Rare cloud formation seen in Antarctica

Thin clouds made of mixtures of ice, nitric acid, and sulphuric acid form in the upper atmosphere (stratosphere) over the poles when temperatures drop below -78°C (-109°F). Ozone depletion occurs in such polar stratospheric clouds. This particular cloud formation appeared over Iceland at an altitude of about 22 km on February 4, 2003. Its beautiful colors result from the very small size of the ice crystals it contains. These tiny particles bend and scatter the sun’s rays much like a prism. (Photograph courtesy Mark R. Schoeberl, NASA GSFC)