1. Planetary Energy Budget
Current News and Weather
Finish Chapter 2
Electromagnetic Spectrum  
Insolation (Short-Wave Energy)
Terrestrial Radiation (Long-Wave Energy)
Greenhouse Effect
For Next Class: Read Ch. 3 (pp )

2. The Electromagnetic Spectrum
Figure 2.6

3. Wavelength and Frequency
Figure 2.5

4. Solar vs. Terrestrial Radiation
Solar Radiation (Insolation): Short-wave, high intensity, mostly in the visible portion of the EM spectrum.
Source is the Sun.
Terrestrial Radiation: Long-wave, lower intensity.
Source is the Earth and Atmosphere (or Earth-Atmosphere System)

5. Solar and Terrestrial Energy
Figure 2.7

6. Figure 2.9

7. Insolation
What factors influence the average values of insolation (incoming solar radiation)?

8. Seasonality Two important seasonal changes
Sun’s altitude – angle above horizon or Solar Elevation at Noon (SEN)
Day length

9. Annual March of the Seasons
Winter solstice – December 21 or 22
Subsolar point Tropic of Capricorn
Spring equinox – March 20 or 21
Subsolar point Equator
Summer solstice – June 20 or 21
Subsolar point Tropic of Cancer
Fall equinox – September 22 or 23

10. Annual March of the Seasons
Figure 2.15

12. 11:30 P.M. in the Antarctic
Figure 2.16

13. Insolation at Top of Atmosphere
Figure 2.10

14. Solar Elevation at Noon
Figure 2.18

15. Solar Elevation at Noon (SEN)
SEN is the angle of the noon sun above the horizon
SEN = 90˚ - ArcDistance
ArcDistance = number of degrees of latitude between location of interest and sun’s noontime vertical rays
If the latitude of location of interest and sun are in opposite hemispheres, add to get ArcDistance
If they are in the same hemisphere, subtract from the larger of the two values

16. SEN Example What is the SEN on June 21 for Boone (36 N)
SEN = 90 – ArcDistance
Where are the sun’s noontime vertical rays?
ArcDistance = 36 – 23.5
ArcDistance = 12.5
SEN = 90 – 12.5
SEN = 77.5˚

17. Group Exercise What is the Greenhouse Effect and why is it important?
What are the dominant greenhouse gases?

18. Terrestrial Radiation
Greenhouse Effect
Heating of Earth’s surface and lower atmosphere caused by strong absorption and emission of infrared radiation (IR) by certain atmospheric gases
known as greenhouse gases
Similarity in radiational properties between atmospheric gases and the glass or plastic glazing of a greenhouse is the origin of the term greenhouse effect
© AMS

19. Terrestrial Radiation
Greenhouse Effect
Responsible for considerable warming of Earth’s surface and lower atmosphere
Earth would be too cold without it to support most forms of plant and animal life
© AMS

20. Terrestrial Radiation
Greenhouse Gases
Water Vapor is the principal greenhouse gas
Clear-sky contribution of 60%
Other contributing gases:
carbon dioxide (26%)
ozone (8%)
methane plus nitrous oxide (6%)
© AMS

21. Terrestrial Radiation
Greenhouse Gases
Atmospheric window: range of wavelengths over which little or no radiation is absorbed
Visible atmospheric window extends
from about 0.3 to 0.7 micrometers
Infrared atmospheric window from
about 8 to 13 micrometers
© AMS

22. Terrestrial Radiation
Greenhouse Gases
Water vapor strongly absorbs outgoing IR and emits IR back towards Earth’s surface
Does not instigate warming or cooling trends in climate
Role in climate change is to amplify rather than to trigger temperature trends
Clouds affect climate in two ways:
Warm Earth’s surface by absorbing and emitting IR
Cool Earth’s surface by reflecting solar radiation
© AMS

23. Questions?
Take out a sheet of paper and write down any questions about the material we covered in lecture today.