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. 80-100)

The Electromagnetic Spectrum Figure 2.6

Wavelength and Frequency Figure 2.5

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)

Solar and Terrestrial Energy Figure 2.7

Figure 2.9

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

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

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

Annual March of the Seasons Figure 2.15

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

Insolation at Top of Atmosphere Figure 2.10

Solar Elevation at Noon Figure 2.18

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

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˚

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

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

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

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

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

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

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