OVERVIEW

This chapter focuses on the sun's energy which is responsible for driving the earth's physical and biological systems.

• Solar energy is the driving force for most natural phenomena at the earth's surface.
• The sun is a star of average size with a surface temperature of 6000° C generated by nuclear fusion.
• The sun emits 9% of its energy in the ultraviolet wavelengths, 41% in the visible wave lengths and 50% in the shortwave infrared wavelengths.
• The solar constant is the amount of energy received per square meter just outside the earth's atmosphere. The value is 1400 watts per square meter (1400 W/m²).
• The earth is much cooler than the sun. It therefore emits less energy and emits that energy in longer wavelengths.
• Insolation or incoming solar radiation varies with the angle of the sun above the horizon and daylength.
• Locations between 23½°N and 23½°S of the equator experience two insolation maxima per year, while locations poleward of these latitudes experience only one insolation maximum.
• Although the earth's atmosphere extends to approximately 10,000 km above the earth, 97% of the atmosphere lies within 30 km of the earth's surface.
• Pure dry air consists of 78% nitrogen and 21% oxygen by volume. Argon, CO2 and other trace gases make up the remaining 1%.
• CO2 is a very important gas due to its ability to absorb radiant heat and its role in photosynthesis.
• The ozone layer is found in the stratosphere where it absorbs ultraviolet radiation and shields the earth from its harmful effects.
• Human activity which has increased the amount of gases such as chloroflourocarbons, nitrous oxides, bromine oxides and hydrogen oxides which are depleting the ozone layer.
• For every 1% decrease in global ozone, ultraviolet radiation may increase by 2%.
• Sensible heat is the quantity of heat held by an object that can be sensed by touch, measured by a thermometer and transferred by conduction from warmer to cooler objects.
• Latent heat is energy that is absorbed and stored when a substance changes state from a liquid to a gas or from a solid to a liquid. Latent heat is transferred when water evaporates from a land or water surface and is important in moving large amounts of energy from one region to another.
• As solar radiation flows through the atmosphere, energy is scattered and absorbed by gas molecules and dust particles in the air.
• Clouds are a major factor in determining how much energy reaches the earth's surface absorbing 5 to 20% and reflecting 30 to 60% of insolation.
• The albedo of the earth's atmosphere system is 29 to 34%.
• CO2 and water vapor absorb incoming shortwave radiation and outgoing longwave radiation from the earth. They re-emit this radiation in all directions with part of it returning to the earth's surface in counterradiation.
• Net radiation is the difference between all incoming and all outgoing radiation. Although net radiation is zero for the earth as a whole, it is positive between latitude 40°N and 40°S and negative poleward of these latitudes. As a result, global and atmospheric circulation systems transport energy from lower to higher latitudes.

KEY TERMS

energy balance    equatorial zone   sensible heat      

electromagnetic   tropical zone     latent heat        

radiation         subtropical zone  diffuse radiation  

ultraviolet       midlatitude zone  albedo             

radiation         subarctic zone    counterradiation   

shortwave         arctic zone       greenhouse effect  

radiation         subantarctic      energy budget      

longwave          zone              net radiation      

radiation         antarctic zone    poleward heat      

solar constant    ozone             transfer           

visible light     stratosphere      solar power        

thermal infrared  chloroflourocarbo                    

short wave        ns                                   

infrared                                               

insolation                                             

STUDY QUESTIONS

1. In what parts of the electromagnetic spectrum does the sun emit energy?
2. What two principles apply to the electromagnetic spectrum of energy emitted from a body?
3. What is the solar constant?
4. Daily insolation is determined by what two factors?
5. How is the pattern of yearly insolation different for locations at 40° latitude compared to locations at the equator?
6. What is the impact of the tilted earth on insolation received at the poles?
7. What are the major gases that make up the earth's atmosphere, what role do each of these gases play?
8. Where is the ozone layer found? What is its role?
9. Distinguish between sensible heat and latent heat.
10. What happens to solar radiation as it passes through the atmosphere?
11. How does the earth release the energy it absorbs from the sun?
12. Define net radiation.
13. How is energy transferred from areas of surplus to areas of deficit?