1. Solar and Terrestrial Radiation
Chapter 3
Solar and Terrestrial Radiation

2. Electromagnetic Spectrum
Electromagnetic radiation travels in the form of waves, and are classified in three ways:
Wavelength, distance from wave crest(trough) to crest(trough)
Frequency, number of waves passing a point in a given amount of time
Energy – higher frequency=higher energy

3. Get familiar with this!

4. BLACKBODY Radiation Laws
The wavelength of the most intensely emitted radiation by a blackbody is inversely proportional to the absolute temperature: Wein’s Displacement Law
lmax = C/T
C=2897, and T is in Kelvin ( K = 0º C)
Hot object’s maximum emission wavelengths are shorter, cold object’s max emission wavelengths are longer.

5. Earth
Sun
10 μm
(Infrared)
lmax = C/T
0.5 μm
(Green light)

6. BLACKBODY Radiation Laws
Law relating the temperature of a blackbody to the amount of energy emitted: Stefan-Boltzman Law
E~T4
E=total energy flux across all wavelengths emitted by the blackbody.
T=absolute temperature of the object

7. Earth’s Motion in Space and the Seasons
Angle of incoming radiation:
Wherever the sun is at its maximum solar angle (90 degrees) is the spot where solar rays are most concentrated.

8. Earth’s Motion in Space and the Seasons
Distance from source of incoming radiation:
Inverse square law…
Earth closest to the sun on January 3 (perihelion) and farthest from the sun (aphelion) on July 4 – earth receives 6.7% more radiation at perihelion than at aphelion. – thanks to the inverse square law.

9. Earth’s Motion in Space and the Seasons
So…the earth is closest to the sun in OUR winter…then why is it colder here during the winter?
Sun’s direct rays at Equator
Sun’s direct rays at Tropic of Capricorn
The tilt of the Earth’s spin axis – 23 degrees 27 minutes.
Sun’s direct rays at Tropic of Cancer.
Sun’s direct rays at Equator

10. Solar Radiation and the Atmosphere
Solar radiation interacts with gasses and aerosols as it travels through the atmosphere…
Reflection = angle of incident radiation equals angle of reflected radiation, albedo = (reflected radiation)/incident radiation)]
Scattering = Scattering by molecules is wavelength-dependant
Absorption = Absorption is actually an energy conversion process – radiation striking the surface of a particle is converted to heat energy

11. Solar radiation and the earth’s surface
The fraction of solar radiation that does make it to the earth’s surface is either reflected or absorbed (increasing the surface’s temperature)
Common Albedos
Urban area: – daytime highs warmer during sunny days
Cirrus clouds: – keeps nighttime temperatures warmer – daytime cooler
Fresh snow: – daytime temps cooler

12. Infrared Response and the Greenhouse Effect
Remember that “Absorption by atmospheric gasses varies greatly by wavelength – will strongly absorb some wavelengths and others little or not at all”
Greenhouse gasses are very transparent to solar radiation, but absorb infrared radiation (emitted by the earth) very well. – These gasses in turn heat, and emit infrared radiation back toward the surface = Greenhouse effect
Global radiative equilibrium keeps the planet’s temperature in check – emission of heat to space in the form of infrared radiation balances the solar radiation’s heating – this equilibrium can be disturbed…

13. Infrared Response and the Greenhouse Effect
Principle greenhouse gasses:
Water vapor – evaporated water – example=DESERT DAILY TEMPERATURE VARIATION
Carbon dioxide – respiration, burning fossil fuels
Methane – decomposition, cows
Nitrous oxide
Ozone…

14. The Stratospheric Ozone Shield
Ozone (O3) – 3 oxygen atoms – relatively unstable
Near the surface – ozone is a air pollutant, and a major contributor photochemical smog (Chapter 2)
Ozone in the stratosphere shields us from lethal intensities of Ultraviolet (UV) radiation – great absorber at UV wavelengths.

15. The Stratospheric Ozone Shield
Ozone is both created and destroyed by UV light – balanced cycle
Creation – UV strikes O2 atoms, causing them to split, and then the two free O attoms collide with existing )two molecules to form O3 (ozone)
Destruction – ozone absorbs UV radiation, slitting the O3 into an O2 molecule and O atom. The free O atom then collides with an O3 atom, forming two separate O2 atoms.

16. The Stratospheric Ozone Shield
CFCs – chlorofluorocarbons
UV radiation breaks CFCs up, yielding Chlorine (Cl) gas…which reacts with and destroys ozone