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The Greenhouse Effect

Electromagnetic (EM) radiation, radiation processes “Clear Sky” Exercise Earth-Sun System Greenhouse Gases “Cloudy Sky” Exercise. The Greenhouse Effect. Background Information. Electromagnetic (EM) radiation Solar and Terrestrial Emission Radiation Processes and Interactions

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The Greenhouse Effect

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  1. Electromagnetic (EM) radiation, radiation processes • “Clear Sky” Exercise • Earth-Sun System • Greenhouse Gases • “Cloudy Sky” Exercise The Greenhouse Effect

  2. Background Information • Electromagnetic (EM) radiation • Solar and Terrestrial Emission • Radiation Processes and Interactions • Water Vapor is a Greenhouse Gas (selective absorpotion)

  3. Central Project Question Knowing that water vapor is a potent greenhouse gas, what do you expect is the short-term effect of cloud cover on your local temperature?

  4. Electromagnetic (EM) radiation, radiation processes • “Clear Sky” Exercise • Earth-Sun System • Greenhouse Gases • “Cloudy Sky” Exercise • Earth vs Moon The Greenhouse Effect

  5. Clear Sky Anticipation Questions For a weather station located at Des Moines, Iowa , consider the following questions regarding the diurnal cycle during both winter (January) and summer (July). • Why does temperature change through the day? 2) Assuming a cloudless day, plot your expectations for the diurnal cycle of temperature using the blank template figure.

  6. Hour of Day Hour of Day

  7. Anticipation Questions (continued…) Diurnal cycle during both winter (January) and summer (July) at Des Moines Iowa. 3) Indicate the time of sunrise and sunset in your figure. 4) What, specifically, causes temperature to increase or decrease? 5) How do summer and winter differ? Why?

  8. Hour of Day Hour of Day

  9. Anticipation Questions (summary) • Diurnal cycle during both winter (January) and summer • (July) at Des Moines Iowa. • Indicate the time of sunrise and sunset in your figure. • What, specifically, causes temperature to increase or decrease? • How do summer and winter differ? Why?

  10. Realization Data Source:Airport at Des Moines, IA from 1945-2004 (NCDC Surface Airways) Observation Variables:Temperature and cloud ceiling height (the height of the lowest cloud layer, if present) • Methodology: • Sort data and select only “clear sky” conditions • Compute the average diurnal cycle • Repeat for both January and July data

  11. Hour of Day Hour of Day

  12. Clear Sky Contemplation • Why does temperature change through the day? • How does temperature decrease? • How do summer and winter differ?

  13. Electromagnetic (EM) radiation, radiation processes • “Clear Sky” Exercise • Earth-Sun System • Greenhouse Gases • “Cloudy Sky” Exercise • Earth vs Moon The Greenhouse Effect

  14. Radiation: Fundamental Principles • All objects emit EM radiation; the wavelength and energy emitted depends on the object’s temperature • As Temperature increases, • total emission increases • As Temperature increases, • wavelength of peak emission decreases

  15. Solar and Terrestrial Radiation UV | Visible | IR NOTE: Log Scale! Sun Earth

  16. (No Atmosphere Case) = Earth, Absorbed = Emitted

  17. Solar Radiation Terrestrial Radiation “Radiative Equilibrium” Incoming = Outgoing Stable Temperature

  18. Electromagnetic (EM) radiation, radiation processes • “Clear Sky” Exercise • Earth-Sun System • Greenhouse Gases • “Cloudy Sky” Exercise • Earth vs Moon The Greenhouse Effect

  19. Earth’s atmosphere absorbs light at most wavelengths.

  20. Selective Absorption in the Atmosphere

  21. …“transparent” for sunlight • …only partially transparent to Infrared Radiation (…from Earth’s Surface) • … “warmed” via radiation (However, sensible heat and convection also “warm” the atmosphere) Greenhouse Gases are…

  22. Electromagnetic (EM) radiation, radiation processes • “Clear Sky” Exercise • Earth-Sun System • Greenhouse Gases • “Cloudy Sky” Exercise • Earth vs Moon The Greenhouse Effect

  23. Cloudy Sky Anticipation Questions Diurnal cycle during both winter (January) and summer (July) at Des Moines Iowa. 1) How might temperature differ between clear and cloudy sky conditions? 2) Draw your expectations on the figure provided, labeling the clear and cloudy sky lines.

  24. Hour of Day Hour of Day

  25. Hour of Day Hour of Day

  26. Cloudy Sky Contemplation • Why is the cloudy sky temperature relatively flat? • How does clear sky temperature get both hotterand colder than the cloudy sky temperature?

  27. Incoming Solar Earth’s Surface Emits Infrared Radiation Greenhouse Process

  28. Greenhouse Process • Greenhouse Gases • Absorb IR

  29. Greenhouse Process • Greenhouse Gases • Absorb IR • Emit IR

  30. Greenhouse Process NET EFFECT: Earth’s surface Warmed by TWO Heating sources

  31. Greenhouse Process What if we add more Greenhouse Gases?? TWO Heating sources

  32. Summary • GHGs absorb IR emitted by Earth’s Surface • The gases also emit IR back to the surface, providing an additional heating source. • An example of this effect is the relative warmth of cloudy nights. • Additional GHGs will increase surface temperature in the same way as enhanced cloud cover. The Greenhouse Effect

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