Earth Systems Science Chapter 3 ELECTROMAGNETIC RADIATION: WAVES I. Global Energy Balance and the Greenhouse Effect: The Physics of the Radiation Balance of the Earth 1. Electromagnetic Radiation: waves, photons 2. Electromagnetic Spectrum 3. Flux 4. Blackbody Radiation 5. Planetary Energy Balance c = speed of light in a vacuum = 3.0 x 10 8 m/s λ = wavelength (m) v = frequency (1/s or s -1 ) ELECTROMAGNETIC RADIATION: WAVES Relationship between v, c, and λ vλ = c λ= c/v Vλ/c = 1 ELECTROMAGNETIC RADIATION: PHOTONS E = hv = hc/λ E = Energy (joules, or j) h = Planck s constant = 6.63 x 10-34 j-s v = frequency (1/s or s -1 ) c = speed of light in a vacuum (m/s) λ = wavelength (m) 1
ELECTROMAGNETIC SPECTRUM http://www.lbl.gov/microworlds/alstool/emspec/emspec2.html FLUX FLUX: INVERSE SQUARE LAW 2
BLACKBODY RADIATION BLACKBODY RADIATION Planck function Wien s Law Stefan-Boltzman law T = temperature (K) σ = Stefan Boltzman constant BLACKBODY EMISSION RATES: PLANCK FUNCTIONS FOR SUN,EARTH At the Sun s surface SOLAR (SHORTWAVE) RADIATION Note: area of circle is used here: Πr 2 SWin = area * flux SWin = Πr 2 S - Πr 2 SA SWin = Πr 2 S(1-A) 3
SOLAR (SHORTWAVE) RADIATION: Why we use the area of a circle SOLAR (SHORTWAVE) RADIATION: Why we use the area of a circle Earth Earth SOLAR (SHORTWAVE) RADIATION TERRESTRIAL (LONGWAVE) RADIATION Net SW = Incoming Outgoing Net SW = Πr 2 S Πr 2 SA Net SW = Πr 2 S (1-A) SWin Energy SWout Note: area of sphere is used here: 4Πr 2 Earth LWout = area * flux LWout = 4Πr 2 σt 4 e 4
TERRESTRIAL (LONGWAVE) RADIATION Net LW = Incoming Outgoing Net LW = 0 4Πr 2 σt 4 e TERRESTRIAL (LONGWAVE) RADIATION Net LW = -4Πr 2 σt 4 e T e = effective radiating temperature Net LW = -4Πr 2 σt e 4 Energy LWout Energy LWout TOTAL RADIATION Assume dynamic equilibrium: IN = OUT Net SW + Net LW = 0 Net SW = Πr 2 S(1-A) Net LW = -4Πr 2 σtt 4 e Πr 2 S(1-A) 4Πr 2 σt e4 = 0 σt e4 = (S/4) (1-A) SWin T e = [ (S/4σ) (1-A) ] 0.25 Energy SWout LWout TOTAL RADIATION T e = [ (S/4σ) (1-A) ] 0.25 S = 1370 W/m 2 A = 0.3 σ = 5.67 x 10-8 W/(m 2 -K 4 ) T e = 255K = -18 C = 0 F 5
GREENHOUSE EFFECT T e = 255K Ts = 288K Tg = Ts-Te Tg = 33K = 33 C = 59 F GREENHOUSE EFFECT SW LW You can do the same calculation including an atmosphere Atmosphere Surface Atmospheric Energy Balance II. Atmospheric Composition and Structure 6
Vertical Pressure and Temperature Structure Vertical Ozone Structure Note: logarithmic scale! Modes of Energy Transfer in the Atmosphere Physical Causes of the Greenhouse Effect 7
Physical Causes of the Greenhouse Effect Physical Causes of the Greenhouse Effect Effects of Clouds on the Atmospheric Radiation Budget: SW radiation Effects of Clouds on the Atmospheric Radiation Budget: LW radiation SW A*SW SW A*SW 8
Globally Average Energy Budget Introduction to Climate Modeling Many types of climate models exist. We discuss some of the more common types, which have different levels of complexity: Zero-dimensional radiation balance models 1-dimensional radiative-convective models 2-dimensional diffusive models 3-dimensional Atmospheric General Circulation Models (AGCM) 3-D coupled atmosphere ocean models (AOGCM) zero-dimensional radiation balance model 1-dimensional radiative-convective model T = [(S/4σ)(1-A) 0.25 e (1-A) ] One-Layer Radiation Model SWin Energy SWout LWout 9
1-dimensional radiative-convective model 2-dimensional climate model 1-D Rad-Conv Model S/4 (S/4)*A Radiation Convection, in each latent wavelength fluxes band North Pole South Pole Surface: latent, sensible surface Surface 3-dimensional General Circulation Model (GCM) 3-D coupled atmosphere ocean models Atmosphere surface Ocean http://www.arm.gov/docs/documents/project/er_0441/bkground_5/figure2.html 10
Climate Feedbacks Water vapor feedback snow/ice albedo feedback IR flux/temp feedback Cloud feedback??? 11