New study explains the coldest temperatures in Antarctica

According to a new study published this week in the journal AGU, tiny valleys near the top of the Antarctic Ice Sheet reach temperatures near -100 degrees Celsius Letters of geophysical research. The discovery could change scientists' understanding of how low temperatures can reach the Earth's surface, and how that happens, according to the researchers.

After reviewing data from several Earth observation satellites, scientists announced in 2013 that they had found surface temperatures of -93 degrees Celsius (-135 degrees Fahrenheit) in several locations on the Antarctic Plateau of the East. South Pole. This preliminary study has been revised with new data showing that the coldest sites actually reach -98 degrees Celsius (-144 degrees Fahrenheit). Temperatures are observed during the southern polar night, mainly in July and August.

When the researchers announced for the first time that they had found the coldest temperatures on Earth five years ago, they determined that clear, persistent skies and light winds are needed for temperatures to go down. as low. But the new study adds a twist to the story: not only is clear skies needed, but the air must also be extremely dry, as water vapor blocks heat loss from the surface snow.

The researchers observed ultra-low temperatures in small depressions or shallow troughs in the Antarctic ice sheet where cold, dense, and descending air forms above the surface and may remain for several days. This allows the surface and air above to cool even further, until the clear, calm, dry conditions degrade and the air mixes with the air. warmer air higher up in the atmosphere.

"In this area, we see periods of incredibly dry air, which allows the heat of the snow surface to radiate more easily in the space," says Ted Scambos, senior scientist at the National Center. Snow and ice data from the University of Colorado Boulder and the main author of the study.

The record of -98 degrees Celsius is about as cold as possible on the surface of the Earth, according to the researchers. In order for the temperature to fall so low, clear skies and dry air must persist for several days. Temperatures could drop a bit more if conditions lasted several weeks, but this is extremely unlikely, Scambos said.

Find the coldest place

The high altitude of the Eastern Antarctic Plateau and its proximity to the South Pole give it the coldest climate of all regions of the planet. The lowest air temperature ever measured by a weather station, -89 degrees Celsius (-128 degrees Fahrenheit), was recorded at the Russian Vostok station in July 1983.

But weather stations can not measure temperatures everywhere. Thus, in 2013, Scambos and his colleagues decided to analyze data from several Earth observation satellites to see if they could find temperatures on the plateau even lower than those recorded at Vostok.

In the new study, they analyzed satellite data collected during the winter of the southern hemisphere between 2004 and 2016. They used data from the MODIS instrument aboard the Terra and Aqua satellites. NASA as well as NOAA polar operational environmental satellite data.

The researchers observed that snow surface temperatures regularly dropped below -90 degrees Celsius (-130 degrees Fahrenheit) almost every winter in a vast plateau region, at more than 3,500 meters above sea level. . Within this vast region, they discovered that dozens of sites had much colder temperatures. Nearly 100 locations achieved surface temperatures of -98 degrees Celsius.

The atmosphere in this region can sometimes have less than 0.2 mm of total precipitable water above the surface. But even when it is dry and cold, the air traps some of the heat and returns it to the surface. This means that cooling rates are very slow as surface temperatures approach the recorded values. Conditions do not persist long enough – it can take weeks – for temperatures to plummet below record levels. However, the temperature measured by the satellites is the temperature of the surface of the snow, and not the air above. Thus, the study also estimated air temperatures using nearby automatic weather stations and satellite data.

Interestingly, even though the coldest sites extended over hundreds of kilometers, the lowest temperatures were almost the same. This led them to wonder: Is there a limit to the cold on the set?

It's really cold?

Using the difference between the satellite measurements of the lowest surface temperatures at Vostok and three automated stations, and the air temperatures at the same place and at the same time, the researchers deduced that the temperatures of the air are the coldest. probably around -94 degrees Celsius, or about -137 degrees Fahrenheit.

The research team has also developed a set of instruments designed to survive and operate in the coldest places of the winter and measure the temperatures of the snow and the air . They plan to deploy the instruments in the next year or two, during the Antarctic summer when temperatures are relatively mild of -30 degrees Celsius (-22 degrees Fahrenheit).

Explore further:
NASA finds weakening of tropical cyclone Fakir

More information:
T. A. Scambos et al, Ultra-low surface temperatures in East Antarctica from thermal infrared satellite mapping: the coldest places on Earth, Letters of geophysical research (2018). DOI: 10.1029 / 2018GL078133