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Heating The Earth


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Heating The Earth

  1. 1. Heating the Earth Annual solar energy falling on United States contains 2000X more energy than annual coal production.
  2. 2. Solar Energy <ul><li>Most of the environmental processes acting near the surface of the Earth derive their energy from exchanges of heat between the Earth and the atmosphere above. </li></ul><ul><li>Much of this heat comes from radiant energy initially provided by the absorption of solar radiation. </li></ul><ul><li>The absorbed energy is used to warm the atmosphere, evaporate water, warm the surface along with a host of other processes. </li></ul>
  3. 3. Solar Energy <ul><li>Temperature at surface of sun is 6000 ° C. </li></ul><ul><li>Some if this thermal energy is converted to radiant energy. </li></ul><ul><li>The top of the earth’s atmosphere receives the types of shortwave radiation from the sun: </li></ul><ul><ul><li>Ultraviolet (7%) </li></ul></ul><ul><ul><li>Visible (43%) </li></ul></ul><ul><ul><li>Infrared (50%) </li></ul></ul><ul><li>The most intense radiation is visible. </li></ul>
  4. 4. Radiation from the Sun and Earth
  5. 5. Insolation <ul><li>Insolation is the amount of solar radiation reaching the earth’s surface. It varies because: </li></ul><ul><ul><li>Solar radiation interacts with the earth’s atmosphere; and </li></ul></ul><ul><ul><li>There are changes in the orientation between the Earth and the Sun. </li></ul></ul><ul><li>On average, the Earth receives 1368 W/m 2  of solar radiation at the outer edge of the atmosphere, called the &quot;solar constant&quot;. </li></ul>
  6. 6. Insolation and the Atmosphere <ul><li>As solar radiation travels through the earth’s atmosphere, three things can happen to the radiation: </li></ul><ul><ul><li>Scattering </li></ul></ul><ul><ul><li>Reflection </li></ul></ul><ul><ul><li>Absorption </li></ul></ul>
  7. 7. Scattering <ul><li>Radiation &quot;bumps&quot; into molecules and produces a large number of weaker waves traveling in many different directions but mainly forward. </li></ul><ul><li>Blue light the most scattered length in sky (hence the blue sky) </li></ul><ul><li>Scatter radiation is called Diffused Light </li></ul>
  8. 8. Reflection <ul><li>Reflected light bounces back from a surface at the same angle at which it strikes that surface and with the same intensity. </li></ul><ul><li>Albedo is the fraction of radiation that is reflected by a substance. </li></ul><ul><li>Expressed as a percentage (see next slide) </li></ul>
  9. 9. Albedo
  10. 10. Absorption <ul><li>Absorption a process in which solar radiation is retained by a substance and converted into Thermal Energy . </li></ul><ul><li>The creation of heat energy also causes the substance to emit its own radiation </li></ul><ul><li>In general, the absorption of solar radiation by substances in the Earth's atmosphere results in temperatures that get no higher than 1800° Celsius. </li></ul><ul><li>Bodies with temperatures at this level or lower would emit their radiation in the long wave band. </li></ul>
  11. 11. Absorption of Incoming Solar Radiation by Atmosphere <ul><li>O 2 and O 3 absorbs UV Radiation </li></ul><ul><li>CO 2 , N 2 , and H 2 0 absorb Infrared Radiation </li></ul><ul><li>Visible Radiation is transparent to the atmospheric gases </li></ul>
  12. 12. Average distribution of incoming solar radiation
  13. 13. Average distribution of incoming solar radiation <ul><li>5% Scatted by Atmosphere </li></ul><ul><li>20% Absorbed by Atmosphere </li></ul><ul><li>20% Reflected by Atmosphere </li></ul><ul><li>5% Reflected by Surface </li></ul><ul><li>50% Absorbed by the surface of the earth </li></ul><ul><ul><li>Mainly visible (shortwave) radiation strikes the surface. </li></ul></ul><ul><ul><li>Solar radiation is transformed into thermal molecular motion or thermal energy at the surface. </li></ul></ul>
  14. 14. Surface – Atmosphere Heat Exchange <ul><li>Thermal Energy is transferred from the surface into the atmosphere in three ways: </li></ul><ul><li>1) Evaporation </li></ul><ul><ul><li>Water evaporates at the surface and then condenses to form clouds which releases latent heat </li></ul></ul><ul><li>2) Conduction/Convection </li></ul><ul><ul><li>Warm surface air will rise to higher altitudes </li></ul></ul><ul><li>3) Terrestrial Radiation </li></ul><ul><ul><li>Due to the increase in temperature, the surface reemits infrared (long wave) radiation. </li></ul></ul><ul><ul><li>MOST COMMON </li></ul></ul>
  15. 15. Radiation from the Sun and Earth
  16. 16. Atmospheric Radiation <ul><li>The atmosphere absorbs radiation from both the incoming solar radiation and the outgoing terrestrial radiation. </li></ul><ul><li>Higher percentage of this radiation is terrestrial (long wave) radiation. </li></ul><ul><li>Because the atmosphere is largely transparent to solar (shortwave) radiation but more absorptive of terrestrial (long wave) radiation, the atmosphere is heated from the ground up, instead of visa versa. </li></ul>
  17. 17. Outgoing Terrestrial Radiation <ul><li>CO 2 , N 2 , and H 2 0 in the atmosphere absorb most of the terrestrial radiation. </li></ul><ul><li>Note the atmospheric window that allows some (6%) of the terrestrial radiation to escape back into space </li></ul>
  18. 18. Outgoing Terrestrial Radiation <ul><li>H 2 O, CO 2 , CH 4, N 2 , (plus other manmade greenhouse gasses such as CFCs) in the atmosphere absorb most of the outgoing infrared terrestrial radiation. </li></ul><ul><li>These molecules become excited, increase in temperature and reemit long wave radiation back to the surface and out into space. </li></ul><ul><li>This is called the “Greenhouse Effect.” </li></ul>
  19. 19. The Greenhouse Effect
  20. 20. Atmospheric Greenhouse Effect Step 1 <ul><li>Solar shortwave radiation is absorbed by the earth’s surface </li></ul>
  21. 21. <ul><li>Earth's surface radiates long wave radiation which is absorbed by the greenhouse gasses. </li></ul>Atmospheric Greenhouse Effect Step 2
  22. 22. <ul><li>Greenhouse gasses reradiated some of the energy earthward, thus trapping heat in the lower atmosphere. </li></ul>Atmospheric Greenhouse Effect Step 3
  23. 23. Atmospheric Greenhouse Effect <ul><li>The absorption of outgoing terrestrial infrared radiation increase the surface temperature of the atmosphere about 30 ° C. </li></ul><ul><li>The average surface temperature is about 15 ° C. </li></ul><ul><li>If we did not have greenhouse gasses, the surface temperature of the earth would be about -15 ° C! </li></ul>
  24. 24. Goldilocks' Effect <ul><li>On Mars, the atmosphere is too thin and the greenhouse effect does not trap enough heat </li></ul><ul><li>On Venus, the atmosphere is too thick and the greenhouse effect traps too much heat </li></ul>Too Cold Just Right Too Hot 450 °C 15 °C -50 °C
  25. 25. Variations in Insolation <ul><li>Variations on insolation also occur due to changes in the orientation between the earth and the sun. </li></ul><ul><li>These changes are based on: </li></ul><ul><ul><li>Latitude </li></ul></ul><ul><ul><li>Time of Day </li></ul></ul><ul><ul><li>Time of Year </li></ul></ul>
  26. 26. Latitude and Insolation <ul><li>A significant impact on insolation is the thickness of the atmosphere on depletion of a beam of light. </li></ul><ul><li>As the amount of atmosphere through which the beam passes increases, the greater the chance for reflection and scattering of light, thus reducing insolation at the surface. </li></ul><ul><li>Due to the curvature of the Earth, a beam of light striking the Equator passes through less atmosphere than one at a higher latitude. </li></ul>
  27. 28. Latitude and Insolation <ul><li>The lower the latitude, the less the path length, the higher the insolation. </li></ul><ul><li>Thus insolation is greater at the equator (0 ° latitude ) than at the poles (90 ° latitude ). </li></ul>
  28. 29. Daily and Seasonal Changes in Insolation
  29. 30. Sun (Azimuth) Angle <ul><li>The constant tilt causes changes in the angle that a beam of light makes with respect to a point on Earth during the year, called the &quot; sun angle “ or “Azimuth”. </li></ul><ul><li>The most intense incoming solar radiation occurs where the sun's rays strike the Earth at the highest angle. </li></ul>
  30. 31. Sun (Azimuth) Angle <ul><li>As the sun angle decreases, the beam of light is spread over a larger area and decreases in intensity. </li></ul><ul><ul><li>During the summer months the Earth is inclined toward the Sun yielding high sun angles. </li></ul></ul><ul><ul><li>During the winter, the Earth is oriented away from the Sun creating low sun angles.  </li></ul></ul>
  31. 32. Seasons and Sun (Azimuth) Angle <ul><li>Sun angle for Peoria (40 ° N) at the summer solstice and winter solstice. </li></ul><ul><li>Note how the angle changes seasonally. </li></ul>
  32. 33. Earth Revolution and Rotation <ul><li>Earth revolves around the Sun once every 365 1/4 days. </li></ul><ul><li>The elliptical orbit of the earth varies from 147.5 million kilometers on January 3 called &quot; perihelion &quot;, to 152.5 million kilometers on July 4 called &quot; aphelion &quot; for an average earth-sun distance of 150 million kilometers. </li></ul><ul><li>The elliptical path causes only small variations in the amount of solar radiation reaching the earth. </li></ul>
  33. 34. Earth Revolution and Rotation
  34. 35. Axial Tilt <ul><li>The Earth's axis is tilted 23 1/2 degrees from being perpendicular to the plane of the ecliptic. </li></ul><ul><li>The axis of rotation remains pointing in the same direction as it revolves around the Sun. </li></ul><ul><li>As a result, the Earth's axis of rotation remains parallel to its previous position as it orbits the sun. </li></ul>
  35. 36. Axial Tilt
  36. 37. The Reason for the Seasons <ul><li>The tilt of the Earth is the reason the Northern and Southern Hemisphere have opposite seasons. </li></ul><ul><li>Summer occurs when a hemisphere is tipped toward the Sun and winter when it is tipped away from the Sun. </li></ul><ul><li>Day length changes through the year as the orientation of the Earth to the Sun changes </li></ul>
  37. 38. The Reason for the Seasons
  38. 39. The Reason for the Seasons <ul><li>Summer solstice (Northern Hemisphere) </li></ul><ul><ul><li>June 21-22 </li></ul></ul><ul><ul><li>Sun's vertical rays are located at the Tropic of Cancer (23½º N latitude) </li></ul></ul><ul><ul><li>24 hours daylight at the north pole; 12 hours at the equator; and 0 hours at the south pole. </li></ul></ul><ul><li>Winter solstice (Northern Hemisphere) </li></ul><ul><ul><li>December 21-22 </li></ul></ul><ul><ul><li>Sun's vertical rays are located at the Tropic of Capricorn (23½º S latitude) </li></ul></ul><ul><ul><li>24 hours daylight at the south pole; 12 hours at the equator; and 0 hours at the north pole. </li></ul></ul>
  39. 40. The Reason for the Seasons <ul><li>Autumnal equinox (Northern Hemisphere) </li></ul><ul><ul><li>September 22-23 </li></ul></ul><ul><ul><li>Sun's vertical rays are located at the Equator (0º latitude) </li></ul></ul><ul><ul><li>12 hours daylight at all latitudes </li></ul></ul><ul><li>Spring equinox (Northern Hemisphere) </li></ul><ul><ul><li>March 21-22 </li></ul></ul><ul><ul><li>Sun's vertical rays are located at the Equator (0º latitude) </li></ul></ul><ul><ul><li>12 hours daylight at all latitudes </li></ul></ul>
  40. 41. Daily and Seasonal Changes in Insolation
  41. 42. Insolation and Surface Orientation <ul><li>Dues to changes in insolation, the amount of radiation a vertical and horizontal surface receives changes seasonally. </li></ul><ul><li>Note the inverse relationship on the graph. </li></ul><ul><li>This will be important when we discuss passive solar design. </li></ul>