1. Global Wind Patterns Science 1206

2. Lesson Objectives ► using scientific theory, describe and explain heat transfer and its consequences in both the atmosphere and hydrosphere, relating this science to natural phenomena ► identify the different prevailing winds around the Earth ► recognize that high heat transfer between oceans and the air above creates convection currents within the atmosphere ► explain the importance of convection and the Earth's rotation in causing prevailing winds

3. Prevailing Winds ► This lesson will concentrate on the major winds of the Earth called the prevailing winds. ► This lesson will concentrate on the major winds of the Earth called the prevailing winds. ► The prevailing winds are also know as the trade winds due to their importance to trade by sailing ship back in the time of the great explorers.

4. Prevailing Wind Patterns: ► The winds are one of the most important features when discussing weather. ► Wind - the movement of air in the atmosphere. ► Some winds are local while others are prevailing. ► Local winds – occur in a fairly small region. ► Prevailing winds – affect large areas of the earth.

5. The Coriolis Effect: ► Coriolis Effect - In any rotating system anything that moves long distances appear to change direction. ► In the northern hemisphere, The Coriolis effect causes winds to twist to the right of the direction of flow. ► In the southern hemisphere, The Coriolis effect causes winds to twist to the left of the direction of flow.

6. Coriolis Effect

7. ► The prevailing winds are mainly the result from the transfer of heat energy from the land and oceans to the atmosphere. ► The resulting convection currents and interaction with the Coriolis effect creates major wind currents over the globe.

9. Prevailing Winds Equator 30 o north 60 o north 30 o south 60 o south Northeast Trade Winds Mid-latitude Westerlies.

10. Causes of Prevailing Winds: There are combinations of things that cause prevailing winds. They are: ► Convection currents set up in the atmosphere ► Earth’s west to east rotation

11. Northeast Trade Winds:  Warm air from the equator area forms equilateral convection current.  This warm air rises and expands leaving behind an area of low pressure.  As it moves northward, it gets so cold and dense that it sinks down towards the earth’s surface, causing an area of high pressure.

12. Northeast Trade Winds:  The surface air then moves away from this area of high pressure toward the low pressure area at the equator.  This surface air twists to the right as it moves toward the equator causing the Northeast Trade Winds.

13. Mid-latitude Westerlies  At 30° latitude some of the equatorial convection current is deflected northward toward another low pressure area around 60° latitude.  The mid-latitude convection current results when its warm air meets the cold air.  The air twists to the right as it flows northward, causing the mid-latitude westerlies.

14. Polar Easterlies  Near the north pole the air is cold and dense, so it sinks. This causes a high pressure area at the surface. The surface air moves southward, away form this high-pressure area, at the same time twisting to the right, causing the polar easterlies.

15. Effects of Prevailing Winds:  Distributes large amounts of solar energy to colder parts of the world.  Returns a flow of colder air southward.  Carry moisture, causing snow and rain.

16. Jet Streams Jet StreamsJet StreamsJet Streams ► High altitude, fast moving, winds in the troposphere that generally flows from west to east over the mid- latitudes. ► The jet streams separate cold polar air to its north from warmer air to its south. http://www.stuffintheair.com/images/Separ ationJet.jpg

17. Summary: ► Air pressure gradients, or the difference between regions of high and low air pressure, impel air in the direction of lowest pressure, creating wind. The larger the air pressure gradient, the greater the wind speed. The Coriolis effect also affects wind speed and direction.