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Chapter 2
Weather Factors
Section 3
Winds
What causes wind?
Wind: The horizontal movement of air from an area of high pressure to an area of lower pressure.
What causes winds?
All winds are caused by differences in air pressure
HIGH LOW
What causes these differences in pressure?
• Unequal heating of the atmosphere• Remember convection currents?• As air becomes less dense, its air
pressure decreases.
Measuring Wind
• Winds are described by their direction and speed
Measuring Wind
To measure wind direction: we use a wind vane
Measuring Wind
To measure wind speed: we use an anemometer
Wind- Chill Factor
Wind Chill Factor: Increased cooling caused by the wind
Local Winds
• Local winds: winds that blow over short distances
Local Winds
• Local winds are caused by unequal heating of Earth’s surface within a small area
Local Winds
• Example: cool breezes blowing in from the water to the beach.
Sea Breeze
• Sea Breeze: The flow of air from an ocean or lake to the land.
• Daytime!
Land Breeze
• Land Breeze: The flow of air from land to a body of water.
• Night time!
Sea and Land Breezes
Monsoons
•Monsoons: Sea and land breezes over a large region that change directions with seasons
Global Winds• Global Winds: Winds that
blow steadily from specific directions over long distances
Temperatures• Temperatures near the equator are
much warmer than the temperatures near the poles.
• Temperature differences between the equator and the poles produce giant convection currents in the atmosphere.
Global Convection Currents
This movement of air between the equator and the poles produces global winds.
Global Convection Currents
• Coriolis Effect: The way Earth’s
rotation makes winds curve.
The Coriolis Effect
In the Northern
HemisphereIn the Southern
Hemisphere
Global winds turn toward
the RIGHT
Global winds turn toward
the LEFT
The 3 major wind belts are the:
1. trade winds 2.prevailing westerlies3. the polar easterlies.
Global Wind Belts
The 2 calm areas are the:
1. Doldrums2. Horse Latitudes
Global Wind Belts
• A calm area where warm air rises
• Regions near the equator with little or no
wind
Doldrums
• A calm area of falling air
• Latitudes 30° north and south of the equator
Horse Latitudes
• Steady easterly winds which blow from the horse latitudes
toward the equator.
Trade Winds
•Winds in the mid latitudes which blow from the west to the east.
• Play an important part in the weather of the United States
Prevailing Westerlies
•Cold air near the poles which sinks and flows back toward lower latitudes.
Polar Easterlies
• Jet Streams: Bands of high-speed winds about 10
kilometers above Earth’s surface
Jet Streams