Solar Flux and Flux Density Solar Flux Density Reaching Earth q Solar Luminosity (L) q Solar Constant (S) the constant flux of energy put out by the The solar energy density at the mean distance of sun Earth from the sun (1.5 x 1011 m) L = 3.9 x 1026 W S = L / (4 p d2) q Solar Flux Density (Sd) d 26 11 2 the amount of solar energy per unit area on sun = (3.9 x 10 W) / [4 x 3.14 x (1.5 x 10 m) ] a sphere centered at the Sun with a distance = 1370 W/m2 d
2 2 Sd = L / (4 p d ) W/m ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu
Solar Energy Incident On the Solar Energy Absorbed by Earth Earth
§ Solar Constant (S) = solar flux density reaching the Earth = 1370 W/m2 § Solar energy incident on the Earth = S x the “flat” area of the Earth 2 = S x p R Earth
§ Solar energy absorbed by the Earth = (received solar flux) – (reflected solar flux) 2 2 = S p R Earth – S p R Earth x A 2 q Solar energy incident on the Earth (from The Earth System) = S p R Earth x (1-A) = total amount of solar energy can be absorbed by A is the planetary albedo of the Earth, which Earth is about 0.3. = (Solar constant) x (Shadow Area) 2 = S x p R Earth ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu
1 What Happens After the Earth Blackbody Radiation Absorbs Solar Energy?
q Blackbody q The Earth warms up and has to emit radiative A blackbody is something that emits (or absorbs) energy back to the space to reach a equilibrium electromagnetic radiation with 100% efficiency at condition. all wavelength.
q The radiation emitted by the Earth is called q Blackbody Radiation “terrestrial radiation” which is assumed to be The amount of the radiation emitted by a like blackbody radiation. blackbody depends on the absolute temperature of the blackbody.
ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu
Planetary Energy Balance Energy Emitted from Earth
§ Energy emitted by Earth = Energy absorbed by Earth
4 2 2 sTe x (4p R Earth ) = S p R Earth x (1-A) § The Stefan-Boltzmann Law sT 4 = S/4 * (1-A) The energy flux emitted by a blackbody e is related to the fourth power of the body’s = 1370/4 W/m2 * (1-A) absolute temperature = 342.5 W/m2 * (1-A) F = sT4 where s is 5.67x10-8 W/m2/K = 240 W/m2 § Energy emitted from the Earth (from Global Physical Climatology) = (blackbody emission) x (total area of Earth) § Earth’s blackbody temperature 4 2 = (sTe ) x (4p R Earth ) Earth’s surface temperature Te = 255 K (-18C) (from The Earth System) TS = 288 K (15C)
greenhouse effect (33C) !! ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu
2 Greenhouse Effect Different Wavelengths of Solar and Earth’s Radiation Greenhouse Atmosphere Normalized Planck Function Planck Function T 4 sunlight S/4 * (1- s A A) longwave
sT heat 4 S 4 shortwave sTA
§ allow sunlight to come in At the top of the atmosphere: S/4*(1-A) = sT 4 è T =T = 255K § trap heat inside the house A A e
For Earth’s surface: (from The Earth System) 4 4 S/4*(1-A) + sTA = sTS
è TS =1.19TA= 303K
ESS200A ESS200A Prof. Jin-Yi Yu (from Climate System Modeling) Prof. Jin-Yi Yu
Greenhouse Gases Where Does the Solar Energy Go?
Incoming solar energy (100)
§ 70% absorbed
25% 45% by Earth’s surface (ocean + land) 25% by the atmosphere and clouds
§ 30% reflected and scattered 45% back
(from NCAR/COMET website) 20% by clouds 6% by the atmosphere 4% by surface
ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu
3 Important Roles of Clouds In Where Is Earth’s Radiation Emitted From? Global Climate Radiation back to Space (70 Units)
§ 70 (units) radiation back to space 66% by the atmosphere 4% by surface (through clear sky) (from The Earth System) § Greenhouse emission (back to surface) 88% (of solar radiation)
(from The Earth System)
ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu
How Do Atmosphere and Ocean Transport Polarward Energy Transport Heat?
Annual-Mean Radiative Energy Polarward Heat Flux Atmospheric Circulation Ocean Circulation
(from USA Today)
The atmosphere dominates the Polarward heat flux is needed to polarward heat transport at transport radiative energy from middle and high latitudes. The the tropics to higher latitudes ocean dominates the transport at lower latitudes.
15 (top from The Earth System) (1 petaWatts = 10 W) ESS200A ESS200A (figures from Global Physical Climatology) Prof. Jin-Yi Yu (bottom from USGCRP) Prof. Jin-Yi Yu
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