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 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