ELECTROMAGNETIC RADIATION MER: form of energy emitted by sun, earth, atmosphere travels through space as electric and magnetic waves

Electromagnetic spectrum Shortwave < 3 µm Longwave > 3 µm

A blackbody is a perfect absorber of all the radiation it receives and emitter of max radiation possible at a given temp

Peak of solar radiation = 1600 W / m2 (Blackbody) 1400 W / m2 (true) Peak of earth (terrestrial) radiation = 470 W / m2

Terrestrial (longwave): 100% infrared 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

Atmospheric “window” of transmission: 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)

Review Pressure, density, mass decrease exponentially with altitude. Atmosphere is therefore “layered”. Troposphere Temperature decreases with height; weather; 90% mass Altitude of tropopause varies with latitude Stratosphere Temp increases with altitude; ozone; stratified Mesosphere Temp decreases with height; lowest temp at stratopause “shooting stars”, noctilucent clouds Thermosphere Temp increase with altitude Auroras

Review SOLAR RADIATION: TERRESTRIAL RADIATION longwave (IR); shortwave (visible, UV, IR); higher radiation intensity; absorbed by ozone and water vapor; atmospheric window of transmission : 0.3 – 0.8 µ TERRESTRIAL RADIATION longwave (IR); lower radiation intensity; absorbed by “greenhouse gases” (O3, H2O, N2O, CO2,CH4) atmospheric window of transmission : 8 – 11 µ

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? between energy

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

Humans maintain skin temp of 91°F (306 K). 1 Humans maintain skin temp of 91°F (306 K). 1. In which portion of the spectrum do we radiate? Wein’s Law: λmax = 2897 / temperature 2. How much energy do we radiate? Stefan-Boltzman : E = σ (T4) σ = 5.67x10-8 Wm-2 K-4 Lambda max = 9.5 microns (thermal IR) SB: fourth power 306 = 8,767,700,496 E = 497 W/sq.m.