Antarctica Lecture 1: Climate

Dr. Emslie lent me a wonderful book about Antarctica. It’s an older Reader’s Digest full of information about the continent – the flora and fauna, the extreme climate, and the fascinating history of human exploration of the “last place on Earth.”

I have learned so much from reading this book, and I would like to share some of that on here! There are a ton of interesting facts but I will try to keep it concise. In this first segment, I will discuss Antarctica in its rawest form – its  extreme climate – which impacts every other factor on the continent….

As I am sure many of you are aware, Antarctica is vastly different from the Arctic. While the North Pole is essentially a vast (mostly frozen) ocean surrounded by land, the South Pole is a giant land mass (with many high peaks) 1.5x the size of the United States, covered in a permanent icecap. This contributes to the many differences between the polar ends of the planet. Excellent comparison between the two: http://www.adventure-life.com/articles/pole-comparison-180

While a study between the two poles is fascinating, obviously I would like to return to a focus on my pole! (The South Pole is the cooler pole, after all!) And in this post, I will discuss the uniquely extreme climate of Antarctica.

Antarctica is, on average, the coldest, driest, highest, and windiest continent. It is actually classified as a desert – only very small amounts of snow and ice crystals fall on the interior each year. The mean annual accumulation is equivalent to less than 50 mm (2 in) of water – this is only slightly more than is received in the Sahara Desert! Much more falls on the coast, particularly on the west of the Antarctic peninsula and parts of east Antarctica. The vast amounts of snow and ice on the continent have been deposited and built up over many millions of years.

Antarctica is separated from the other continents by the Southern Ocean – which in itself plays an important role in global weather patterns. It is famous for being the roughest waters in the world – a region of strong westerly winds and the breeding ground of the great depressions (low pressure centers). They approach (bringing with them warmer and more humid air from over the ocean), and usually dissipate, near the coast of Antarctica where they help to cause a permanent ring of low pressure around the continent at about 60oS, known as the Antarctic Trough.

Ships approaching Antarctica must pass through the so-called “Roaring Forties” and “Furious Fifties” – where the strongest westerly winds sweep almost unhindered right around the Earth.

Radiation at the poles is also an important factor in the weather patterns. The main reason for the low temperature at the poles is that they receive very little short wave radiation from the sun – and what they do receive varies vastly from season to season. There is a maximum in summer, a minimum in winter, and quite rapid changes in spring and autumn. Because of the elliptical orbit of the earth, Antarctica is closest to the sun in summer, and so actually receives 7% more radiation at the southern summer solstice than the North Pole does at the northern summer solstice! At midsummer it even receives more radiation than the equator does at any time throughout the year! So why then does the temperature remain so low? Essentially this is because the snow cover reflects back into space about 80% of the incoming radiation (compared with 5% over ice-free oceans and 15-35% over ice-free land). For most of the year (except for a brief period during midsummer) most of the continent loses more radiation than it gains from the sun.

There are enormous differences in the temperature patterns between summer and winter. This is mainly because of the periods of continuous sunlight in the summer, and continuous darkness in the winter. However, because of the albedo effect, the temperature does not get dramatically warmer in the summer. The final temperature patterns are closely linked to the height of the land, with the sea-level coast being much warmer than the high interior. In the winter, a huge area of the sea around Antarctica freezes – almost doubling the size of the continent. The sea ice also means that the coast is separated from the open sea for much of the year, and thus becomes more continental in climate.

Temperature and wind are the two elements of the weather that are of most importance in the polar regions – and they must be considered together because different combinations contribute to the regional climates of Antarctica. Over most of the continent, the mean temp. of the coldest month is around -15o to -30oC on the coast, and -40o to -70oC in the interior. In summer the mean temp. of the warmest month is around 0oC on the coast and -15o to -35oC in the interior.  It is windspeed, however, which has the greatest effect on human activity. The winds are evidently unlike those experienced in other parts of the world and are of a special type. Their speed and direction are not primarily controlled by atmospheric pressure, but rather by the shape of the icecap. These winds are known as katabic (down-flowing) winds. They are very strong and usually coming from the southeast.

Absolute humidity (the amount of water vapor per volume of air) is always very low because of the low temperatures, which causes many things in Antarctica to dry and shrink. Imported wooden buildings can therefore become a serious fire risk at an expedition base.

Blizzards are a combination of strong wind and falling or blowing snow. They bring all outside work to a halt and can cause considerable damage to unprotected buildings and machines.

A whiteout is a weather condition in which visibility and contrast are severely reduced by snow and diffuse lighting from overcast clouds. There are no shadows, no perceivable landmarks or differences in distance, and a traveler can experience a loss of perception. Even birds have difficulty seeing a snow surface while flying during a whiteout. Aircraft pilots have crashed as a result of disorientation.

Windchill relates wind and temperature to how heat is lost in various conditions. These can be visualized in a windchill index, which ranges from “pleasant” to “exposed flesh freezes”!

Antarctica is a landscape sculpted from water. The most abundant form of freshwater is ice, with about 99% of the world’s surface freshwater locked up in snow, ice, glaciers, and ice sheets that cover 10% of the world’s surface. About 90% of the world’s ice, and 68% of the world’s freshwater is in Antarctica. The Antarctic ice sheet is the world’s largest body of freshwater in the world, containing some 30 million cubic km!

So, if you are still reading, this concludes my first “lecture” on Antarctica. I am doing this to share some of the fascinating things I am learning, and to reinforce my own education about this extreme environment. I will continue to write about the wildlife, human exploration, and other topics, and I hope you learn something as well!

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