Wind Notes
Why Air Moves
• Wind is created by differences in air pressure
• Bigger difference = faster wind
– Caused by unequal heating of earth
Air
• The air by the equator is warm and rises
– Low pressure
• The air by the poles is cold and dense
– High pressure
• Wind will then travel from poles to equator
– Move from area of high pressure to area of low
Pressure Belts
• Wind travels in small belt patters
• It never travels too far because it will cool as it moves and
sink back down
• Moves at a about 30 degrees at a time or down the earth
Earth’s rotation affects wind direction
• Without the earths rotation the global winds
would flow directly from the poles to the
equator.
• Coriolis Effect
– Influence of Earth’s
rotation on objects
that move over Earth.
The Coriolis Effect
• The wind does not travel perfectly north to
south
• Earth’s rotation causes wind to travel in a
curved path
Coriolis Effect
• Global winds curve as Earth turns beneath them.
• Northern Hemisphere
– Winds curve to the right
• Southern Hemisphere
– Winds curve to the left
• Only noticeable for winds that travel long
distances.
• Causes global winds to travel along 3 routes in
each hemisphere
– Routes are called global wind belts
Types of Wind
• Local wind
– Sea Breeze
– Land Breeze
– Monsoon – Seasonal changes in wind
• Global wind
– Doldrums / Horse Latitudes
– Easterlies / Westerlies
– Jet Stream
• Both caused by uneven heating
Global Winds
• The distance winds travel varies.
• Some winds die out quickly
• Global winds
– Winds that travel long distances in
steady patterns over several weeks
– Caused by uneven heating between
the equator and the north and
south poles
Sunlight is
concentrated near the
equator because it
strikes the surface
directly
Sunlight is more
spread out near the
poles because it strikes
at a lower angle
Global Winds Continued
• Near the equator concentrated sunlight heats the
surface to a high temperature. Warm air rises,
producing low pressure.
• In regions closer to the poles, the sunlight is more
spread out. The air above them is cooler and
dense. Sinking dense air produces high pressure
that sets global winds in motion.
Calm Regions
• Doldrums
– Low-pressure zones near equator
– The rising, moist air produces clouds and heavy
rain.
• Horse Latitudes
– High-pressure zones located 30 degrees north and
south of the equator.
– Clear and dry weather
Wind Belts
• Coriolis effect creates 3 wind belts
in each hemisphere
• Trade Winds
– Blow from east. Move towards equator. Die out as
they near the equator
• Westerlies
– Blow from the west. Move towards the poles. Brings
storms across much of the U.S.
• Easterlies
– Blow from the east. Move towards mid-latitudes.
Storms occur when cold air from easterlies meets the
warm air of the westerlies.
Effects of Wind on Travel
• How would wind effect travel?
– Sailors used to dread traveling
through the doldrums and the
horse latitudes because there
wasn’t enough wind.
– To avoid the calm regions,
sailors sought out global wind
belts
– Sailors rely on trade winds to
get across the ocean
Jet streams flow near the top of the
troposphere
• Jet streams
– Flow in upper troposphere
– Travels west to east
– Often moves at high speeds (greater than 124
mi/hr).
– Form because Earth’s
surface is heated
unevenly.
– Loop north and south
Jet Streams
• Each hemisphere has 2 jet streams
• Subtropical jet stream
– Flow closer to poles in SUMMER
• Polar jet stream
– Has a strong influence of weather
– Can pull cold air down from Canada or pull warm air up.
– Strong storms form along its loops
Patterns of heating and cooling cause local winds
• Local Winds
– Some winds change daily in a regular pattern.
– Blow within small areas
• Land breezes and Sea breezes are similar but
opposite.
Land Breeze / Sea Breeze
Land Breeze
• Wind blows from the land to the ocean
• Happens during the Night
• Land cools down causing it to have a low air
pressure
• Water maintains its temperature causing it to have a
higher air
pressure
• Air will move from high
pressure to low pressure
• It will move from the
land to water