The Weather in Antarctica is nearly always very cold. That’s obvious when we see its place on the globe – the South and North Poles never get much heat energy from the sun – but Antarctica is much colder than the North Pole. Unlike the Arctic, Antarctica is a high land mass surrounded by a cold Southern Ocean, and higher is always colder.
At the South Pole, winter temperatures are routinely around minus 50°C, and often get below minus 70°C in winter. But some parts of Antarctica are even colder. Russia’s Vostok station, nearly 700 metres higher than the South Pole, has the official world record low surface temperature, minus 89.2°C in 1983. Satellites have recorded an even lower surface temperature near Dome Argus, the 4000-metre high point of the ice sheet, but that has not been verified by ground measurements.
So virtually any Antarctic weather forecast will be cold today, cold tomorrow, cold for the rest of the week or month. But that’s just the beginning of the story, read on and learn all about the Weather in Antarctica.
The driest continent
Weather in Antarctica isn’t only the coldest of all continents, but also the driest. That’s hard to fathom considering there are millions of cubic kilometres of ice on the continent, but that ice is made up of snowfalls over many thousands of years. The truth is that away from the coast the sky is nearly always clear and it hardly ever snows, the result of a huge high-pressure system sitting permanently over the Antarctic interior. At Dome Argus annual average precipitation (in the form of ice crystals) is about 20 millimetres.
So over most of Antarctica, a typical daily weather report will be something like “very cold with clear skies (sunny in the summer, starry in the winter) and a persistent light southerly breeze”. That breeze isn’t always southerly – it actually comes from higher points, beginning somewhere like Dome Argus and descending down the slopes of the ice dome, slowly at first and gathering speed as the slope increases. It’s a wind driven by gravity, which is called a katabatic.
By the time a katabatic wind nears the coast, where the slope of the ice sheet is steepest, it’s no longer a breeze. Unbroken by trees or mountain ranges, and concentrated by a landform variation such as an ice depression or a glacier valley, the wind can reach huge speeds. At Cape Denison in East Antarctica (about due south of Tasmania), monthly average winds can reach over 90 km/h, with peak gusts over 300 km/h, making this one of the windiest places in the world.
Accompanying most katabatics is a blizzard, in which snow picked up by the wind and blown horizontally through the air makes it impossible at ground level to see any but the closest features, and sometimes no further than the length of an arm. Such katabatic blizzards are confined to the surface. A few metres up the air is clear.
Wind chill and water
The Weather in Antarctica tend to be much milder at the coast than inland, with a typical maximum around minus 10°C, but when a katabatic is blowing it doesn’t feel it. The reason for this is wind chill: the faster the katabatic the colder you feel. The wind blows away any insulating air close to your body and your body compensates by encouraging you to add clothes and eat hot food, all of which makes the air seem colder than it is. Wind chill is a big factor in frostbite, which happens when the body reacts to cold by withdrawing blood supply from tissues, starting with extremities like noses, fingers and toes.
Sometimes in coastal parts during high summer (January and February) the temperature can get above freezing point. When that happens falling snow becomes rain, ice overhangs begin to drip and form icicles, and hard ice becomes flowing water, transforming the landscape. In extreme cases water can be seen gushing from coastal ice cliffs. With global warming we can expect such melting events to happen more often and last longer.
Weather in Antarctica; stormy, cloudy and wet
The first thing to say about Weather in Antarctica, and especially in coastal areas, is that it’s changeable. A clear, calm day can suddenly change to falling and blowing snow with low visibility and a high wind chill factor. This stems largely from the circumpolar trough, a belt of low pressure systems surrounding Antarctica, which can interact with katabatic winds to produce howling gales. Offshore storms present a significant hazard to shipping.
It’s not just windier around the coast, but cloudier and more moist. While average precipitation over the whole continent is around 150 mm (water equivalent) a year, near the coast it’s more like 250 mm. In some coastal areas snow can rapidly accumulate, so that buildings can be completely covered in snow in a single season. At one place on the coast of West Antarctica, average precipitation has been measured at over 1000 mm a year.
The unstable Antarctic Peninsula
The Antarctic Peninsula, the finger of land that reaches toward South America, is the mildest part of Antarctica not so much because it’s the continent’s most northerly point but because of the influence of the sea along its long coastline. Relatively warm ocean waters make for unstable sea ice, glacier tongues and ice shelves up and down the peninsula’s west and east coasts.
The east coast of the Antarctic Peninsula is cold, with summer temperatures mostly below freezing and winter getting as cold as minus 25°C, and dry, with precipitation rarely above 150 mm a year. But along the peninsula’s warmer west coast, temperatures average above freezing point through summer, and rarely get below minus 10°C in winter. Precipitation averages about 400 mm a year, much of which falls as rain over summer.
Things are changing more rapidly on the peninsula than elsewhere in Antarctica. The rate of ice loss from glaciers and ice shelves is steadily increasing, with many ice shelves partially lost or vanished altogether over the past 50 years, changing the shape of the coastline along both west and east coasts. At the same time, many ice shelves have lost volume from their underside from coming into contact with warmer ocean water.
The islands scattered around Antarctica are, on the whole, milder in temperature but not so mild when it comes to wind, snow and rain. Like the Antarctic Peninsula, coastal islands don’t get much warmer than 1°C in summer or cooler than minus 10°C in winter, although Peter I and Alexander Islands, among others, get colder because of the fast ice that usually surrounds them.
Southern oceanic islands such as South Georgia, Kerguelen, Macquarie and Campbell Islands are characterised by cool summers and cooler winters (cold but not as cold as Antarctica), with a much smaller temperature variation from summer to winter – only about 3°C above or below freezing point. They frequently experience rain in summer, snow in winter and strong winds all year round.
A few other things besides cold set Antarctic weather apart. Weather phenomena like ice-blink and polar mirages, nacreous clouds, and various forms of solar halos are a big part of what makes Antarctica special.
Ice-blink is a sign to mariners that there is ice ahead. It’s a white light seen above a sea horizon, sometimes reflected from low clouds, indicating ice beyond the horizon.
Mirages happen when a cooler layer of air sits atop a warmer one, causing light refraction so that objects on the horizon seem to be floating above the surface rather than resting on it. They can be seen in several forms in polar regions, including Fata Morgana, a distorting, often rapidly-changing mirage seen in winter, or in spring when sea-ice has recently broken up. The Nova Zemlya effect shows a sunrise before it happens, sometimes with a “green flash” – a result of especially large inversion layers stretching over the horizon for hundreds of kilometres.
Polar stratospheric clouds (also called nacreous or mother-of-pearl clouds because of their unique colouring) form in the stratosphere during winter, around 20,000 metres up, and can be seen most clearly in twilight just after sunset. For all their beauty, they are also a sign of ozone depletion occurring because of the chemical reactions that occur in their presence. Another cloud formed even higher in the atmosphere is a noctilucent cloud. This summer-time phenomenon cannot be seen in daylight, so it’s best observed during a twilight north of the Antarctic Circle, where there is some darkness in summer.
Solar halos, solar pillars, sun dogs: All these are the result of light from the sun interacting with ice crystals in the atmosphere and resulting in a wide variety of white and coloured rings, arcs, pillars and spots in the sky. The circular halo is the most common. Other forms include solar pillars, which appears as vertical columns of light rising from the sun near sunset or sunrise, and sun dogs (or parhelia), where a pair of bright spots appear either side on the sun, often together with a circular halo around the sun. All these phenomena are best seen when the sun is close to the horizon.