HKDSE Geography/M7/Radiation Budget
The earth's solar radiation budget is made up of two components: Incoming radiation and outgoing radiation.
Incoming solar radiation
[edit | edit source]What is insolation? Simple.
![](http://upload.wikimedia.org/wikipedia/commons/thumb/2/25/Electromagnetic-Spectrum.svg/200px-Electromagnetic-Spectrum.svg.png)
Energy transmitted from the sun to the earth is solar radiation. They are in the form of electromagnetic waves. The type of radiation depends on the electromagnetic spectrum. Around 99% of the insolation is belongs to the middle range of the electromagnetic spectrum: ultraviolet, visible light and infrared.
Solar radiation is also known as short-wave radiation. There is also long-wave radiation, which we will look at later.
Solar radiation is measured in Watts per square metre (W/m2).
Surplus and Deficit
[edit | edit source]When incoming radiation exceeds outgoing radiation, the net radiation is positive and a surplus occurs. When outgoing radiation exceeds incoming radiation, the net radiation is negative and a deficit occurs.
Low latitudes tend to have surplus budgets and high latitudes tend to have deficits. This will be explored later.
Transfer processes
[edit | edit source]Short-wave radiation processes:
- After insolation enters the atmosphere, it may be:
- Reflected and scattered by the clouds
- Reflected by the atmosphere
- Absorbed by the atmosphere
- After it reaches the ground,
- It can be reflected by the earth's surface.
- It can be absorbed by the earth's surface.
Long-wave radiation
- After heat energy is absorbed by the earth's surface,
- It can be re-radiated back to the atmosphere. This is long-wave radiation or terrestrial radiation.
- The terrestrial radiation will then go these processes:
- It may be radiated directly into space.
- It may be radiated into the atmosphere.
- Some of it will be radiated into space.
- Some of it will be trapped in the atmosphere by greenhouse gases. This is the greenhouse effect.
- The heat trapped by greenhouse gases will be re-radiated back to the earth's surface as counter-radiation.
- It may return to the atmosphere through conduction, convection and evaporation.