Rare cloud formation seen in Antarctica

http://news.yahoo.com/s/ap/20060801/...ctica_clouds_4

HOBART, Australia - Some of the coldest temperatures on Earth brought a
rare cloud formation to the skies over Antarctica, scientists said
Tuesday.
ADVERTISEMENT

Meteorological officer Renae Baker captured spectacular images of the
nacreous clouds, also known as polar stratospheric clouds, last week at
Australia's Mawson station in Antarctica.

The clouds only occur at high polar latitudes in winter, requiring
temperatures less than minus 176 degrees Fahrenheit. A weather balloon
measured temperatures at minus 189 degrees Fahrenheit on the day the
photos were taken.

Resembling airborne mother-of-pearl shells, the clouds are produced
when fading light at sunset passes through water-ice crystals blown
along a strong jet of stratospheric air more than six miles above the
ground.

"Amazingly, the winds at this height were blowing at nearly 230
kilometers (143 miles) per hour," Baker said on the Australian
government's Antarctic Division's Web site.

Australian Antarctic Division atmospheric scientist Andrew Klekociuk
said the clouds are seldom seen, but are occasionally produced by air
passing over polar mountains.

"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.

http://news.yahoo.com/s/ap/20060801/...ctica_clouds_4