1. II. Global Energy Balance

2. A. Electromagnetic Radiation: self-propagating electric and magnetic waves. Or …. Radiation transmitted through the vacuum of space without a medium. Moves at the speed of light. 1. wavelength: distance between two successive peaks or troughs.

3. II. Global Energy Balance A. Electromagnetic Radiation: self-propagating electric and magnetic waves. Or …. Radiation transmitted through the vacuum of space without a medium. Moves at the speed of light. 1. wavelength: distance between two successive peaks or troughs. 2. Although we describe electromagnetic (EM) radiation as a wave, it also sometimes behaves like a stream of particles; one particle = photon. 3. Rules of thumb: Shorter wavelength EM has higher temperature/energy Longer wavelength EM has less energy/lower temp.

4. II. Global Energy Balance A. Electromagnetic Radiation B. Electromagnetic Spectrum 1. Radiation comes in a vast range of wavelengths

6. II. Global Energy Balance A. Electromagnetic Radiation B. Electromagnetic Spectrum 1. Radiation comes in a vast range of wavelengths. 2. The electromagnetic wavelength determines its properties. 3. Hot bodies radiate at shorter wavelengths than do cooler bodies. 4. About 50% of solar EM radiation is in the visible spectrum, 40% at longer wavelengths (mostly infra-red [IR]), and 10% shorter (ultra-violet [UV]).

7. Sun Earth (288 K) UVIRVisible 5800 K

8. II. Global Energy Balance A. Electromagnetic Radiation B. Electromagnetic Spectrum 1. Radiation comes in a vast range of wavelengths. 2. The electromagnetic wavelength determines its properties. 3. Hot bodies radiate at shorter wavelengths than do cooler bodies. 4. About 50% of solar EM radiation is in the visible spectrum, 40% at longer wavelengths (mostly infra-red [IR]), and 10% shorter (ultra-violet [UV]). Infrared is longer, so less energetic than visible light; Ultra-violet is shorter wavelength, so more energetic. This is one reason UV light is so damaging.

9. II. Global Energy Balance A. Electromagnetic Radiation B. Electromagnetic Spectrum new terms: flux, blackbody Flux: the amount of energy or material that passes through a given area over a specific time period.

10. II. Global Energy Balance A. Electromagnetic Radiation B. Electromagnetic Spectrum new terms: flux, blackbody Blackbody is an object that emits/absorbs electromagnetic radiation with 100% efficiency at all wavelength. Earth and Sun approximate blackbodies.

11. Sun is about 5500 °C (5800 K), and has a peak EM radiation at about the middle of visible spectrum, whereas Earth is cooler (15 °C) and emits peak energy in the IR range (sensible heat). ** Because Earth’s EM wavelength is about 20 times that of the Sun, we call Earth’s radiation “long wave” and Sun’s radiation “short wave”.

12. II. Global Energy Balance A. Electromagnetic Radiation B. Electromagnetic Spectrum C. Planetary Energy Balance: this is based primarily on: 1. flux of solar radiation (predicted by temperature of the Sun, and Earth’s distance from the Sun). 2. proportion of solar radiation reflected (planetary albedo). 3. from these, we calculate Earth’s average planetary temperature to be –18 °C. The actual average temperature is +15 °C (60 °F). 4. The Greenhouse Effect.

13. II. Global Energy Balance D. Structure and composition of the atmosphere 1. Composition

14. II. Global Energy Balance D. Structure and composition of the atmosphere 1. Composition 2. State of the atmosphere: a. Temperature (C, K, F) b. atmospheric pressure 1 atm = 760 mm Hg = 29.92 inches

15. II. Global Energy Balance D. Structure and composition of the atmosphere 1. Composition 2. State of the atmosphere: a. Temperature (C, K, F) b. atmospheric pressure c. humidity relative humidity: fraction of water vapor in a parcel of air compared to its maximum capacity absolute humidty: the actual volume of water vapor in a given mass of air.

16. Stratosphere Troposphere Mesosphere Thermosphere Inherently unstable Inherently stable

18. Tropopause

19. II. Global Energy Balance D. Structure and composition of the atmosphere 1. Composition 2. State of the atmosphere: a. Temperature (C, K, F) b. atmospheric pressure c. humidity 3. Vertical structure a. inversions b. adiabatic lapse rate Rule of thumb in the Troposphere: Temperature decreases 6 °C for every 1000 m elevation gain.

20. II. Global Energy Balance E. Heating the Atmosphere 1.The fate of solar radiation Reflection (albedo), absorbtion, scatter, selective scatter 2. Heat transport mechanisms a) Conduction b) Radiation c) Convection

21. Radiation Conduction Convection Radiation

22. II. Global Energy Balance E. Heating the Atmosphere 2. Heat transport mechanisms a) Conduction b) Radiation c) Convection d) Latent heat vs Sensible heat Sensible Heat is measured directly by temperature (the speed at which the molecules are moving) Latent Heat is the heat energy gained or released in the transition from one phase to another (gas - liquid - solid)

24. Radiation Conduction Convection Radiation Latent Heat (water vapor)

25. II. Global Energy Balance F. Greenhouse Effect 1. Unlike solids (blackbodies), gases are not blackbodies. Many gases are selective absorbers and emitters. 2. Greenhouse Gases (GHG): gases that are transparent to short wave solar radiation, but opaque a some wavelengths of Earth’s longerwave radiation. 3. Important GHG

27. II. Global Energy Balance F. Greenhouse Effect 4. How do GHG absorb EM radiation? Molecules (like CO 2, H 2 O v ) rotate and vibrate. EM radiation of specific wavelengths are absorbed and increase either the rotational speed or the vibration amplitude of these molecules.

28. II. Global Energy Balance F. Greenhouse Effect Molecular rotation

30. 5. Why do some GHG have a greater “Greenhouse Potential” than others? Because there are “windows” in Earth’s greenhouse, EM wavelengths where there is little or no absorbance. GHG that absorn in these windows are more effective, molecule for molecule, than more H 2 O or CO 2