Wave Clouds Above Midlothian, Virginia

Provided by: Bonnie Keller
Summary author & editor: Bonnie Keller, Jim Foster 

These iridescent wave clouds appeared before my eyes near Midlothian, Virginia, just after noon on a lovely, mid-winter's day. Wave clouds typically occur when stable air is forced to rise over elevated terrain. The resulting “waves” may persist hundreds of miles from where they initially formed. Mid-level altocumulus and altostratus clouds will often show iridescence if they're positioned apparently close to the Sun. Iridescence or irisation is caused by diffraction of sunlight around minute water droplets of various sizes. It seems that the colors are purer when the droplet sizes are more uniform. Photo taken on January 18, 2007.