8: Infrared (Longwave) Radiation
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Energy Absorbed (formula)
Energy absorbed = Area x solar flux x (1 -albedo) = (pi r2) x (Si) x (1 - alpha)
Solar flux 1) Define 2) Denoted with 3) Measure with
1) Amount of radiation per unit area 2) Si 3) Pyranometer
Energy Emitted (formula)
Energy emitted = Surface area x emissivity x constant x T^4 = 4 pi r2 x e x o x T^4 (where e = ~0.94 - land surface) (4 pi r2 = energy emitted across the globe so total surface area Stefan-Boltzmann equation with added e
energy emitted = energy absorbed equilibrium
energy emitted = energy absorbed (4 pi r2)(e)(omega)(T^4) = (pi r2)(Si)(1-alpha) T^4 = Si)(1-alpha)/ (4)(e)(omega)
If earth’s temperature was solely a function of radiation absorbed & reflected at the surface, 1) What temperature would it be? 2) Where does the additional source of heat come from
1) 255 K (-18 *C) 2) Interactions of the outgoing infrared radiation with the atmosphere (GHGs)
Infrared images on: 1) Cloud temperature 2) Land
1) Brighter the white, the cooler the cloud, the higher it is 2) Land is warmer so it is dark
Measuring infrared radiation 1) shortwave 2) longwave
1) easy to measure as anything that is hot emits and wont be emitting infrared 2) much more difficult as everything (>0 K) emits infrared
Shortwave radiation 1) Absorption 2) Emitted 3) Scattering 4) Reflection
1) Weak (except for UV) 2) Very little to none (due to air temperature) 3) By dust & aerosols 4) By clouds
Longwave radiation 1) Absorption 2) Emitted 3) Reflection
1) Significant (Due to GHGs) 2) Significant (due to airs temperature) 3) Insignificant (longwave emitted from everything at a similar range)
Radiation 1) Formula What denotes 2) T 3) r 4) a
1) T + r + a = 1 2) Transmissivity 3) Reflectivity (only shortwave radiaiton) 4) Absorptivity
Radiation
Greenhouse Effect (closed system)
No convection, advection or clouds Water vapor trapped Shortwave radiation penetrates through glass Emitted longwave radiation is trapped
Greenhouse Effect (Atmospheric) 1) Is there convection, advection or clouds? 2) Transmissivity (higher or lower for shortwave) 3) Absorptivity (higher or lower for shortwave)
1) Convection, advection & clouds 2) Transmissivity of atmos to shortwave is much higher than longwave 3) Absorptivity of atmos to longwave is much higher than shortwave
Greenhouse Effect 1) Where does it depend on 2) Which greenhouse gas/es has the longest window in which to absorb long wavelengths 3) Which greenhouse gas/es has the shortest window in which to absorb long wavelengths
1) Troposphere 2) H2O (Most important GHG) 3) CO2 & O3 (Ozone) but mainly in stratosphere, so insignificant