Antarctica is the coldest continent
Larger than Europe, with a roughly circular shape, this continent is nearly centred on the South Pole, and is surrounded by the three oceans of the Southern Hemisphere: the Atlantic, Pacific and Indian Ocean.
In the Arctic region, where there is a frozen ocean (the Arctic Ocean) surrounded by continents, the situation is quite the opposite.
Antarctica is colder than the Arctic, precisely because of this different geographical configuration, to which must be added the influence of altitude
: due to the huge ice sheet covering the continent (about 90% of the ice, which corresponds to about 80% of fresh water on the Planet, is found in Antarctica) the average altitude is around 2,000/2,400 metres, with large areas above 3,000 metres, far higher than in the other continents, where it's around 700/800 metres.
These factors cause, at least in the lower layers of the atmosphere, an atmospheric circulation that prevents the penetration of mild ocean winds towards the interior: air and sea currents flow around the continent with an almost circular motion, from west to east (the so-called Antarctic Circumpolar Current
Below the ice, there are plains and even depressions, caused also by the enormous weight of the ice. However, there are mountains as well, culminating in the 4,892 metres high Mount Vinson, not far from the Weddell Sea.
Along with the Ross Sea, the Weddell Sea is a large and partially (but permanently) frozen sea, which enters inside the continent.
The total size of the ice sheet (the one that covers the mainland plus the marine one) vary from about 14 million square kilometres in March, to about 22 million km² in September: in autumn the ice advances by about 4 km a day, and at the end of winter, virtually the entire continent is surrounded by sea ice. The largest iceberg which calved from the stretch of ice, was 40 km wide and 400 km long, so it was larger than Belgium.
The average temperatures of the continent are extremely low. At the South Pole
(2,800 metres above sea level) the average annual temperature is -48 °C: in the warmest month (January) it's about -26 °C, while in the coldest month (August) it's about -59 °C. The lowest recorded temperature is -83 °C, while the highest is -13 °C.
Here are the average temperatures of the South Pole.
Average temperatures - South Pole
Anyway, the lowest temperature on record, which is also the world record, belongs to the Soviet Vostok
station, 3,500 metres above sea level, which in 1983 recorded -89 °C. Here the highest temperature ever recorded is -22 °C. This station is located near the geometric centre of the continent. This shows how continentality, even more than latitude, is a determining factor in the distribution of temperatures, also in Antarctica.
Average temperatures - Vostok 2
There are also inland areas, with no weather stations, where even lower temperatures have been measured by the satellite, such as Dome A, located at 4,000 metres above sea level, where a temperature of -93 °C has been estimated.
The coastal regions
have a much milder climate, due both to lower altitude and lower latitude, but also to the influence of the sea: here even in winter the temperatures rarely drop below -30 °C, while in summer they can exceed the freezing point. The highest temperatures in the continent have been 14.5 °C, recorded on January 5, 1974 at Vanda, a station located near a salt lake in the McMurdo Dry Valleys, at a latitude of 77 °S, and 14.8 °C, recorded in the Argentinian Base Esperanza (see below).
In the Australian Casey Station
, located on the coast of the Indian Ocean, at a latitude of 66 °S, the average temperature goes from -15 °C in May, which is the coldest month, to 0 °C in January.
Average temperatures - Casey
At Esperanza Base
, located in the southern and warmest part of Antarctica, at the tip of the Antarctic Peninsula, at a latitude of 63 ° south, the temperature is even higher, so that the average temperature goes from -11 °C in June, to 0.5 °C in January.
Average temperatures - Esperanza
Above: the annual average temperature in Antarctica (in degrees Celsius).
Along with the record of low temperatures, Antarctica holds also the record of the strongest winds
: winds between 100 and 200 kilometres per hour are not uncommon, but sometimes they even exceed 300 kph, with maximum guts of about 360 kph.
The blizzard is so terrible that it is an obstacle to human activities, even larger than the cold itself. It usually blows from inland to the sea, it's more intense in winter than in summer, and it's due to the huge difference in temperature (and hence in air pressure) that is generated between inland and coastal areas.
The wind causes a huge wind chill
(the phenomenon whereby the wind causes to the human body a perception of more intense cold, compared with real temperatures), so that the perceived temperature in the worst moments can be far lower than -100 °C.
Since the winds blow from the higher elevations of inland areas, and descend in altitude to reach the coast, they are called katabatic
. In the formation of these winds, the general atmospheric circulation plays also a role: at high altitudes the mild subtropical winds arrive, with the "purpose" to prevent the continue cooling of the continent, and then these air masses, having cooled down above the ice cap, descend downslope and towards the boundaries of the continent.
In the station of Dumont d'Urville, for example, there are on average 11.6 days per month in which the wind exceeds 100 kph, with a minimum in January (7 days), and a maximum in August and September (14 days).
This station have experienced at least one episode with wind gusts stronger than 230 kph in all the months of the year, and the overall record, which occurred in June, is an astonishing 324 kph
These icy winds, once they reach the sea, feed the low pressure systems that give life to the West Wind Drift; these winds sweep the ocean north of Antarctica, causing a stream of water which travels from west to east at a speed of 20 Km per day.
Winds shape the surface of the ice and snow in a manner similar to the sand dunes of the desert. Even precipitation in Antarctica is almost everywhere similar to that of the desert, because on average it's lower than 50 millimetres per year, and only near the coast it exceeds 300 mm, with peaks of 600 mm. Strange as it may seem, fires are dangerous, due to the limited availability of liquid water.
Above: the average annual rainfall in Antarctica (in millimetres). The coldest areas are also the driest.
Looking at the two maps, we can see that there is a correspondence between temperature and precipitation. An average temperature of -25 °C roughly corresponds to an average precipitation of 400 mm, while temperatures below -55 °C correspond to values of precipitation below 50 mm. This is explained by the fact that at -55 °C, the saturated vapor pressure is 30 times lower than at -25 °C: in other words, the air can hold much less moisture and then cause less precipitation.
Here is average precipitation in the Casey station, which being on the coast is relatively rainy, or rather snowy. However, given the temperature, it is possible that in summer some rain may fall.
Temperature inversion and optical phenomena
amount in the continent is not very abundant: the months of the long polar night are followed by the spring and summer months, when the sun is often shielded by clouds. Snow and ice cap reflect most of the solar radiation that reaches the ground, while in winter the absence of sunlight determines a radiation deficit, which tends to cool the soil. This determines a unique temperature inversion
, which in winter can exceed 30 degrees Celsius between the ground and 1,000 metres above, also due to the warmer subtropical currents which flow, as mentioned, at high altitude. In July 1989, at Vostok a difference of 34 °C were recorded between the ground, where the temperature was -78 °C and 600 metres above, where it was -44 °C: still at 8,000 metres the temperature was -73 °C, so it was higher than at the ground.
Along with electromagnetic factors, temperature inversion is responsible for curious optical phenomena
, such as sundogs and halos around the sun or moon.
Due to low temperatures and strong winds, in Antarctica the air has an exceptional transparency, brilliance and sound: it is possible to see mountains even at a distance of 550 km.
The absence of objects such as trees and houses, however, makes it very difficult to evaluate the distances. Effects such as light refraction and reflection cause also frequent mirages
, favored by the presence of tiny ice crystals that are formed continuously in the air due to low temperatures.
Meteorological observations in Antarctica began very late, partly because of adverse environmental conditions. Prior to 1957-58, the International Geophysical Year, the only stations were in the Antarctic Peninsula and the Ross Sea. But scientists soon became aware of the importance of knowing the climate of the continent, as well as of the privileged point of view for the study of past and present climate of the Earth (ice layers preserve the memory of the chemical composition of the atmosphere of past ages, from which we can deduce the air temperature), but also for the climate prediction of the future. Phenomena such as global warming and the ozone hole, which was discovered here and here has its greatest intensity, have attracted and still attract groups of scientists who continually defy the cold and the wind to carry out their studies.
Changes and trends
In Antarctica the temperature variations from year to year are considerable: the standard deviation of the mean annual temperature is generally from 0.61 to 1.56 °C, while for example in London it's 0.5 °C.
The differences in the average temperature from one year to another can also be about 4 °C.
As for the trend, the South Pole does not show a clear tendency of increasing temperature, while coastal areas show a remarkable rise of almost 0.3 °C on average every 10 years in the last 40 years (with peaks of 0.5 °C), i.e. more than three times the world average.
On the contrary, until a few years ago there seemed not to be an increasing trend in temperature in the Arctic.
Contrary to what happens in the rest of the world, where the glaciers are retreating both is the mountains and in the Arctic (Greenland and the North Pole), the extent of the ice in Antarctica has actually increased (though less than how much it has diminished in the rest of the world). Contrary to what one might think, even this phenomenon may be due to global warming: on the one hand because in cold regions the increase in temperature allows an increase in snowfall (as long as the temperature remains below freezing), on the other because the greater extent of ice might be due to the greater speed at which the ice from the inner part of the continent slide towards the periphery, and then towards the sea.