The Greenhouse Effect R Electromagnetic EM radiation radiation

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

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

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?

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

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). 1) 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.

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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?

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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?

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

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

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

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

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

(No Atmosphere Case) Absorbed = Emitted = Earth,

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

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

Earth’s atmosphere absorbs light at most wavelengths.

Selective Absorption in the Atmosphere

Greenhouse Gases are… ¥ …“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)

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

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.

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Cloudy Sky Contemplation § Why is the cloudy sky temperature relatively flat? § How does clear sky temperature get both hotter and colder than the cloudy sky temperature?

Greenhouse Process Incoming Solar Earth’s Surface Emits Infrared Radiation

Greenhouse Process Greenhouse Gases 1) Absorb IR

Greenhouse Process Greenhouse Gases 1) Absorb IR 2) Emit IR

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

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

The Greenhouse Effect Summary HGs absorb IR emitted by Earth’s Surface G 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.