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