RARE ANTARCTIC SUMMER CLOUDS

[Anonymous]

Extreme Conditions Create Rare Antarctic Clouds
SYDNEY
(Aug. 08) – Rare, mother-of-pearl colored clouds caused by extreme
weather conditions above Antarctica are a possible indication of global
warming, Australian scientists said on Tuesday.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.Australian Antarctic Division scientist
Andrew Klekociuk said such clouds are occasionally produced by air
rising over Arctic and Antarctic mountains in high polar latitudes
during winter.”You have to be in the right part of the world in winter,
and have the sun just below your horizon to see them,” he said.Nacreous
clouds can only form in temperatures lower than minus 112
Fahrenheit.Meteorologist Renae Baker said a weather balloon in the
vicinity of the clouds in the stratosphere about 12 miles above the
Earth’s surface measured temperatures as low as minus 124.6 F.”That’s
about as cold as the lowest temperatures ever recorded on the surface
of the Earth,” Baker, who photographed the clouds, said in a
statement.Klekociuk said the 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,” he said.Klekociuk
said temperatures in the stratosphere, between 5 and 31 miles above
Earth, would be expected to drop as global warming increases. Data
collected over the past 25 years had reflected this, he told Australian
Broadcasting Corp. radio.”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,” he said.The delicate
cloud colors are created at sunset when fading light passes through
tiny water-ice crystals blown along on strong jets of stratospheric
air.She said winds at the same height were measured blowing at almost
143 mph.

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August 3, 2006 at 12:05 PM