B.2 Greenhouse Effect Flashcards
Emissivity (e)
How close to a black body an object is
Emissivity formula not in book
power radiated per unit area of a object / power radiated per unit area of a black body at the same temperature.
Max emissivity
1.0 for a black body
Albedo (a)
Proportion of incident radiation that is reflected/scattered
a = 1
All incident radiation is reflected
a=0
All incident radiation is absorbed
Earth’s albedo
Changes daily but usually 0.3
What does Earth’s albedo depend on?
Cloud formation and latitude
Solar constant
The amount of solar energy that falls per second on an area of 1m^2 above the earths atmosphere (average value 1360Wm-2)
Why is the amount of power that arrives per m^2 on earth much lower than the solar constant?
Due to the radiation absorbed by the atmosphere/reflected by the clouds
What is the proportion of the radiation that reaches the earths surface?
It depends on weather but typically 45% of that falling on the upper atmosphere
Why do different parts of the Earth’s surface receive different amounts of solar radiation per m^2?
They are at different latitudes so receive different amounts of solar radiation due to variations in the angle at which the Sun’s rays strike the surface and the thickness of the atmosphere through which the radiation travels.
Give two examples of why the radiation received would be less?
Longer distance needing to travel through atmosphere, shallower angle means energy is more spread out
Why is the average intensity incident to Earth’s upper atmosphere 1360Wm^-2 while the average intensity incident to Earth’s entire upper atmosphere 340 Wm^-2?
Upper atmosphere - earth viewed from sun as a disc and so energy is 1360xpiR^2
Entire atmosphere - energy is spread out over the surface of the atmosphere (1360piR^2/4piR^2
Greenhouse effect
Earth’s atmosphere warming the planet’s surface
Sun’s radiation onto Earth
Sun’s incoming radiation is mostly in the ultraviolet and visible regions, which is absorbed and causes the earth’s surface to heat up. Because of the temperature, infrared light is reflected.
Greenhouse gas examples
Methane, water vapour, carbon dioxide, nitrous oxide
How do greenhouse gases increases Earth’s temperature?
The reflected infrared light is absorbed by greenhouse gases and is reflected in all directions. Some is absorbed by the surface, further heating up the earth.
Why do greenhouse gases absorb infra-red radiation?
Frequency of the radiation is the same as the natural frequency (molecular energy level) as the green house gas particles vibrations.
Resonant frequency
Natural frequency
Resonance
Absorption of radiation at the same frequency
Enhanced greenhouse effect
The increase of greenhouse gases in the atmosphere due to human activity
Solar constant units
Wm-2
