Heat Transfer & Winds

1. Heat Transfer & Winds

2. Convection Currents in the Troposphere: • Heat from the Sun is the driving force behind these convection currents • The Sun heats the Earth – air on surface to warms up • Warm air rises • As the air rises, it cools - density to increase and it will eventually sink back towards the Earth’s surface.

3. Why are convection currents in the atmosphere so important? • As warm air rises it begins to cool which allows the water vapor in the air to condense into clouds • Without clouds there would be no precipitation

4. What causes wind? • All winds are caused by differences in air pressure • These differences in air pressure are often caused by unequal heating of the atmosphere • Remember: • Air warms = expands • Cold air = contracts • Important note: • Do not worry about the exact temperature of the air. • Cooler air = high pressure • Warmer air = low pressure.

5. Atmospheric Pressure: • ‘Weight of the atmosphere’ • Measured using a barometer • Can be expressed in either inches of mercury or millibars (mb)

6. Pressure Gradient Force: • Air will always move from an area of high pressure to an area of low pressure

7. Cyclones: • Center of low pressure where air converges • In the northern hemisphere cyclones spin counterclockwise L

8. Anticyclones: • Center of high pressure where air diverges • In the northern hemisphere anticyclones spin clockwise H

9. Weather Associated with a Cyclone: • The air is converging at a center of low pressure which will cause the air to rise • As the air rises it will cool and may condense into clouds • When a cyclone (low pressure) = potential for precipitation and foul weather

10. Weather Associated with an Anticyclone: • The air is diverging at a center of a high pressure which will cause the air to sink • Sinking air = stabilizes the atmosphere in that area = prevents the formation of clouds • When an anticyclone (high pressure) = brings clear skies and no precipitation

11. Local Winds: • Are named after where they come from • Do not effect a very large area • Santa Ana Winds in Southern California- • Hot, dry air comes down from the mountains • Temperature of the are can reach 100°F • Contributes to wildfires in the area

12. Local Winds: sea breeze • During the day - land heats up more quickly than the water • High pressure over the water • Low pressure over the land • Since air moves from high pressure to low pressure, the wind will blow from the water to the land L H

13. Local Winds: land breeze • After the sun sets - land will lose heat faster than the water • This results in high pressure over the land and low pressure over the water • Since air moves from high pressure to low pressure the wind will blow from the land to the water H L

14. Global Wind Belts: calm areas • Doldrums- • Around the equator = area of low pressure • Even though the air rises very quickly there is very little horizontal movement and therefore very little wind.

15. Global Wind Belts: trade winds • High pressure -> low pressure near the equator. • Winds generally blow from the northeast in the northern hemisphere and the southeast in the southern hemisphere • These are some of the most consistent and predictable winds on Earth

16. Global Wind Belts: (continued) • Prevailing Westerlies- • Comes from the west -> east • Polar Easterlies- • Comes from the east -> west • Polar Front- • Where the polar easterlies and the westerlies meet up • In this location the mixing of warm and cold air has a major effect on weather changes in the US

17. Jet Streams: • Bands of high speed winds about 10km above the Earth’s surface • The bands are very wide • Blow from west to east at speeds of 200-400 km/hr • As they travel around the Earth they wander along a wavy path