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Pressure and wind. Ch. 4. Air Pressure. If you take a package of air and squeeze or compress it into a smaller area, that air will become higher in pressure. Air will push against sides of package. Barometers. Aneroid Mercury. Air Pressure. Measured in millibars (mb)

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air pressure
Air Pressure
  • If you take a package of air and squeeze or compress it into a smaller area, that air will become higher in pressure

Air will push against sides of package

  • Aneroid
  • Mercury
air pressure5
Air Pressure
  • Measured in
    • millibars (mb)
      • Force per sq. meter
    • kilopascals (kPa) 1kPa=10mb
  • Normal sea-level pressure is 1013.2mb, 29.92 inches/Hg, 14.7 psi
  • Wind is the general horizontal motion of air from one location to another based on differences in air pressure
  • Air speed is measured by an anemometer
moving the atmosphere
Moving the atmosphere
  • Primary forces:
    • Pressure gradient force (PGF)
    • Gravity (g)
    • Coriolis
    • Friction
gravity g
Gravity (g)
  • Why doesn’t the atmosphere collect into a small layer on the ground?
    • Hydrostatic equilibrium:

DP / Dz = -rg

    • What does this say about how pressure changes vertically?
the coriolis effect
The Coriolis Effect
  • When wind moves from zones of high pressure to zones of low pressure it veers due to earth rotation
    • To the right in the northern hemisphere
    • To the left in the southern hemisphere
remembering the direction of bend in the coriolis effect
Remembering the direction of bend in the coriolis effect

Bends to the right

Greatest at poles

Least at equator

Increases with increasing speed

Bends to the left

  • Slows down wind speed
  • In what part of the atmosphere is this most significant?
balance of forces in upper atmosphere
Balance of forces in upper atmosphere

Pressure Gradient + Coriolis =


balance of forces near surface
Balance of forces near surface
  • Pressure Gradient + Coriolis + Friction=
upper air vs surface
Upper air vs. surface



Pressure gradient