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Temperature and Climate
by C. A. Linder

The Arctic has often been referred to as the "Land of the Midnight Sun." The earth rotates around an axis that is tilted by 23½ from the vertical. On the summer solstice (June 21st), all of the Earth's area north of the Arctic Circle (66½N) is bathed in sunlight for 24 hours. Conversely, on December 22nd, the winter solstice, the opposite is true - the Arctic is completely shaded from the sun's light. So if it's sunny all day long in the summer, why doesn't it get very hot? (The summer mean high temperature in Barrow, Alaska is only 45°F!)

There are a number of reasons why the Arctic remains cold, even in summer. The primary reason is that the sun is low on the horizon all day. Thus, solar energy needs to pass through more atmosphere to get to the ground. In addition, the high reflectivity (albedo) of snow and ice surfaces means that very little of the energy that reaches the ground stays there. Therefore, the heat gained during the long summer days is small and highly dependent on topography and albedo. For instance, wet tundra and bare ground absorb more solar radiation than ice sheets. Similarly, wet snow absorbs more radiation than dry snow.

What about the Arctic winter? The mean winter low temperature from Barrow, Alaska is -20F, which is only about 15 degrees colder than Duluth, Minnesota. If the sun never shines all winter at the pole, why isn't the temperature much colder? The answer is related to the global heat budget. The air around the Earth is continually in motion - warm air from the tropics travels toward the poles and cold air from the poles travels toward the equator until a balance is reached. It is the warm air masses from the south that keep the Arctic (relatively) warm, even in the cold, dark winter months.

Arctic climate is influenced by two different air masses: polar maritime (influenced by the ocean) and continental (influenced by large land areas). The ocean influences the climate in the Arctic just like it does in temperate latitudes. For example, when it is 80°F in Boston it is typically only 70°F on Cape Cod - the air near the Cape is moderated by the colder Atlantic Ocean water. Conversely, in winter the ocean is warmer than the land, and the ocean warms up the atmosphere. Since the Arctic region is dominated by the Arctic Ocean, the polar maritime climate subtype is the primary climatic influence. This air mass brings cold, stormy winters and mild, cloudy summers. The interior of the large countries surrounding the Arctic, such as Siberia and Canada, are affected by a continental polar air mass. Just like Boston, they have harsher winters and hotter summers than the coastal regions.

In addition to being cold, the Arctic is also very dry. In fact, the only part of North America that gets less moisture is the desert southwest! This is due in part to the fact that colder air can hold less moisture than warm air. In essence, in winter it is too cold to snow!

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