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