1. The Earth’s Atmosphere

2. The Atmosphere Present Atm. N 2 (78%) O 2 (21%) Ar (1%) CO 2 (0.04%) H 2 O (varies) …others Early Atm. N 2 CO 2 H 2 O H 2 S HCN …others Where’s the H and He?

3. The origin of the atmosphere Atmosphere formed early ( > 4 Ga) –Formed by outgassing of the early Earth Volcanic gasses (H 2 O, CO 2, SO 4 ) H and He lost to space Around 3.8 Ga cooled enough to allow liquid water (rain, oceans) CO 2 dissolved in liquid water and was consumed by early weathering N 2 (and Ar) doesn’t react with water or rx and was concentrated in the atmosphere O 2 didn’t appear until ~ 3.5 Ga due to ---? Present day O 2 conc. wasn’t achieved until 400 mya.

4. An addendum Comets may have played a role –In deliver in much of the H 2 O to the early earth –Possibly in delivering organic molecules Including amino acids which survive impact… … and can even polymerize to form peptides This has raised the question: were the building block for life delivered from space?

5. The evolution of the atmosphere The increase of O in the atmosphere allowed the formation of ozone - O 3 O 2 + photon -> 2 O 2O + 2O 2 -> 2O 3 Ozone absorbs UV radiation and protects the surface from UV light which destroys cells

6. The Modern Atmosphere

7. Atmospheric Pressure Figure 3.3 Hydrostatic Equilibrium

8. Profile of atmospheric temperature Figure 3.2 What cools the atmosphere? What heats the atmosphere?

9. Temperature Inversion Height Temperature Lapse Rate: 6.4°C/km Daytime Nighttime

10. What creates the lapse rate? Heating at the bottom: Increases temperature Decreases density Less dense hot water rises… Displacing the cooler, denser water at the top Denser, cool water descends… Where it is heated

11. Convection in the atmosphere Ideal gas law and Conservation of Energy

12. HIGH LOW

13. Stable and Unstable Atmospheric Conditions Figure 7.18  Temperature/  Altitude = Run/Rise =1/slope 0°/km-6°/km-10°/km -6.4°/km INVERSION

14. Cold Air Drainage

15. Temperature Inversion, Revisited

16. Large Scale Atmospheric Circulation If Earth Didn’t Spin

17. Large Scale Atmospheric Circulation Coriolis effect

18. Why does it rain in equatororial rain forests? First, we have to know something about water Absolute Humidity –The amount of water in the air (g water/volume air) Relative Humidity –The amount of water in the air relative to the total amount of water that the air can hold –Usually expressed as a % the maximum amount

19. Absolute vs. Relative Humidity Temperature Decreases Relative Humidity Increases

20. Coastal Deserts Coastal deserts

21. Dew Point When you reach saturation (RH = 100%) because of changing the temperature (not the absolute humidity), you’ve reached the dew point Below the dewpoint, air is “super-saturated” and the moisture will begin to condense out

22. Condensation in the Atmosphere and Latent Heat

23. Convective Clouds Energy from the Sun Heats the surface and causes evaporation (evapotranspiration) Evaporation takes a lot of heat: Latent Heat of Vaporization (540 cal/g) Warm, Moist Air Rises, Expands, Cools Hits the dewpoint, starts to condense on CCN As water condenses, (latent) heat is added back to the air as sensible heat The cool dry air is no longer buoyant It starts to subside The air mass is now drier and warmer (at a specific altitude)

24. Why does it rain in equatororial rain forests? Why is it dry in midlatitude deserts?