Coldest spot on Earth identified by satellite

High Plateau Antarctica's dry and clear conditions allow heat to be radiated very efficiently out into space

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The coldest place on Earth has been measured by satellite to be a bitter minus 93.2 Celsius (-135.8F).

As one might expect, it is in the heart of Antarctica, and was recorded on 10 August, 2010.

Researchers say it is a preliminary figure, and, as they refine data from various space-borne thermal sensors, it is quite likely they will determine an even colder figure by a degree or so.

The current record low of minus 89.2C was also measured in Antarctica.

This occurred at the nearby Russian Vostok base on 21 July, 1983.

It should be stated this was an air temperature taken a couple of metres above the surface, and, as such, receives the recognition of the World Meteorological Organization as the official coldest place on the planet.

The new satellite figure, on the other hand, is the "skin" temperature of the ice surface itself - what you would feel if you put your hand on it. But the corresponding air temperature would almost certainly have beaten the Vostok mark.

"These very low temperatures are hard to imagine, I know," said Ted Scambos from the US National Snow and Ice Data Center in Boulder, Colorado.

"The way I like to put it is that it's almost as cold below freezing as boiling water is above freezing. The new low is a good 50 degrees colder than temperatures in Alaska or Siberia, and about 30 degrees colder than the summit of Greenland.

"It makes the cold snap being experienced in some places in North America right now seem very tame by comparison," he told BBC News.

Dr Scambos was speaking here in San Francisco at the American Geophysical Union (AGU) Fall Meeting, the largest annual gathering of Earth scientists.

The 2010 cold spot was just south of a ridge running between Dome A and Dome F

He and colleagues have been examining the data records from polar orbiting satellites stretching back some 30 years.

They find the coldest moments in Antarctica occur in the dark winter months at high elevations, where the extremely dry and clear air allows heat to be radiated very efficiently out into space.

It is evident that many super-cold spots are "strung out like pearls" along the ridges that link the high points, or domes, in the interior of the continent.

They are not quite at the ridge crests, but set slightly back down the slope.

"Air chilled near the surface flows downhill because it's denser; and it flows into these very shallow topographic pockets," explained Dr Scambos.

"If you were standing in one of these places, you'd hardly notice you were in a topographic low - it's that gentle and that shallow. But it's enough to trap this air.

"And once in those pockets, the air can cool still further and get down this extra three or four degrees below the previous record air temperature in Vostok."

The cold pockets run in a line for hundreds of kilometres between Dome Argus (Dome A) and Dome Fuji (Dome F). They all achieve more or less the same low temperature between minus 92C and minus 94C. The minus 93.2C figure is the temperature event in which the team has most confidence. It was recorded at a latitude of 81.8 degrees South and a longitude of 59.3 degrees East, at an elevation of about 3,900m.

Hottest place

One of the spacecraft instruments being used in the study is the Thermal Infrared Sensor on the recently launched Landsat-8.

It has very high resolution, but because it is so new the team says more time is needed to fully calibrate and understand its data.

"I'd caution Guinness not to take this result and put it in their world record book just yet, because I think the numbers will probably adjust over the coming year," Dr Scambos told BBC News. "However, I'm now confident we know where the coldest places on Earth are, and why they are there."

The intention at some point is to get some meteorological equipment into the cold pockets to measure the corresponding air temperature just above the surface. When that happens, Dr Scambos believes, Vostok will lose its official coldest title.

By way of comparison, the hottest recorded skin temperature on Earth - again by satellite sensor - is the Dasht-e Lut salt desert in southeast Iran, where it reached 70.7C in 2005.

The coldest place in the Solar System will likely be in some dark crater on a planetary body with no appreciable atmosphere. On Earth's Moon, temperatures of minus 238C have been detected.

BBC Weather presenter Peter Gibbs explains how he found life living in Antarctica for two years

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

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