1. WINDS

2. What is Wind? A horizontal movement of air
Vertical movements of air are currents or updrafts or downdrafts.

3. What is the role of Wind? Moves excess heat from tropics to poles
Moves water vapor from ocean to land
Moves ocean currents
Creates waves on the ocean or other bodies of water

4. What causes wind? Unequal heating of the Earth
Pressure differences because of temperature differences
Winds blow from high to
low pressure areas.

5. What factors affect wind direction?
Pressure gradient
Coriolis Effect
(to the right in the
northern hemisphere)
Friction (slows surface wind speed and weakens Coriolis effect)

6. Winds in Pressure Systems
High Pressure: Clockwise and outward
Low Pressure: Counter-clockwise and inward

7. Global Wind Belts

8. Global Wind Belts
Caused by the Coriolis Effect and Unequal Heating of the Earth
Cold, heavy air sinks
Warm, expanding air rises
More sun at the equator causes air to rise and move toward the poles
The Coriolis Effect causes global winds to turn in certain directions.
Occur over a large area

9. Three main global wind belts
Trade Winds: occur between 30o N and S of the equator; blow west from the NE in the N. Hemisphere and from the SE in the S. Hemisphere
Prevailing Westerlies: occur between 30o and 60o N and S of the equator; blow east from the SW in the N. Hemisphere and NW in the S. Hemisphere
Polar Easterlies: occur between 60o and 90o N and S of the equator; blow west along the polar front; the mixing of warm air and cold air has an impact on weather in the United States.

10. Areas of No Wind
Doldrums: located along the equator because warm air rises creating a low pressure system
Horse latitudes: at 30o N and S of the equator; weak winds; many deserts occur here because of the dry air

11. Jet Streams
Narrow belts of high speed winds that blow in the upper troposphere and lower stratosphere about 10 km up in the atmosphere (wind speed: km/hr)
Separates warm air from cold air
Two per hemisphere: polar and subtropical
Winds blow from W to E but shift N and S
Have an effect on the movement of weather systems.

12. Local Winds
Sea Breezes: H pressure over the ocean and L pressure over the land cause air to move from the water to the land as warm air rises and cold air from the water comes in to take its place (DAY time)
Land Breezes: H pressure over the land and L pressure over the ocean causes air to move from the land to the water as warm air rises and cold air from the land comes in to take its place (NIGHT time)

13. Local Winds

14. Local Winds
Mountain Breezes and Valley Breezes occur in the same way as sea and land breezes