Transcript ELECTROMAGNETIC RADIATION

ELECTROMAGNETIC
RADIATION
Electromagnetic spectrum
Shortwave < 3 µm
Longwave > 3 µm
Peak of solar radiation = 1600 W / m2
Peak of earth (terrestrial) radiation =
470 W / m2
Solar (shortwave) :
8% UV, X-ray, Gamma
47% visible
45% infrared
Terrestrial (longwave):
100% infrared
λ = wavelength
Atmospheric absorption
Gases in atmosphere absorb at different
wavelengths.
Wavelengths not absorbed are
TRANSMITTED.
absorption vs. transmission
Atmospheric
absorption/transmittance graph
White gaps
are “atmospheric
windows of
transmission”;
black areas are
absorption bands
Shortwave absorbers:
• Ozone: absorbs UV < 0.3 μ
• H2O vapor : absorbs > 0.8 μ
Atmospheric “window” of transmission:
0.3 – 0.8µ (shortwave)
Longwave absorbers:
• H2O vapor, CO2, ozone, CH4, N2O
Another window:
8 – 11 µ (longwave)
Solar constant
amount of solar radiation received at top of
atmosphere on a plane surface
perpendicular to sun’s rays.
(not diminished by atmosphere)
= 1372 W m-2
1 Watt = 1 J / sec
What is relationship
between wavelength
and temperature?
What is relationship
between energy
and temperature?
Rules of Radiation
1. Wein’s Law
all objects emit energy at wavelengths
inversely proportional to their temperature
Wein’s Law gives wavelength of peak
intensity (λmax)
λmax = 2897 / T (temp in Kelvins)
For earth:
λmax = 2897 / 300K = 9.6 μ (infrared)
For sun:
λmax = 2897 / 6000K = 0.48 μ (visible)
For molten lava? (temp = 1073 K)
λmax = 2897 / 1073 =
2.7 μ (shortwave infrared)
2. Stefan-Boltzmann Law
E = σ (T4) (temp in Kelvins)
σ = Stefan-Boltzmann constant:
5.67x10-8 Wm-2 K-4