In Antarctica, as the temperatures decline in the fall, the continent cools rapidly. This results in large pressure differences at the edge of the landmass, and leads to an increase in cyclonic or storm activity. The cyclones carry warmer moister air from the northern latitudes into the continent, though they often do not penetrate very far inland.

Blizzards are a typical Antarctic phenomenon occurring when drift snow is picked up and blown along the surface by the violent winds. Blinding conditions can result in which objects less than a 3 feet away may be invisible. Localized blizzards are caused when the surface wind sweeps up any loose snow, even if the skies above are clear and no snow is falling. A severe blizzard may last for a week at a time with winds blasting at over 100 miles per hour.

Blizzard Facts

Byrd Station has blizzard conditions about 65% of the year Blizzards often cause severe damage to buildings and can bury structures under many feet of drift snow. A blizzard is a storm with winds of at least 35 mph and temperatures below 20°F, with enough falling or moving snow to reduce visibility to less than 1/4 mile. Eight or ten blizzards a year are not uncommon to coastal areas, and they bring any human outdoor activity to a standstill.

Polar cyclonic storms are similar to tropical cyclones.They have the same circular shape and bands of clouds.However, they strengthen faster, travel faster (56 kilometers per hour compared to 28 kilometers per hour; 35 miles per hour compared to 17 miles per hour) and carry sleet and snow. Most Antarctic storms occur in the winter when pressure differences are greater and the winds stronger.

In the Southern Hemisphere, cyclonic storm systems usually start in the middle latitudes and move gradually to the south bringing moisture and heat to the frigid Antarctic continent. Most storms travel from west to east, under the influence of the polar westerlies and the Coriolis Effect.

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.

Inland, on the Polar Plateau the storms tend to dwindle as they lose energy, although strong oceanic storms do occasionally create hazardous conditions. On average a zone of high pressure exists over the central portion of the continent throughout much of the year resulting in lighter winds, clearer days, and extreme cold.

Storms and Sea Ice

Strong winds create rough seas for which Antarctica is notorious. Even minimal winds can slow or stop sea ice formation, by agitating the sea surface. Interestingly, the edge of the pack ice actually can cause a shift in the location of the region of maximum storm frequency. Ice growth actually may be increased to the west of storm centers.

Polar cyclones draw much of their energy from temperature contrasts created by the sun's unequal heating of the Earth. This unequal heating is due to the tilt of the Earth's axis and the global distribution of land and sea. When conditions are right, gravity pulls cold, dense air under warmer, lighter air providing the potential energy necessary to create the kinetic energy of storms.

Energy is added to storms when air rises and water vapor in it begins condensing into clouds and precipitation. As this vapor freezes and turns into ice, it releases heat called "latent heat" which adds to a storm's energy. Also, high speed winds in the upper atmosphere can add still more energy to a storm.

A storm's wind speeds depend on the differences between air pressures around the storm and in its low pressure center. The greater the difference, the stronger the winds. As winds spiral in toward a low-pressure area they make a smaller and tighter circle and like the skater who pulls her arms in, the winds spin faster.

Measuring Snow From Storms

Attempts to find the value of precipitation in Antarctica can be frustrating. Because of winds, snow is blown into and out of the gauge, making readings inaccurate. Gusting wind during a major storm with significant new snow may empty a gauge, and during a snowless day, winds may blow considerable snow into the gauge! Precipitation declines inland because of the increased altitude and distance from the sea. Most snow fall occurs in winter when the westerlies are strongest and the storm systems can reach inland farther and more often. Free-standing precipitation gauges that work well in other locations do not work well in Antarctica.