The Energy In Sector

The Energy In Sector

Figure 1. A very simple STELLA model of Earth’s climate system.  The three colored sectors show the parts of the model that keep track of the energy coming in to the Earth from the Sun, the energy leaving the Earth through emitted heat, and the average surface temperature of the Earth.

David Bice

The Energy In sector (yellow in Fig. 1 above) controls the amount of insolation absorbed by the planet.  The Solar Constant is not really a constant, but it does tend to stay close to a value of 343 Watts/m² (think of about six 60 Watt light bulbs shining down on a patch of ground 1 meter on a side — this is what we get from the Sun).  This is then multiplied by (1 – albedo) and then the surface area of the Earth giving a result in Watts (which is a measure of energy flow and is equal to Joules per second).  In the form of an equation, this is:

$${\text{E}}_{in}\text{=S}\times \text{A}\times \text{(1-}\alpha \text{)}$$

S is the Solar Constant (343 W/m²), A is surface area, and α is the albedo (0.3 for Earth as a whole).

This is the equation E_in=S×A×(1-α)