APES – Earth’s Heat Engine

1. APES – Earth’s Heat Engine How heat is transported through Earth’s atmosphere and oceans

2. Lecture Overview • How is heat redistributed around our planet? • What creates distinct patterns of rainforests and deserts?

3. Answer: • The sun! • Well… it’s not quite that simple.

4. Where do winds come from? • What happens when you heat molecules? • Heated fluids and gases become less dense and rise • Cooled fluid/gases become more dense and sink Air moves because at one place less dense air rises, while in another place denser air sinks toward Earth cooling Less dense fluid rises More dense fluid sinks A convection cell is formed in the atmosphere when air is warmed at one location and cooled at another heat

5. Where do winds come from? • Idealized Earth with no rotation, no land • Unequal heating like real Earth • Around equator, the air warmed from below rises • Flows toward poles, where it is cooled and sinks back toward the equator • Go to Moving Heat Animation air cools and sinks air rises Fig. 7.16

6. What factors determine the density of air? • Heating and cooling of air and gains and losses of water vapor in the air are related to: • Unequal distribution solar energy over Earth’s surface • Presence or absence of water • Variation in temperature of earth’s surface materials in response to heating • These act to affect the density of air • Temperature - warmer air, less dense • Water vapor – moist air less dense (water has lower molecular weight than dry air) • Altitude – less dense with increasing altitude • Warm moist air is less dense than cool, dry air

7. What is atmospheric pressure? • Atmospheric pressure is the force of a column of air on an area of earth’s surface • High pressure – density of air is more dense than average • Low pressure – density of air is less dense than average • Winds blow from high to low pressure • Winds named from direction they come from N low pressure Is this a North or South wind? high pressure S

8. How are vegetation patterns related to atmospheric circulation? http://www.esa.int/Our_Activities/Observing_the_Earth/ESA_global_land_cover_map_available_online

9. Comment: Better legend for previous map

10. The water cycle is driven by solar energy too • We often think of the water cycle as a local phenomenon • Important globally • Return to Moving Heat Animation

11. How can disrupting the water cycle, change climate?

12. How can disrupting the water cycle, change climate? • The rainforests (and all forests) ‘make’ their own clouds • Transpiration video • Transpiration in Amazon creates rainfall in: • Peru • Bolivia • Argentina • Uraguay • Paraguay and S. Brazil http://www.guardian.co.uk/environment/2009/apr/01/prince-charles-rainforest-funding

13. Energy in Evaporation and Condensation • Energy is transported through atmosphere with the molecules, especially water! • The transfer of energy from surface to atmosphere disrupted.

14. Summarize so far… • How are the water cycle and atmospheric circulation related? • What impacts does deforestation have to both cycles?

15. Tomorrow • Examine the atmosphere in more detail • Normal function of greenhouse gases • Heat trapping properties of certain gases