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Thursday, October 4, 2012

COLD OUT OF THE NORTH




There are THREE reasons that the temperatures are lower in the areas near the Earth's poles.
  1. The amount of energy that reaches the polar regions is less, because the sun's heat strikes at a shallow angle (it is seen along the horizon, not overhead); most is reflected away and more is absorbed by the atmosphere before it can effectively heat the surface.
  2. The reduction in solar heat allows the accumulation of snow and ice, which are more reflective of sunlight than darker surfaces.
  3. The inclined angle of the Earth to its orbit means that we have seasons : the sun appears to travel a different path in summer than in winter. But for points north of the Arctic Circle, or south of the Antarctic Circle, the Earth's tilt means that the Sun is UP for six summer months (never appears to set) and DOWN for six winter months (never rises). The apparent motion is circling, barely above or barely below the horizon. During the winter, even the small heat from the Sun is not received, the only source of heat being ocean currents and winds. This drops temperatures and permanently freezes much of the precipitation into ice.
At the North Pole, the lack of land area means the cold climate creates a winter ice pack on the surface of the Arctic Ocean, and this never fully melts again. At the South Pole (and in Greenland), centuries of accumulation have created immense ice caps, and glaciers. These features reinforce the colder temperatures year-round.

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