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?