IGX

Pileus cloud above the Sarychev volcano as it erupts, Kuril Islands, Russia. Pileus clouds, also called scarf or cap clouds, are small clouds that form on top of a bigger cloud. In this photo a pileus cloud (centre) has formed above a cloud of volcanic ash from the Sarychev volcano. A large plume of smoke, steam and ash is erupting from the volcano while pyroclastic flow of denser ash descends the volcano sides. The picture was taken by astronauts aboard the International Space Station. Note too the ring of non-cloudy air surrounding the volcano that is thought to have been caused by the eruption.

Noctilucent clouds are crystals of ice hanging around 80 kilometres high in the atmosphere that catch the light of the sun long after it has set on the horizon. Natural nacreous clouds occur at altitudes of 20-25 kilometres. The cloud in this image was formed from the exhaust of a missile launched from a distant firing range.

Flying saucer or Lenticular cloud

Cumulonimbus cloud over western Africa near the Senegal-Mali border. Cumulonimbus clouds rise vertically until they hit a natural barrier, known as the tropopause, and then flatten out. Cumulonimbus clouds usually herald the onset of a severe storm. In this image, which was taken from the International Space Station (ISS), several cumulonimbus towers are seen underneath the main cloud, casting a large shadow on the land below.