Pressure and wind

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# Pressure and wind - PowerPoint PPT Presentation

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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### 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)
• Force per sq. meter
• kilopascals (kPa) 1kPa=10mb
• Normal sea-level pressure is 1013.2mb, 29.92 inches/Hg, 14.7 psi
Wind
• 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
• Primary forces:
• Gravity (g)
• Coriolis
• Friction
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
• 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
• http://www.classzone.com/books/earth_science/terc/content/visualizations/es1904/es1904page01.cfm?chapter_no=visualization
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

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