Unformatted text preview: And The Weather’s Good…part II
And The Weather’s Good…part II
AP Env Sci 20102011 Wind
Wind • ALL wind is caused by horizontal differences in air pressure • What is Air Pressure?
– Pressure exerted by the weight of air above
What is the pressure in here?
What units are used for air pressure? (Force/area) millibar = 100 N/m2
– Pressure is set by Temperature and Density of air • Higher Pressure Difference, More Wind What causes the pressure differences?
What causes the pressure differences? • Uneven Heating of the Earth’s Surfaces
– Sea Breeze
– Land Breeze • Temperature Variation > Pressure Variation > Wind If Pressure Acted Alone…
If Pressure Acted Alone… •
• If Earth did not rotate
If there was no friction
Then, air would always flow directly from High pressure to Low pressure • In Reality, three factors control wind:
– Pressure Differences
– Coriolis Effect
– Friction Earth without Rotation… • http://teachingboxes.org/catalog.jsp?id=TBOXR000000000039 Rotating Earth – What Does it Do?
Rotating Earth – What Does it Do?
• Coriolis Effect: – All free moving objects (wind, planes) are deflected right of their path of motion in Northern Hemisphere, left of path of motion in Southern Hemisphere • Video
• Demo: Earth viewed from North Pole Results of the Coriolis Effect
Results of the Coriolis Effect Friction Friction • Most important for air contacting a surface
• Winds aloft – not affected
• At surface, friction slows winds Some “Local” Winds Some “Local” Winds • Land and Sea Breezes
• Mountain and Valley Breezes •
• – Valley breeze: Sun heats air along slopes more intensely, rises
– At night, mountain breeze
Chinook: warm, dry air descending mountain
– Pulled over mountain by low pressure system
– Air is heated by compression as it flows downward
– Cold air over icecovered highland “falls” downhill under influence of gravity
– Antarctica: up to 66 ft/sec Global Winds to Know
Global Winds to Know Image/Text/Data from the University of Illinois WW2010 Project ...
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- Spring '11
- Coriolis Effect