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Antarctic Winds & the Wind Chill Factor

Aurora AustralisAntarctica is well known for its ferocious winds and blinding storms. Its reputation as the windiest and least hospitable continent on earth is well-deserved. Localized blizzards and life-threatening wind-chill temperatures are an ever-present danger. Travel and outdoor activities become virtually impossible during the Antarctic winter season. Along the coast, cold dense air flowing down off the ice-cap funnels through topographic channels at great speeds lifting snow high off the ground and reducing visibility to only a few feet. In the interior, inversion winds coupled with the extremely low temperatures have led to many a tragic end to an Antarctic expedition.


Wind Chill Factor

  • The wind chill factor is a measure of the cooling effect of wind.
  • Wind increases the rate at which a body loses heat, so the air on a windy day feels cooler against exposed skin than the temperature indicated by a thermometer.
  • This heat loss can be calculated for various combinations of wind speed and air temperature and then converted to a wind chill equivalent temperature (or wind chill factor).
  • What is Wind?

    Wind is the movement of air from areas of higher pressure to areas of lower pressure. These pressure differences are caused by differences in temperatures. Generally, colder temperatures develop higher pressure due to the sinking of cold, dense air towards the Earth's surface. Lower pressure is due to warm air rising from the surface of the Earth. The rotation of the Earth causes these winds to curve as they move from an area of higher pressure to an area of lower pressure.

    In Antarctica, the wind patterns observed are part of a larger, global pattern of atmospheric circulation. Due to the round outline of the Antarctic continent, the circulation is relatively uniform with few irregularities to complicate weather patterns.Thus, the continent is ringed by a series of weather "bands", each of which has its own particular weather conditions.


    Types of Winds

    The Wild Westerlies
    A broad band of strong westerly winds occurs between 30°S and 65°S. The latitudes in this region have been referred to as the Roaring Forties, Furious Fifties, and Screaming Sixties!


    Antarctic Circumpolar Trough Winds
    Between 60°S and 65°S latitudes lies the Antarctic Circumpolar Trough, a zone of low pressure that contains variable winds flowing from west to east. In this region, fierce storms sweep warm moist air from the middle latitudes toward the pole, causing clouds and precipitation. Storms usually last for a few days, before a brief clearing, then another storm system.

    The Coastal (Polar) Easterlies
    Between the Antarctic Circumpolar Trough and the continent, a narrow ring of easterly winds exists. Cold winds flowing off the continent are diverted to the west as a result of the Coriolis effect. Conditions here are often calmer and clearer than in the Antarctic Circumpolar Trough.

    On the Polar Plateau
    The center of the East Antarctic Ice Sheet is called the Polar Plateau because its average height is almost a mile above sea level. Its surface is relatively smooth with a slight slope. On average, a zone of high pressure exists here throughout the year resulting in lighter winds and clearer days, although oceanic storms do occasionally penetrate inland to create hazardous conditions.

    Did you know?
  • The Drake Passage is the stretch of water between the most southerly tip of South America and the most northerly tip of the Antarctic peninsula.
  • It has been described as the roughest stretch of water in the world.
  • It is the place where not only are there gale force winds that blow most of the time, but also where the "Circumpolar Current" is squeezed through its narrowest gap.
  • The rate of flow averages around 140 million tons (cubic meters) of water per second, the equivalent of 5000 Amazon rivers.
  • Inversion Winds
    Some of the fiercest and most deadly Antarctic winds are created by temperature inversions on the high interior ice plateau. The Polar Plateau offers a constant source of extremely cold air which settles close to the ground due to the force of gravity. This pool of dense air flows from the high continental interior down toward the coast, just like a river. The Coriolis effect deflects these inversion winds toward the west, creating the coastal easterlies.

    Katabatic Winds
    Most of the interior surface winds move over a gentle slope. However, indentations and channels in the landscape can force the airflow to converge, like placing a finger partway over a flowing water hose. This strengthening and intensifying effect on air flow creates what are called katabatic winds (katabasis is Greek for descent). Katabatic winds begin as inversion winds. Like inversion winds, they are gravity-driven but they flow down the much steeper slopes of the coastal regions. The winds are surface winds, only reaching heights of about 1500 feet, although this height varies. Wind speeds can accelerate suddenly from quiet conditions to 60 feet per second (40 mph).

    The most famous site for Katabatic Winds, and the windiest spot on Earth, is Cape Dennison at Commonwealth Bay. Convergent katabatic flow from the East Antarctic Ice Sheet results in a mean annual wind speed of 50 miles per hour (80 kilometers per hour)!

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    LAND OF EXTREMES


    "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).
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    Gales reach 200 mph on Commonwealth Bay, George V coast.
    Driest: Average precipitation is less than 2 inches per year.
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