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

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

This occurred at the 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 the satellite figure is the “skin” temperature of the ice surface itself. But the corresponding air temperature would almost certainly beat 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.

AntarcticThe 2010 cold spot (red) 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.”

By way of comparison, the hottest recorded spot 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

 

Rainfall decline in Australia.


Ice cores reveal Australian  rainfall decline Researchers from the ACE CRC and the Australian Antarctic Division have found evidence from ice cores of a long term decline in average annual rainfall in eastern Australia, with records revealing that rainfall since about 1920 is below the average of the past 1000 years.

Australia’s instrumental climate records extend back only about 100 years and show an apparent decline in eastern Australian rainfall. However rainfall in eastern Australia is highly variable, and the significance of the decline can only be assessed when compared with a much longer record.

ACE CRC glaciologist Dr Tessa Vance and colleagues from the Australian Antarctic Division (AAD) and UTAS have obtained the 1000-year record from ice core data. The research, published in Journal of Climate, shows a direct correlation between the instrumental eastern Australian rainfall record and sea salts deposited by winds at Law Dome in East Antarctica over the past 100 years. The 1000-year-old Law Dome sea salt proxy provides the longest rainfall record yet for eastern Australia.

“The El Niño-Southern Oscillation, or ENSO, climate mode predominantly drives rainfall in eastern Australia and is one of the factors that affects winds in the Southern Ocean,” Dr Vance said.

Unlike many other continents, such as North America and Europe, Australia generally lacks suitable climate proxies (such as tree rings) for rainfall prior to the instrumental record. “We weren’t expecting such a strong correlation between two areas this far apart. Normally proxy records come from the region that you are trying to describe,” Dr Vance said.

The proxy record shows that the dry period since the 1920s is similar to a dry period from 1000-1260 AD. Scientists attribute both dry periods to either stronger or more frequent El Nino events. In El Niño-like years, summertime winds in the Southern Ocean are reduced, leading to lower than average concentrations of salts in the ice core. In La Niña-like years, the opposite occurs, with higher summertime winds causing higher concentrations of salts.

Dr Tas van Ommen leads the AAD Climate Processes and Change Program and is a co-author on the study. “This work builds on a 2010 study from the AAD which identified other mechanisms linking Antarctica with the drought in Western Australia, and it shows how important Antarctic climate studies are to understanding climate processes in Australia and the Southern Hemisphere,” he said.

Future research will work towards understanding whether the current dry period had similar climate drivers to the period from 1000-1260 AD. The record will also be extended back another 1000 years, increasing understanding of the Australian climate for the past 2000 years.

Source: Science Alert