There are over 200 different types to look for, but two of the rarest and most beautiful clouds are Nacreous and Noctilucent. Nacreous and Noctilucent clouds form not in the part of the atmosphere in which we live, but much higher up, in the stratosphere and mesosphere. Both are rare clouds and can only be seen, briefly, at sunrise and sunset when all the other lower clouds are in shadow.
A rare and spectacular nacreous cloud (top) appears high in the stratosphere some 20km above Australia's Mawson station in Antartica, July 25, 2006. Australian scientists have said they were studying what rare iridescent clouds over Antarctica can reveal about global climate change. (Renae Baker)
Rare mother-of-pearl coloured clouds caused by extreme weather conditions are seen above Australia's meteorological base known as Mawson Station in Antarctica. Known as nacreous clouds, the formations can only form in temperatures lower than minus 80 degrees Celcius (minus 112 Fahrenheit). (Renae Baker)
The extremely cold temperatures below minus 85 degrees Celsius (minus 121 degrees Fahrenheit) in the rarefied atmosphere show delicate Mother-of-Pearl shell colors produced when the fading light of the Antarctic sunset passed through tiny water-ice crystals blown along on a strong jet of stratospheric air. (Renae Baker)
We were excited on Monday evening to see a beautiful skyscape of polar stratospheric clouds (PSC). These very high clouds are illuminated by the setting sun for several hours after sunset, producing an astonishing spectacle in the late sunset sky. Type 1 PSCs are also described as "stratospheric haze", and type 2 PSCs are known as "nacreous (mother of pearl) clouds" due to the distinctive pearly appearance. The wavy appearance of the whole sky is indicative of very high stratospheric wave flow in high westerly winds at altitudes of 10-25 kms. These clouds are believed to form on ozone destroying particles in the stratosphere and are therefore related to ozone depletion and the annual ozone hole over Antarctica. The cameras were clicking pretty well that evening. - Ivor Harris
We were excited on Monday evening to see a beautiful skyscape of polar stratospheric clouds (PSC). These very high clouds are illuminated by the setting sun for several hours after sunset, producing an astonishing spectacle in the late sunset sky.
Type 1 PSCs are also described as "stratospheric haze", and type 2 PSCs are known as "nacreous (mother of pearl) clouds" due to the distinctive pearly appearance.
The wavy appearance of the whole sky is indicative of very high stratospheric wave flow in high westerly winds at altitudes of 10-25 kms. These clouds are believed to form on ozone destroying particles in the stratosphere and are therefore related to ozone depletion and the annual ozone hole over Antarctica. The cameras were clicking pretty well that evening. - Ivor Harris