Wind

1
Wind

• Wind is the movement of air from an area of high
  pressure to an area of low pressure.
• It is the roughly horizontal movement of air (as
  opposed to an air current) caused by uneven
  heating of the Earth's surface.
• The two major influences on the atmospheric
  circulation are the differential heating between
  the equator and the poles, and the rotation of
  the planet (Coriolis effect).

2
Wind

• The area near the equator receives the most
  concentrated solar radiation, causing the air
  above it to heat up rapidly. As it heats up, it
  expands, becoming less dense and more buoyant.
• This change in density causes it to rise. Air at
  the very top of the rising mass cools and is
  pushed further away as heated air continues to
  rise from the equator

• Air circulation follows a general pattern known
  as a convection cell. Air flows from the equator
  to the poles and back again along a lower path
  resulting in a more even distribution of heat
  around the world.

3
Wind

• The cooler the air gets, the more dense it gets
  causing it to sink back to earth. As it descends
  it warms again and displaces the cooler air close
  to the surface in higher latitudes. This cooler
  air is forced to flow toward the equator
• The key factor driving convection is density
  warm air is less dense and more buoyant than cold
  air.

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Essentials/wind/sequence/lesson4_activity1.jsp
4
Prevailing Winds

• Two factors complicate this general pattern.
• Earths rotation
• The uneven distribution of land and water over
  the Earths surface
• As a result, the movement of air from the equator
  to the polar regions is broken into three
  different convection cells for each hemisphere.
  These include the Trade Winds, the Westerlies,
  the Polar Easterlies, and the jet streams.

• They are constant and predictable and are known
  as prevailing winds. (fig 4.10 p. 63)
• This description is theoretical. Two factors can
  change how prevailing winds blow..
• 1. Variation in the earths surface
• 2. Earths position relative to the sun.

5
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Essentials/wind/sequence/lesson4_activity1.jsp
6
Coriolis Effect

• The tendency for objects or fluids to be
  deflected to the right of their path of movement
  in the Northern Hemisphere and to the left in the
  Southern Hemisphere. This is caused by the
  rotation of the earth.