1. Electromagnetic Radiation
GLOBAL ENERGY BUDGET - 1
Electromagnetic Radiation

2. Earth’ Surface Temperature
Amount of incident sunlight
Reflectivity of planet
Greenhouse Effect
Absorb outgoing radiation, reradiate back to surface
Clouds
Feedback loops
Atmospheric water vapor
Extent of snow and ice cover

3. The “Goldilocks Problem”
Venus – 460 C (860 F) - TOO HOT
Earth – 15 C (59 F) - JUST RIGHT
Mars – -55 C (-67 F) - TOO COLD

4. The “Goldilocks Problem”
Temperature depends on
Distance from the Sun
AND
Greenhouse effect of its atmosphere
Without Greenhouse effect
Earth’ surface temperature 0 C (32 F)

5. Global Energy Balance - Overview
How the Greenhouse Effect works
Nature of EMR
Why does the Sun emit visible light?
Why does Earth emit infrared light?
Energy Balance – incoming & outgoing
Calculate magnitude of greenhouse effect
Effect of atmospheric gases & clouds on energy
Why are greenhouse gases “greenhouse gases”?

6. Global Energy Balance - Overview
Understand real climate feedback mechanisms
estimate the climate changes that occur
Current
Future

7. ELECTROMAGNETIC RADIATION
50% of Sun’s energy in the form of visible light

8. EMR Self-propagating electric and magnetic wave Moves at a fixed speed
similar to a wave that moves on the surface of a pond
Moves at a fixed speed
3.00 x 108 m/s

9. ELECTROMAGNETIC WAVE 3 characteristics speed wavelength frequencyor
 = c / 
The longer the wavelength, the lower the frequency
The shorter the wavelength, the higher the frequency

10. PHOTONS EMR behaves as both a wave and a particle
General characteristic of matter
Photon – a single particle or pulse of EMR
Smallest amount of energy able to be transported by an electromagnetic wave of a given frequency
Energy (E) of a photon is proportional to frequency
E = h = hc / 
where h is Plank’s constant and
h = x J-s (joule-seconds)

11. PLANK’S CONSTANT E = h = hc / 
High-frequency (short-wavelength) photons have high energy
Break molecules apart, cause chemical reactions
Low-frequency (long-wavelength) photons have low energy
Cause molecules to rotate or vibrate more

12. ELECTROMAGNETIC SPECTRUM

15. ELECTROMAGNETIC SPECTRUM
Infrared (IR) Radiation
40% of Sun’s energy
m (1 m = 1 x 10-6 m)
Visible Radiation / Visible Light / Visible Spectrum
50% of Sun’s energy
nm (1nm = 1 x 10-9 m)
red longest, violet shortest
Ultraviolet (UV) Radiation
10% of Sun’s energy nm
X-Rays & Gamma Rays – affect upper atmosphere chemistry

16. EMR & CLIMATE Visible & Infrared most important Ultraviolet Why?
Sun?
Earth?
Ultraviolet
Drives atmospheric chemistry
Lethal to most life forms

17. FLUX
Flux (F) – the amount of energy (or number of photons) in an electromagnetic wave that passes  through a unit surface area per unit time

18. Flux & Earth’s Climate

19. The Inverse-Square Law
If we double the distance from the source to the observer, the intensity of the radiation decreases by a factor of (½)2 or ¼

20. The Inverse-Square Law
S = S0 (r0 / r)2
where S = solar flux
r = distance from source
S0 = flux at some reference distance r0

21. Solar Flux The solar flux at Earth’s orbit = 1366 W/m2
1 AU = 149,600,000 km (average distance from Earth to Sun)
Venus and Mars orbit the Sun at average distances of 0.72 and 1.52 AU, respectively. What is the solar flux at each planet?

22. The Inverse-Square Law
Small changes in earth’s orbital shape + inverse-square law + solar flux
CAN CAUSE LARGE CHANGES IN EARTH’S CLIMATE

23. TEMPERATURE SCALES
Temperature – a measure of the internal heat energy of a substance
Determined by the average rate of motion of individual molecules in that substance
The faster the molecules move, the higher the temperature

24. TEMPERATURE SCALES Celsius - °C Fahrenheit - °F Kelvin (absolute) – K
boiling and freezing points of water
Fahrenheit - °F
mixture of snow & salt and human body
Kelvin (absolute) – K
The heat energy of a substance relative to the energy it would have at absolute zero
Absolute zero – molecules at lowest possible energy state

25. TEMPERATURE SCALES

26. TEMPERATURE CONVERSIONS
T (°C) = [T(°F) – 32] / 1.8 T(°F) = [T (°C) x 1.8] + 32.

27. TEMPERATURE CONVERSIONS
Convert the following:
98.6 °F to °C
20 °C to °F
90 °C to °F
100 °F to °C

28. ABSOLUTE TEMPERATURE T(K) = T (°C) + 273.15
0 K (absolute zero) = °C
Convert the following:
98.6 °F to K
20 °C to K
90 °C to K
100 °F to K

29. BLACKBODY RADIATION
Blackbody – something that emits/absorbs EMR with 100% efficiency at all wavelengths

30. BLACKBODY RADIATION Radiation emitted by a blackbody
Characteristic wavelength distribution that depends on the absolute temperature of the body
Plank Function – relates the intensity of the radiation from a blackbody to its wavelength or frequency

31. BLACKBODY RADIATION CURVE

32. Blackbody Simulation
Blackbody Simulation

33. WIEN’S LAW
The flux of radiation emitted by a blackbody reaches its peak value at wavelength λ max, which depends on the body’s absolute temperature
Hotter bodies emit radiation at shorter wavelengths
λ max ≈ , where T is temperature in Kelvin
T λ max is the max radiation flux in μm

34. WIEN’S LAW

35. WIEN’S LAW Sun’s radiation peaks in the visible part of EMR
2898 / 5780 K ≈ 0.5 μm
Earth’s radiation peaks in the infrared range
2898 / 288 K ≈ 10 μm

36. WIEN’S LAW

37. ELECTROMAGNETIC SPECTRUM

38. THE STEFAN-BOLTZMANN LAW
The energy flux emitted by a blackbody is related to the fourth power of the body’s absolute temperature
F = σ T4 ,
where T is the temperature in Kelvin and
σ is a constant equal to 5.67 x 10-8 W/m2/K4
The total energy flux per unit area is proportional to the area under the blackbody radiation curve

39. THE STEFAN-BOLTZMANN LAW

40. THE STEFAN-BOLTZMANN LAW
Example: a hypothetical star with a surface temperature 3x that of the Sun
Fsun = σ T4 = (5.67 x 10-8 W/m2/K4) (5780 K)4
= 6.3 x 107 W/m2
Fstar = σ T4 = (5.67 x 10-8 W/m2/K4) (3x5780 K)4 = 34 x σ (5780 K)4
= 81 Fsun

41. THE NATURE OF EMITTED RADIATION
Wien’s Law – hotter bodies emit radiation at shorter wavelengths
Stefan-Boltzmann Law – energy flux emitted by a blackbody is proportional to the fourth power of the body’s absolute temperature
SO – the color of a star (wavelength) indicates temperature, temperature indicates energy flux