Thursday, August 03, 2006
Rare, mother-of-pearl colored clouds caused by extreme weather conditions above Antarctica are a possible indication of global warming.
Known as nacreous clouds, the spectacular formations showing delicate wisps of colors were photographed in the sky over an Australian meteorological base at Mawson Station on July 25. Such clouds are occasionally produced by air rising over Arctic and Antarctic mountains in high polar latitudes during winter. Nacreous clouds can only form in temperatures lower than minus 80 degrees Celsius.
A weather balloon in the vicinity of the clouds in the stratosphere about 20 km above the Earth's surface measured temperatures as low as minus 87 Centigrade. These rarely seen clouds, also known as polar stratospheric clouds, were more than just a curiosity. They reveal extreme conditions in the atmosphere, and promote chemical changes that lead to destruction of vital stratospheric ozone. Temperatures in the stratosphere, between 8 and 50 km above Earth, would be expected to drop as global warming increases. Over that time there has been a small decrease in temperature and that change is actually occurring faster than the warming at the surface of the Earth. This delicate cloud colors are created at sunset when fading light passes through tiny water-ice crystals blown along on strong jets of stratospheric air. at the same height winds were measured blowing at almost 230 km/h.
Photo's from news.yahoo.com