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Introduction to Antarctica and the Antarctic,

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1 Introduction to Antarctica and the Antarctic,
Why is it so cold? Jean Pennycook

2 Antarctica or Antarctic?
Antarctica is the 5th largest continent on earth and larger than the US and Mexico combined. The word, “Antarctica”, refers to the continent itself. “Antarctic” refers to the entire southern polar region, including the ocean that surrounds this continent. Antarctica is a continent, the Antarctic is a region.

3 The ice that forms the Antarctic glaciers is accumulated snow fall from hundreds of thousands of years. The continent receives only about 2 inches of snow a year so you can imagine how long it has taken to build up 2 km or more in some places. Most of Antarctica is covered with over 2 km of snow and ice. These large glaciers move toward the coast under their enormous weight and the force of gravity. When a portion floats out over the ocean these extensions are called ice shelves. The Ross Ice Shelf is as large as Texas. Source of diagram unknown.but thank you!

4 Ross Ice Shelf Ice shelves are several hundred feet thick. What you see above the water is only about 10% of the entire thickness of the ice. The ice was formed when snow fell several thousands of years ago, in the center of the continent and was pushed towards the coast under the weight of the glacier and the force of gravity. This is the edge of a glacier that is floating on the water, but is connected to the remainder that is on the land. Picture courtesy of:

5 When pieces of these shelves break off they are called ice bergs.
The ice shelf from the ocean. What you see is only 10% of the height of this mass of ice. 90% is under the water. This is fresh water and was made from snow fall.

6 The amount of ice in Antarctica plays a very influential role in the Earth’s temperature. Ice reflects most of the sunlight back into the atmosphere without absorbing it. This helps keep the Earth cool. 92% of Antarctica looks like this. Ice streams form where glaciers are moving towards the coast under their enormous weight and the force of gravity.

7 Map courtesy of Australian Antarctic Data Centre
This map shows the continent of Antarctica. The glaciers are white and the ice shelves are in gray. Red dots indicate a science research station. Antarctica is completely surrounded by ocean. The Southern Ocean is very cold, and is comprised of the largest current on Earth. It flows around the continent from west to east (in a clockwise motion). There is mixing with the ocean waters north, but it is limited. That is one reason Antarctica stays so cold all the time. Map courtesy of Australian Antarctic Data Centre

8 Here is one definition:
So much for Antarctica but what about the Antarctic? It is best defined by ocean boundaries, although politicians usually define it by latitude for convenience. Here is one definition: Any place whose latitude is greater than 66.5o S. In this case here is a map of the Antarctic, defined by what is called the Antarctic Circle. It would include most of the continent of Antarctica and be defined as all places that receive at least one 24 hours of daylight period and one 24 hours of darkness once a year. This boundary would never change as it is defined by latitude. http//

9 Another definition, and the one used by scientists, would be everything south of the Antarctic Polar Front. The polar front or, Antarctic Convergence, is where the cold Southern Ocean, which encircles Antarctica, meets the warmer northern water. This is what the Antarctic defined in that way would look like. This boundary changes slightly seasonally and over the years. This definition includes a much larger area of the Earth and the boundary can change. It is marked by a drop in temperature both in the water and in the air when you cross it. http//:www.

10 You have two definitions of what “Antarctic” means and what area of the Earth would be included. Are there any other ways to define this region? How would you draw the map? One answer: the Antarctic Treaty defines the Antarctic as that portion of the globe south of 60S. Have your students discuss what they think is the best way to define the Antarctic. All these definitions are valid. There are varied definitions that apply to defining the Artic region as well.

11 Why are the Polar regions colder than the rest of the Earth?

12 Imagine a flat Earth SUN
If the earth were flat like this the amount of sun hitting each part of the earth would be the same

13 Consider the black line the total amount of sunlight energy received by the Earth
The black line indicates the amount of sun hitting the earth

14 Now imagine the earth is tilted.
The amount of sun rays or energy would be less

15 Is the amount of sun energy hitting the Earth more or less?
Would the Earth be colder, warmer or the same?

16 Is the amount of energy more or less?
Would the Earth be colder, warmer or the same? The amount of energy would be less even though the size of the Earth has not changes. This means less energy per sq mile so the Earth would be colder. Hint: Is the black line bigger or smaller?

17 Let’s tilt it some more

18 Now what is happening?

19 Even more

20 You get the idea

21 ? What would the earth be like in this case?
The Earth surface would not get any energy from the sun and would be a very cold place indeed.

22 Each of these sun’s rays are equal in size and therefore amount of energy, but notice at 45o angle the amount of land covered by the ray is larger than when the angle is at 90o. Ask your students which of these places under the sun is the hottest. More energy per unit of area will be the hottest so the area under the 90o ray will be hotter.

23 In this picture the sun’s rays are at a 90o angle at the equator and a 0o angle at the poles. The equator will be receiving lots of sun shine and be very warm while close to the poles will receive very little energy and be much cooler. Translate what you just learned to the energy coming from the sun to our Earth’s surface. Where is the angle of the sun 90o and where is the angle very low or no sun at all? Source of diagram unknown

24 If you would like your students to do some math, have them subtract the angle of the sun shown here from 90 and you will get the latitude of each of these lines which are marked on the left hand side. These lines are very important lines on our globe. They are from top to bottom, the Arctic Circle, the Tropic of Cancer, The Equator, the Tropic of Capricorn and the Antarctic Circle. The Earth is only in this position with respect to the sun two days a year, the equinoxes in March and Sept. On these days everywhere on the earth receives 12 hours of day light and 12 hours of darkness. In this diagram you see the angle of the sun is marked for the various places on the Earth. The Earth is in this position with respect to the sun on the equinoxes. Source of diagram unknown

25 Again some math. Here is the extreme of the Earths sun angles and happens on the solstices (June and Dec). See if your students can figure out a relationship between the angle of the sun and the latitudes in this diagram. The Earth is tilted with respect to the sun and this is how the angles of the sun translate as the Earth rotates around it. These angles change with the season. Notice that the sun is at a 90o angle at latitude 23.5oN. This is the Tropic of Cancer and no place north of this line will ever see the sun at 90o. Source of diagram unknown

26 Position of the Earth on the Equinoxes
Position of the Earth on the Solstices Have your students compare these two diagrams. A good classroom activity which illustrates this yearly cycle is for students to mark the suns shadow somewhere around the school building every third or fourth day at the same place and time each day, for a full school year. North facing walls work well. In addition they should make a special note of the shadow length on the equinoxes (Sept and March) and the winter solstice (Dec) Use a strip of adding machine tape to mark the shadow. The tape can be rolled out each time and taped to the building then rolled up and put away. At the end of the year have the students graph the date (x axis) against the shadow length (y axis). The angles of the sun’s rays rotate from the extremes of these two diagrams. Notice at the North and South Poles the angle of the sun never gets greater that 23.5o above the horizon. The latitudes where the sun’s angle is 0 at mid-winter are called the Arctic and Antarctic Circle, respectively (66.5 N & S). The low angle of the sun in the polar regions is one reason why these places are so cold. Source of diagram unknown

27 As the angle of the sun gets smaller towards the poles the amount of energy received by the earth is not a linear relationship. It is a function of the angle as you see in the chart below SIN 80 = 0.98 or 98% SIN 70 = 0.94 or 94% SIN 60 = 0.87 or 87% SIN 50 = 0.77 or 77% SIN 40 = 0.64 or 64% SIN 30 = 0.50 or 50% SIN 20 = 0.34 or 34% SIN 10 = 0.17 or 17% SIN 0 = 0.00 or 0% Translate: If the angle of the sun is 80o then that region receives 98% of the energy it would if the sun were 90o. Or places on the Earth where the sun is 60o above the horizon receive 87% of the energy that a place where the sun is straight up or 90o receives. Skip this slide if your students are not familiar with trigonometry

28 Insolation is the amount of sun energy hitting the earth at a given place.
The units here are Watts per square meter. Watts is a unit of energy, square meter the area of land. The units are not important only that the amount of energy changes with latitude. Have your students calculate the number of boxes under each of theses curves. That would equal the total amount of energy reaching each of these places in one year. Then have them graph the latitude ( x-axis) against amount of energy (y axis) and they will see the total amount of energy received by the poles is very small compared to the equator and the other latitudes. The total amount of energy hitting each of these latitudes in a year is represented by the number of boxes under the curve. Notice the amount hitting the poles is much smaller than the rest of the earth. This is another reason why the poles are so cold. Source of diagram unknown

29 Day / Night Cycle Graph noon midnight noon Look at this diagram and note that it shows the daytime nighttime cycle for Columbus Ohio. You can see the days are longer in June than in December, however every day gets some sunlight and therefore some warming energy. Have your students make the predictions for the shape of the next few graphs by drawing them in their journal or on a white board. Discuss with the class some ideas before going to the next slide. Before you go the next slide predict how this graph will change if you go north, say to Iceland where the latitude is 64.1o N, very near the Arctic Circle.

30 If the students are struggling with this help them by asking the question. The further north you go will the days be longer in the summer or shorter? Did you guess right? Because Reykjavik is near the Arctic Circle there are periods of almost 24 hours sunlight and periods of almost darkness all night. Now let’s go to a place above the Circle say Thule, Greenland. Before you go to the next slide predict what the graph will look like.

31 Thule is well above the Artic circle so there are many days of 24 hour sunlight and 24 hour darkness. Have your student predict what a city ON the artic circle would look like. Did you predict correctly? Since Thule is above the Arctic Circle there are days of 24 hours sunlight and nights of 24 hours of dark. How would this graph change if we went to a similar latitude in the South? Predict first then go the next slide.

32 This is almost the exact same graph as the Thule one
This is almost the exact same graph as the Thule one. You can print this out, cut it down the line at about June 21 and then turn the pages around. Ask your students why the cut would be made at June 21st?. How did you do? Believe it or not this is almost the exact same graph as the one for Thule only the seasons are reversed because McMurdo is in the Southern Hemisphere. Two more: Predict what this graph looks like at the Equator and at the South Pole.

33 If your students get this correct they have a good understanding of this exercise..

34 This graph represents a one day and one night cycle which is what the South pole experiences each year. Ask your students how this explains why the South Pole is so cold. When the sun is up for 6 months it is still cold, why is that so? At the South Pole the sun goes below the horizon on the spring solstice (March 21/22) and does not reappear until the fall solstice (Sept 21/22) The same happens at the North Pole only reversed. Six months of darkness is another reason the Polar regions are so cold.

35 Are the poles equally cold?
You have seen how the orientation of the earth has made for unequal heating of the Earth’s surface. Because of the angle of the sunlight at the Poles they receive less energy and are therefore much colder than the rest of the Earth. You have also seen that the daytime-nighttime cycle provides long periods of darkness for the polar regions which also promote a colder climate Are the poles equally cold?

36 Compare the average T at the North and South Poles
Average Winter oF Average Summer oF South Pole -76 -18.5 North Pole -15 35 Some students might need to be reminded that when the temperature is in the negative degrees, the larger the number, the colder it is. Based on this data, the South Pole is much colder thatn the North Pole. Notice that the South Pole average summer temperature is colder than the average winter temperature at the North Pole Come up with some ideas why this is so.

37 Areas close to large bodies of water are always more moderate in their climate. This has to do with the ability of water to absorb and retain large amounts of heat. The South Pole is a long way from the ocean and therefore much colder than the North Pole. Did you know the South Pole is not the coldest place in Antarctica. A place called Vostok, a Russian research station, is colder because it is the furthest place from the ocean on the continent of Antarctica. The Arctic is a large body of water surrounded by land, but the Antarctic is a large land mass surrounded by water. This is one reason the Antarctic is colder than the Artic.

38 As you can see the water flows through the arctic area mixing warm with the cold. In the Antarctic area there are no land masses to restrict the circular flow of the water around the continent so there is little mixing with warmer northern waters. These maps show the ocean currents for both polar regions. Compare the patterns of the currents. The cold Antarctic water moves in a circular path around the continent and since there are no land masses to deflect it north there is little mixing with those warmer waters. This is quite different from the Arctic and is another reason the Antarctic is colder than the Arctic

39 It’s called adiabatic cooling (or lapse rate)
It’s called adiabatic cooling (or lapse rate). As one ascends in altitude, the air gets thinner, so there are fewer molecules to be holding heat, and colliding with one another to generate it. Remember this slide? Another reason that the Antarctic is colder than the Arctic, is that the average altitude of Antarctica is almost 2 kilometers. All other things being equal, the Earth’s atmosphere decreases by 6.5oC for every 1000 m of altitude that you ascend ( or about 3.5oF per 1000 ft). Source of diagram unknown.but thank you!

40 The cold air descends and spreads across the surrounding sea…
Cold air descending from the higher altitudes and blowing over the continent towards the coast is another reason why Antarctica is colder than the Arctic. The arrows in this map are called vectors. They show the direction the wind is blowing and the strength of the wind. The longer the vector (arrow) the stronger the wind. As you can see the arrows get longer near the coast line. Here the winds become very strong and since they have blown over the land covered with ice they are very cold. From Parrish & Cassano 2001, J Climatology

41 Sea ice in August In winter, the outward spreading cold winds
help to freeze the ocean surface, and the “ice area” of Antarctica (land plus sea ice) doubles. In spring all this ice reflects sunlight, keeping the ocean colder for longer. The sea ice almost doubles the size of Antarctica in the winter. During this time the Adelie Penguins are living in the pack ice far from the land. Sea ice in August

42 Sea ice in February During the summer, without the coldest
winds and the Incessant sun, the sea ice melts around most of the continent, but only for a month before the ocean starts to freeze again as the sun dips lower and lower. The sea ice extent during the Antarctic summer, when most of it has melted. During this time Adelie penguins spend part of their time on land in their breeding colonies. Sea ice in February

43 To sum things up: Antarctica is a continent almost completely covered with ice and snow and is influential in keeping our planet cool by reflecting the sun’s energy back into space. The Antarctic is a region and has more than one definition. Both Polar regions are colder than the rest of the Earth due to the reduced angle of the sun providing less energy, and long periods of darkness when no sun energy arrives. Antarctica is a colder place than the Arctic because it is a land mass and surrounded by a very cold ocean that does not mix with warmer waters in the north. Antarctica is also colder because it is so high in altitude.

44 Other Powerpoint presentations for you classroom:
Introduction to the Polar regions, Why is Antarctica so cold? Introduction to Adelie Penguins, Adelie Penguins march into the classroom. Penguin Adaptations, This is a harsh continent Adelie Penguin Behavior, Good manners are always in style Penguin Predation and Competition, Life is tough for an Adelie Penguin Adelie Penguins Cope with Global Climate Change Did You Know, How researchers know what they know Penguin Quandaries, Can you answer these mysteries Fun pictures about Adelie Penguin Go to The education page.

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