A&O SCI 1 Lecture Notes - Lecture 3: Outgoing Longwave Radiation, Subtropics, Heat Flux
8 Jun 2018
School
Department
Course
Professor
Earth's Energy Balance and the Greenhouse Effect
Solar Flux
Factors influencing solar flux: Inverse-square law
• The total flux of energy transferred from one object to another varies according to the distance
between the two objects. This relationship is known as the inverse-square law
• The total energy emitted by the sun can be calculated from the Stefan-Bolzmann law
• Imagine this total energy being distributed over a sphere whose center coincides with the sun
o Lets say the radius of the sphere is d
o The total surface area of the sphere is proportional to d2
o As the radius of the sphere increases, the same energy is distributed over a larger and larger
area
o The energy per unit area, or flux, falls off of 1/d2
• The earth is about 150 million km from the sun
• The result is about 343 W/m2 of solar radiation reaching the top of earth's atmosphere on average
Angle
• The solar flux at any given location can also vary bc of the angle between the surface intercepting
the radiation and the direction of the radiation's propagation
• A more oblique angle gives a greater area over which the energy is absorbed, hence less energy
per unit area
• This is one reason the poles receive less energy than the equator
Albedo
• The earth also reflects solar radiation
• We define the reflectivity or albedo as the ratio of how much is reflected and how much is
incoming
o reflected/incident radiation
• The albedo as the ratio of reflected to incident radiation
• The albedo of the Earth is about 0.3, meaning about 30% of the incoming solar flux is reflected
back to space
o Certain regions are typically much more reflective than others
Net Solar Radiation
• Net solar radiation at the top of the earth's atmosphere = incoming minus reflect (energy flux:
W/m2)
Key Features of the planet's net solar flux distribution
• Latitude is the key determinant of how much solar radiation any given location receives
• Influence of the planet's albedo can be seen in
1. High latitudes
2. Deserts
3. Deep tropics
• Note overall importance of clouds (equator, tropics, mid latitudes)
• There is an enormous contrast between solar radiation over the summer hemisphere and the
winter pole, which receives almost none
Terrestrial Flux
Outgoing longwave radiation
• Longwave radiation is another term for terrestrial radiation. This is the outgoing terrestrial
radiation at the top of the atmosphere (W/m2), as seen from space
Document Summary
Factors influencing solar flux: inverse-square law: the total flux of energy transferred from one object to another varies according to the distance between the two objects. This relationship is known as the inverse-square law: the total energy emitted by the sun can be calculated from the stefan-bolzmann law. Albedo: the earth also reflects solar radiation, we define the reflectivity or albedo as the ratio of how much is reflected and how much is incoming reflected/incident radiation, the albedo as the ratio of reflected to incident radiation. The albedo of the earth is about 0. 3, meaning about 30% of the incoming solar flux is reflected back to space: certain regions are typically much more reflective than others. Net solar radiation: net solar radiation at the top of the earth"s atmosphere = incoming minus reflect (energy flux: Key features of the planet"s net solar flux distribution. Latitude is the key determinant of how much solar radiation any given location receives.
