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Winds
Chapter 2, Section 3p. 52-60
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!
Land Breeze/ Sea Breeze
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
TemperaturesTemperatures near the
equator are much warmer than the temperatures near the poles.
IntermissionChapter 2, Section 3
p. 57-60
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.
Give students this analogy: Assume a plane takes off from some northern location in the U.S. (pick one from your area) and flies several hours due south (pick another location). When the plane arrives, the destination city has moved east due to the Earth’s rotation. To really reach the destination due south, the plane actually has to fly a curved path to where the city will be when the plane lands. This is what happens with the air “turning to the right.”
The Coriolis Effect
In the Northern Hemisphere
In 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
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
Global Wind Belts
Jet Streams: Bands of high-speed winds about
10 kilometers above Earth’s surface
Jet Streams