1. Midterm #1 - Wednesday!!! Bring a scantron sheet!!!!! No OH’s this week again (last time – I promise) Midterm Review Tonight Broida Hall1610 starting 6:30!!

2. Energy in the troposphere and at the Earth’s surface: A topic not to make light of Chapter 4

3. Questions we will answer today: What is electromagnetic energy? What happens to solar energy once it enters our atmosphere? Why is the sky blue? Why are sunsets red? What is a “green flash?” How does the Greenhouse Effect work?

4. So, which produces energy with shorter wavelengths? The earth or the sun?

5. So, what happens to solar energy once it enters Earth’s atmosphere? CONSEQUENCES TransmissionTransmission Reflection -> AlbedoReflection -> AlbedoPROCESSES Scattering Scattering Absorption Absorption Refraction Refraction

6. Scattering The redirection of light by gas molecules or aerosols without altering its wavelength Atmosphere is denser nearer the Earth’s surfaceAtmosphere is denser nearer the Earth’s surface Interaction between light & gas molecules increasesInteraction between light & gas molecules increases Scattering increases closer to the Earth’s surfaceScattering increases closer to the Earth’s surface

7. Rayleigh Scattering Rayleigh scattering – When particles are much smaller than the wavelength of the incoming radiation, shorter wavelength radiation is scattered much more often than longer wavelength radiation. Blue light is scattered much more than Red!!

8. Mie Scattering when scattering particles are the same size as the wavelength of light Mie scattering - when scattering particles are the same size as the wavelength of light These particles are aerosols Mie scattering affects all visible wavelengths a little stronger for blue than red

9. So why is the sky blue? The most abundant type of solar energy is in the blue wavelength, so blue light is scattered more than anything else. Shorter wavelengths are also scattered more easily than long wavelengths

10. Why are sunrises & sunsets red? Low Altitude Sun – Solar radiation passes through more atmosphere and undergoes more scattering. Why does this cause us to see red?

11. Earth’s Albedo

12. Refraction As light passes from one medium to another (space to atmosphere), it is forced to change speed.As light passes from one medium to another (space to atmosphere), it is forced to change speed. This causes light at different wavelengths to bend at different angles.This causes light at different wavelengths to bend at different angles. What are some examples of refraction in our atmosphere?What are some examples of refraction in our atmosphere?

13. Absorption Any solar radiation that is not reflected back to space is eventually absorbed. Albedo = 31% (31% of incoming energy goes back out to space) Earth’s absorbance = 100% - 31% = 69% Absorbed solar radiation is converted to: 1. Chemical energy via photosynthesis 2. Heat -> longwave radiation (& other processes)

14. Longwave Radiation We know that anything on earth that absorbs shortwave radiation must re-emit it as longwave radiation because earthly objects are much cooler than the surface of the sun: Intensity = σT 4Remember Intensity = σT 4 When T decreases, Radiant intensity goes down & WAVELENGTH INCREASES.When T decreases, Radiant intensity goes down & WAVELENGTH INCREASES.

15. Shortwave & Longwave Energy

16. Earth’s Energy Balance Everything on Earth constantly emits longwave radiation.Everything on Earth constantly emits longwave radiation. On the whole, Earth emits just as much longwave energy to space as the shortwave energy that it absorbs.On the whole, Earth emits just as much longwave energy to space as the shortwave energy that it absorbs. Radiation net = (SW - SW ) + ( LW - LW )Radiation net = (SW - SW ) + ( LW - LW ) AbsorptionEmission

17. Greenhouse Effect components of the greenhouse effect water vapor: 60% carbon dioxide: 25% ozone: 8% other gases like nitrous oxide, methane, and CFCs make up the remainder

18. sunearth compare the ideal curve for earth above with the actual curve at left

19. Earth’s temperature without the greenhouse effect Earth’s average temperature without the natural, enhanced greenhouse effect (i.e., its “black body radiative equilibrium temperature”) would be ~256 K, or -17°C Earth’s actual average temperature is ~288 K, or 15°C the difference is due to the greenhouse effect!

20. The greenhouse effect on other planets atm. pressure (Earth = 1) Tblackbody (K) Tsurface (K) Mars0.007 Venus90 what does this imply about the atmospheric composition of these planets? 216 227750 240 yes, both atmospheres are mostly CO2

21. Confusion between the greenhouse effect & global warming the greenhouse effect is one of the most well validated theories in earth science global warming is driven by greenhouse effect properties of the gases we are adding to the atmosphere: CO2, N2O, CH4,CFCs think of the natural, background greennhouse effect and the anthropogenic, enhanced greenhouse effect cause by human activities

22. ~45% of incoming radiation reaches the surface Energy Balance in the Troposphere

23. Cloud-albedo and cloud-greenhouse forcing

24. Not all clouds are alike in their radiative effects (greenhouse effect properties versus albedo properties) Credit:http://www.ucar.edu

25. DV, Show the Energy Budget Animation

26. high, thin cirrus clouds have a net warming effect (greenhouse effect > albedo effect) low, thick stratus clouds generally have a net cooling effect (greenhouse effect < albedo effect)

27. aerosols can also have a large impact on albedo and the atmospheric radiation budget

28. focus on the Sahara -why does it have both high reflected light but also high losses of longwave radiation? now look at the Amazon, Central Africa, and Indonesia - what causes high reflected shortwave and low longwave losses?

29. Some fundamental concepts the surface is net positive, while the atmosphere is net negative - the two balance one another out taken as a whole, the earth is in radiative equilibrium over an annual cycle

30. 36° N 36° S “If there were no energy transfer the poles would be 25° Celsius cooler, and the equator 14° Celsius warmer!”