It’s not too common to see a rainbow in a colorful sunset sky, but sometimes one will suddenly appear, as this one did on April 4, 2006 here in Tucson.
Polar stratospheric clouds (PSCs) form in the stratosphere at altitudes of 50,000–80,000 ft. They are classified into Types I (clouds with more diffuse and less bright colors) and II (nacreous or mother-of-pearl clouds), according to their formation temperature and particle size. Unfortunately, Polar stratospheric clouds play a key role in the massive ozone depletion over the Arctic and Antarctic. NASA explains that PSCs “form only at very low temperatures. They help destroy ozone in two ways: they provide a surface which converts benign forms of chlorine into reactive, ozone-destroying forms, and they remove nitrogen compounds that moderate the destructive impact of chlorine. In recent years, the atmosphere above the Arctic has been colder than usual, and polar stratospheric clouds have lasted into the spring. As a result, ozone levels have been decreasing.”
Photo: NAT GEO
Animated Rainbow - grows and spreading as the winds moves the storm away