Peralta Colleges, Physical Geography
Rita D. Haberlin, Instructor
SOLAR RADIATION STUDY GUIDE
Assigned reading: Elemental Geosystems, Christopherson, Chapter 3, Pages 75-87
Solar Radiation Tutorial (In the Solar Radiation Web Learning Module)
Web Learning Module: Solar Radiation
- The sun is a vast thermonuclear engine fusing hydrogen into helium. The fusion process generates intense energy that travels outwards as electromagnetic radiation. Electromagnetic radiation from the sun takes the form of visible light (41%), ultra violet, X rays, and gamma rays (9%), and shortwave infra red energy (50%).
- A radiation balance exists between the sun's shortwave radiation (0.2-5 microns) and the earth's longwave radiation (3-50 microns). Shortwave radiation from the sun does not readily heat gases but does heat the solid earth. Longwave radiation is emitted from the earth's surface into the atmosphere. (Note: 1 micron is 1/10,000th of a centimeter.)
- The heat energy received by a surface perpendicular to the sun's rays, outside the atmosphere would be a relatively constant 1400 watts per square meter. This is called the solar constant.
- Insolation refers to incoming solar radiation. The total daily insolation at a place on the earth's surface is determined by: a) the angle of the sun's rays, b) the amount of time a place is exposed to the sun's rays and c) the amount of clouds, dust, and water vapor in the atmosphere. Insolation also varies with latitude and the seasonal changes produced by the tilt of earth’s axis in its orbit around the sun.
- Some solar radiation is intercepted as it passes through the atmosphere. About 50% of the sunlight reaching the upper atmosphere actually warms the earth's surface. Some 30% is lost due to reflection from clouds, and the earth’s surface and scattering off dust and gas molecules. Absorption by gas molecules, dust, and clouds accounts for another 20% loss.
- The atmosphere is heated from below by longwave radiation, sensible heat, and the release of latent heat. Sensible heat includes conduction, heat transfer by direct contact and convection where heated air moves as a vertical current. The atmosphere is also warmed directly by solar radiation that is absorbed by water droplets in clouds and dust particles.
- Some of the earth's radiation is temporarily retained in the lower atmosphere by carbon dioxide and water vapor. These gases are good heat absorbers and also good radiators. This process that returns radiation toward the earth is called the greenhouse effect. Without this source of heat the earth would be a much colder planet.
- For the earth as a whole, insolation must equal longwave radiation to space. However, low latitudes (0 - 40° North and South) receive more insolation than they emit to space (energy surplus). Higher latitudes (40 - 90° North and South) emit more radiation to space than they receive (energy deficit).
- A global radiation balance is maintained by the poleward transfer of heat from regions of energy surplus to regions of energy deficit. This heat transfer takes place as ocean currents, winds (atmospheric circulation), and latent heat move from low to high latitudes.
- People's activities may alter the global radiation balance by changing the chemistry of the atmosphere and the dustiness of the planet.
- What is the source of the sun's energy? Describe the forms of electromagnetic radiation emitted from the sun.
- Define radiation balance. How does solar radiation differ from earth radiation?
- Define the solar constant.
- What is insolation? What are the factors that determine the amount of insolation.
- How much sunlight reaches the earth's surface and how is it intercepted in the atmosphere.
- How is the atmosphere is heated?
- Define the greenhouse effect. What are some greenhouse gases?
- Describe the relationship between insolation and longwave radiation in the low latitudes and high latitudes.
- Describe how a global radiation balance is maintained by poleward heat transport.
- How do people’s activities affect the global radiation balance?
DEFINE THE FOLLOWING TERMS:
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Created by Rita D. Haberlin, Geography Professor
Peralta Community College District
333 East Eighth Street
Oakland, CA 94606
This Geography Site Is Maintained By Patricia A. Kulda
Last Update July 14, 2010