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Frequently Asked Questions
about Antarctic Weather
Antarctica is synonymous with cold, thanks to its polar location, its high elevation, its lack of a protective, water-vapor filled atmosphere, and its permanent ice cover which reflects about 80% of the sun's radiation back into space. The South Pole is located within a permanent polar high created by the normal Hadley Circulation. This creates an extremely cold air mass which descends at the poles of the Earth. Unlike the Arctic region, Antarctica is a continent surrounded by an ocean which means that interior areas do not benefit from the moderating influence of water. During the winter, the size of Antarctica doubles as the surrounding sea water freezes blocking heat from the warmer surrounding ocean water.
The Aurora Australis or Southern Lights are mesmerizing, dynamic displays of light that appear in the Antarctic night skies. They appear in many forms -- pillars, streaks, wisps, haloes, and curtains of vibrating color. Auroras are caused by collisions between electrically charged particles from the sun and gases in Earth's upper atmosphere. These collisions produce electrical discharges which energize atoms of oxygen and nitrogen causing the release of various colors of light.
Katabatic winds occur where cold, heavy air flows down the slopes of the inland mountains and the ice plateau. This is a frequent phenomenon as the continent is dome-shaped and the interior is very cold. As a surface flow, these winds may be smooth and low in velocity, but there are many times when they become exceedingly turbulent, sweeping up any loose snow in their path. This fierce, turbulent air may suddenly just appear and produce localized Antarctic blizzards, where the skies are still clear and no snow actually falls to the ground.
"Mock sun" (also "sun dogs") is a colloquial term for a phenomenon called "parhelion" which occurs fairly commonly in polar atmospheres. It is a false image of the sun, created by the bending of rays of sunlight within crystals of ice in the atmosphere. Parhelia are usually observed in pairs, one on each side of the sun and at the same elevation. They tend to be red-coloured on the side nearest the sun. Parhelia are quite close to the sun when the sun is close to the horizon, but move further away as the angle above the horizon increases.
Cold air holds less moisture than temperate air. This is because the molecules of air are packed so tightly that it's as if the moisture has been squeezed out of it. This means that the air in Antarctica is very dry. Relative humidities in the interior average less one tenth of one percent! Most visitors to Antarctica pack a few extra bottles of moisturizer before setting foot on the continent!
The South Pole is located within a permanent polar high, making it possibly the most consistently cloudless place on Earth where there is a scientific station. Although there is lots of snow and ice around, the Pole is really a desert environment, because it averages less than 1 inch of precipitation yearly, about the same as the Sahara Desert. When warm moist air does make it all the way to the Polar Plateau, the air cools and becomes supersaturated with ice crystals. Ice crystals account for 90% of the accumulation on the plateau.
A common feature of the polar plateau is a temperature inversion. A temperature inversion occurs when the coldest temperatures occur at the Earth's surface, and warmer temperatures are some distance above the surface (normally, temperature decreases with height). The temperature inversion may be only 330 feet (100 meters) thick, but the temperature difference can be 54°F (30°C) in that 330 feet! The intensity of inversions is related to altitude and latitude, and is greater in the winter. Strong winds, cloud cover, or precipitation can destroy inversions. Inversions are an important generator of wind across the continental interior.
This is the region of the Southern Ocean encircling Antarctica, roughly around latitude 55 degrees South but deviating from this in places, where the cold waters of the Antarctic Circumpolar Current meet and mingle with warmer waters to the north. This mingling creates local variations in weather, such as fogs, and also a concentration of marine plants and animals because of its higher than average nutrients.
Many people think of Antarctica as a windy place. That is true, but only near the edges of the continent. High on the plateau, at the South Pole, the average wind speed is typically less than 10 miles per hour, with the peak winds rarely over 25 miles per hour. Cold, dense air tends to settle at the Pole making for relatively calm and clear, yet frigid conditions.
Blizzards are a typical Antarctic phenomenon in which very little, if any, snow actually falls. Instead the snow is picked up and blown along the surface by the wind, resulting in blinding conditions in which objects less than a meter away may be invisible.
Whiteouts are another peculiar Antarctica condition, in which there are no shadows or contrasts between objects. A uniformly grey or white sky over a snow-covered surface can yield these whiteouts, which cause a loss of depth perception -- for both humans and wildlife.
"Antarctica is the coldest, highest, windiest, driest, and iciest continent on earth"
Coldest: -129° F at Vostok, July 21, 1983 (World low temperature record.)
Highest: Average elevation 8200 feet (2500 meters).
Windiest: Gales reach 200 mph on Commonwealth Bay, George V coast.
Driest: Average precipitation is less than 2 inches per year.
Iciest: The thickest ice found is in Wilkes Land, where it reaches a depth of 15,669 feet (4,776 meters ).
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