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Atmospheric Circulation Wind PAGE 122 Atmospheric Circulation AKA Wind! • With all the talk about pollution, global warming and climate change, why do we care? Let those cities with the nasty air enjoy their nasty air by themselves. . . ▫ This thinking leads into our next topic, does it only affect the city that produces the pollution? Unfortunately, no. Wind will carry that pollution all over the globe making this a global problem. The driving force of wind: Convection Currents • Reminder ▫ Convection current: The movement of matter due to differences in density that are caused by temperature variations • This unequal heating transfers heat around the world and causes atmospheric circulation Global Winds • Earth has Three convection cells in each hemisphere that transfer cold air from the poles to the equator and warm air from the equator to the poles • These cells in turn create the prevailing winds, tornadoes, hurricanes etc. Atmospheric Convection Cells • Polar Cell: air cools in the polar regions and flows towards the equator (till about 60º latitude) where it warms, rises, and returns to the poles • Ferrel Cell: known as the “zone of mixing” because the cold polar air from 60º latitude flows down and the warm equatorial air from 30º latitude mix in this area • Hadley Cell: warm air from the equator rises towards 30º latitude, cools and then flows back to the equator What the cells do. . . • All these cells “do” is transfer the heat • This motion of air, in turn, causes the winds • There are 3 major wind belts that generally blow in the same direction all the time, these are called the Global Wind Belts Trade Winds • Prevailing winds that blow from east to west from 30º latitude to the equator in both hemispheres http://www.weatherwizkids.com/globalcirculation.gif Westerlies • Prevailing winds that blow from west to east between 30º and 60º latitude in both hemispheres Polar Easterlies • Prevailing winds that blow from east to west between 60º and 90º latitude in both hemispheres • http://nsidc.org/arcticmet/images/factors/global_circulation.gif Wind Patterns • http://www.youtube.com/watch?v=IWjeHtdpFj E Coriolis Effect-Why the Winds Curve! • The apparent deflection from a straight-line path observed in wind and ocean currents due to Earth’s rotation. • http://www.youtube.co m/watch?v=rdGtcZSFR Lk The Doldrums and Horse Latitudes • Surface winds that are weak and variable that form where convection cells meet ▫ Doldrums or Intertropical Convergence Zone: forms at the equator ▫ Horse Latitudes: forms at 30º latitude Jet Streams • A narrow band of strong winds that blow in the upper troposphere (right before the stratosphere) • Big factor for determining weather • In the upper parts of North America it causes the Polar Vortex, it is actually present year round in the North Pole, but will migrate south Local Winds • Not part of the global wind belts, they depend on local conditions ▫ Sea breeze – cool wind from water to land ▫ Land breeze – cool wind from land to water ▫ Mountain breeze – cool air descends from mountain peaks ▫ Valley breeze – warm air from valleys move upslope Global Circulation • http://www.youtube.com/watch?v=DHrapzHPC SA One More Random Note: Temperature Inversions • Normally, warm air rises, cools and sinks • Here in Utah the topography of the area traps cold air, preventing circulation ▫ This, in turn, traps pollutants also Homework • Complete the diagram provided by labeling the following: ▫ ▫ ▫ ▫ The 3 convection cells (6 total) The 3 global wind belts (6 total) The Horse Latitudes and Doldrums Color the convection cells to show the hot air (red) and cool air (blue) • Answer questions 2-10 on page 125 of your textbook (answer the questions on the back of your diagram)