1. Lecture 3: Radiation and Earth’s Atmosphere EarthsClimate_Web_Chapter.pdfEarthsClimate_Web_Chapter.pdf, p. 1-5 For more advanced reading materials, please see http://www.geo.utexas.edu/courses/387h/ScheduleGPC_detail.htm http://www.geo.utexas.edu/courses/387h/ScheduleGPC_detail.htm

2. Earth’s Atmosphere 1. What is it? A thin gaseous envelope around the planet. 2. Composition Today’s atmosphere: nitrogen (78%), oxygen (21%), other (1%) – trace gases! Nitrogen, oxygen, argon, water vapor, carbon dioxide, methane, and most other gases are invisible. Clouds are not gas, but condensed vapor in the form of liquid droplets or ice particles. Ground based smog, which is visible, contains reactants of nitrogen and ozone. 3. Structure Four layers: Troposphere (overturning) (overturning) Stratosphere (stratified) (stratified) From surface to 8-18 km From surface to 8-18 km From troposphere top to 50 km From troposphere top to 50 km Mesosphere Thermosphere Blue sky!

3. The Structure of Earth’s Atmosphere 1. Four layers defined by temperature 2. Importance to climate and climate change Troposphere: Stratosphere: Mesosphere: Thermosphere: T decreases with elevation T increases with elevation T decreases with elevation T increases with elevation 80% of Earth’s gases Most of Earth’s weather happens Most of the measurements Stratosphere: 19.9% of Earth’s gases Ozone layer: Blocking Sun’s ultraviolet radiation

4. Energy from the Sun 1. Characteristics Travels through space (vacuum) in a speed of light 3. Importance to climate and climate change In the form of waves: In stream of particles Electromagnetic waves (Photons) Primary driving force of Earth’s climate engine 2. Electromagnetic spectrum From short wavelength, high energy, gamma rays to long wavelength, low energy, radio waves Releases heat when absorbed Ultraviolet, Visible, Infrared

5. Sun’s Electromagnetic Spectrum Solar radiation has peak intensities in the shorter wavelengths, dominant in the region we know as visible, thus shortwave radiation

6. Blackbody Radiation Curves Any object above absolute zero radiates heat, as proportional to T 4 Any object above absolute zero radiates heat, as proportional to T 4 Higher temperature, shorter wavelength

7. Longwave & Shortwave Radiation The hot sun radiates at shorter wavelengths that carry more energy, and the fraction absorbed by the cooler earth is then re-radiated at longer wavelengths.

8. Atmospheric Greenhouse Effects T= 15°C (59°F) T= –18°C (0°F) Greenhouse effects make Earth’s surface warmer! Surface Temperature With the Atmosphere Surface Temperature Without the Atmosphere

10. Water vapor accounts for 60% of the atmospheric greenhouse effect, CO 2 26%, and the remaining greenhouse gases 14%. Greenhouse Gases Water vapor (H 2 O) Carbon dioxide (CO 2 )Methane (CH 4 ) Nitrous oxide (N 2 O) Ozone (O 3 ) Chlorofluorocarbons (CFC’s) What are they? CO 2 contributes most (55-60%) to the anthropogenic greenhouse effect, and methane is a distant second (16%). CFCs cause the strongest greenhouse warming on a molecule-for-molecule basis.

11. Atmospheric Absorption Solar radiation passes rather freely through Earth's atmosphere. Earth emits longwave energy, which either fits through a narrow window or is absorbed by greenhouse gases and radiated back to Earth. Wavelength Absorption (100%) Nitrous Oxide Methane Ozone Water Vapor Carbon Dioxide Total Atmo IR UV

12. Solar Intensity and Latitude Solar intensity, defined as the energy per area, is different at different latitude. A sunlight beam that strikes at an angle is spread across a greater surface area, and is a less intense heat source than a beam impinging directly.

13. Unequal Radiation on a Sphere Insolation is stronger in the tropics (low latitudes) than in in the polar regions (high latitudes).

14. Pole-to-Equator Heating Imbalances

15. What controls the elevation of the Sun above the horizon? Earth’s Tilt Primarily Determines Season

16. Earth's Annual Energy Balance The balance is achieved locally at only two lines of latitude. A global balance is maintained by excess heat from the equatorial region transferring toward the poles. Incoming Solar Radiation Outgoing Longwave Radiation Unequal heating of tropics and poles

17. The Global Energy Budget: Driver of Atmospheric Motion However, the tilt of the Earth means this balance is not maintained for each latitude A balance exists between the incoming solar and outgoing longwave energy averaged over the globe and the year DEFICIT SURPLUS