Lecture 2: Global Energy Cycle
Solar Luminosity (L) | |
the constant flux of energy put out by the sun | |
L = 3.9 x 1026 W | |
Solar Flux Density (Sd) | |
the amount of solar energy per unit area on a sphere centered at the Sun with a distance d | |
Sd = L / (4 p d2) W/m2 | |
Solar Flux Density Reaching Earth
Solar Constant (S) | |
The solar energy density at the mean distance of Earth from the sun (1.5 x 1011 m) | |
S = L / (4 p d2) | |
= (3.9 x 1026 W) / [4 x 3.14 x (1.5 x 1011 m)2] | |
= 1370 W/m2 |
Solar Energy Incident On the Earth
Solar energy incident on the Earth | |
= total amount of solar energy can be absorbed by Earth | |
= (Solar constant) x (Shadow Area) | |
= S x p R2Earth |
Solar Energy Absorbed by Earth
What Happens After the Earth Absorbs Solar Energy?
The Earth warms up and has to emit radiative energy back to the space to reach a equilibrium condition. | |
The radiation emitted by the Earth is called “terrestrial radiation” which is assumed to be like blackbody radiation. |
Blackbody | |
A blackbody is something that emits (or absorbs) electromagnetic radiation with 100% efficiency at all wavelength. | |
Blackbody Radiation | |
The amount of the radiation emitted by a blackbody depends on the absolute temperature of the blackbody. |
Different Wavelengths of Solar and Earth’s Radiation
Where Does the Solar Energy Go?
Where Is Earth’s Radiation Emitted From?