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Ch Solar Energy and the Atmosphere

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1 Ch. 23.2 Solar Energy and the Atmosphere

2 Radiation Radiation—all forms of energy that travel through space as waves. Includes visible light, x-rays, radio waves, uv radiation, and more. The difference in types of radiation is their wavelength. The electromagnetic spectrum is made up of electromagnetic waves of all different wavelengths.


4 Almost all energy from the sun reaches earth as electromagnetic waves (some is in particle form).
Solar radiation must pass through the atmosphere before reaching the earth’s surface.


6 Atmosphere’s possible effect on solar radiation:
Shorter wavelengths absorbed by oxygen and nitrogen in upper atmosphere (mesosphere and thermosphere). UV rays absorbed by oxygen in stratosphere to form ozone. Longer wavelengths (visible and infrared) reach lower atmosphere.

7 Most infrared radiation is absorbed by carbon dioxide and water vapor in troposphere.
Very little visible light absorbed.

8 Scattering Gas and particles in the atmosphere reflect and bend light waves in all directions, without changing their wavelengths. Some radiation scattered back into space. Because of scattering, sunlight reaches earth from all directions. Short wavelengths (blue) are most easily scattered, so sky appears blue.

9 When sun is low on horizon, more blue than red is scattered (more blue wavelength photons eventually end up being scattered back into space), so more red light wavelengths reach the surface, so the sun appears red.

10 Reflection Only 20% of solar radiation is absorbed by the atmosphere.
30% is scattered back to space or reflected by clouds, or the earth’s surface. Remaining 50% is absorbed by earth’s surface. Dark colored surfaces absorb more…Light colors reflect more. (Table 23.1)

11 Since 30% of solar radiation that reaches the earth is reflected or scattered back to space, earth has an average reflectivity of 30%. The albedo of earth is 0.3. Albedo of the moon is 0.7 (70% of light is reflected).

12 Absorption and Infrared Energy
Radiation absorbed by earth’s surface is re-emitted as longer wavelength infrared rays. Some gases in the lower atmosphere absorb the longer infrared rays, thus trapping heat and warming the air. The process of trapping and warming is known as the Greenhouse Effect.

13 Concern that excessive release of greenhouse gases by humans may lead to global warming.

14 Variations in Temperature
Radiation heats the earth unequally, depending on several factors… Latitude Elevation Nearness to bodies of water. Influence of wind patterns. Daily and seasonal delays (2.00 p.m., and late July).

15 Conduction and Convection
In conduction, the energy and movement of atoms or molecules is transferred to adjacent atoms or molecules, which transfers heat. Solids are good conductors, but not gases, because gas molecules are much further apart. Lower atmosphere is heated through conduction by contact with the warm surface.

16 Convection is the transfer of heat by the movement of liquids or gases..
In the atmosphere, uneven heating results in warm air rising, and cold air sinking. Rising warm air creates low pressure; sinking cold air creates high pressure. Air always moves from high to low pressure, creating wind.

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