as it is forced up into lower pressure surroundings and adiabatically cools. The water vapour in it suddenly condenses forming a misty veil-like layer of droplets above the cumulus - pileus cloud. Any cloud formed suddenly has all its droplets of similar size - ideal for iridescence or a corona.  Image ©2003 David LaPuma