This speculator photo of Polar Stratospheric Clouds (PSC’s) were captured over NASA’s Radome at McMurdo Station in Antarctica in September 2013.
PSC’s form at an altitude of between 15,000 and 25,000 metres (49,000-82,000 ft) where temperatures of around -85ºC are reached. The clouds are comprised of ice particles around 10 µm across and it is these ice crystals which set the stage for the characteristic bright iridescent colours. The crystals diffract and interfere sunlight when it is low on the horizon; between 1 and 6 degrees.
While these clouds are undoubtedly beautiful, they are also implicated in the formation of ozone holes. Some PSC’s are more exotic in their ingredients and may contain nitric or sulphuric acid. As a result, their surfaces can then act as catalysts which convert chlorine into active free radicals. During the return of spring sunlight these radicals destroy many ozone molecules in a series of chain reactions.
-Jean
Image courtesy of Deven Stross
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