1. Climate Earth’s Radiation Balance

2. Solar Radiation Budget Life on earth is supported by energy from the sun Energy from the sun is not simply absorbed by earth, but also retransmitted Without retransmission, all water would boil away & all life would fry The balance between absorption and retransmission of the sun’s energy is called the radiation budget

3. Basic Processes Governing the Radiation Balance

4. Insolation measures the amount of energy coming from the sun via short wave radiation. Measured in watts/sec Top graphic is winter Bottom graphic is summer Insolation

5. Annual Insolation

6. Albedo Degree of reflectivity of the Earth-Atmosphere system (ranges from 0-1) Ice and sand are highly reflective (high albedo) Oceans and forests don’t reflect much (low albedo) top-winter bottom-summer

7. Annual Albedo

8. Short Wave Reflected Radiation Measures the amount of the sun’s energy that is reflected due to the albedo Measured in watts/m 2 Does not affect processes on earth since it is never absorbed Top-winter Bottom-summer

9. Annual Short Wave Reflection

10. Short Wave Absorption The energy absorbed by the earth- atmosphere system Primary cause of earth’s surface temperature

11. Annual Short Wave Absorption

12. Surface Temperature Provides a measure of the temperature all over the Earth Temperatures measured in Kelvin Heat at the surface is translated into long wave radiation

13. Annual Surface Temperature

14. Radiation Spectra for Sun & Earth The wavelength energy emitted by a body is inversely related to the temperature of the body. (nm) = 2.9 x 10 6 /T

15. Outgoing Long Wave Radiation Measures the amount of energy leaving the Earth Results from the surface temperature Also called terrestrial radiation Measured in watts/m 2

16. Annual Long Wave Terrestrial Emission

17. Net Radiation Difference between incoming and outgoing radiation Over time and space this is zero

18. Annual Net Radiation

19. Greenhouse Amount Amount of energy retained by Earth’s atmosphere This storage of energy is called the Greenhouse Effect Necessary for maintaining life on Earth

21. Greenhouse Percent Amount of energy stored in atmosphere Shows Greenhouse Effect as a fraction of the total possible energy that could be stored in the atmosphere Useful for detecting changes over time Annual graphic

23. Partitioning of Incoming SW Radiation ~19 units absorbed in atmosphere to become heat & LW radiation –2 units by ozone –17 units by clouds & gases ~23 units scattered & then absorbed as diffused insolation ~28 units directly absorbed at surface Total absorbed = 70 units

24. Processes of Retransmission Three modes –latent heat (drives hydrological cycle) –sensible heat (atmosphere heated by updrafts) –radiation of IR into space Total of 70 units emitted

25. Comparison of Radiation Budgets of the Terrestrial Planets Compare Earth, Venus & Mars Earth & Venus have similar mass & dimensions; Mars 10% Earth’s mass & half as large Temperatures expected to be in the order: Venus > Earth > Mars Observed: Earth (255 K) > Venus (234 K) > Mars (217 K)

26. The surface temperatures bear little resemblance to their effective temperatures Venus (427 o C) > Earth (15 o C) > Mars (-53 o C) Due to greenhouse effect Venus –extensive atmosphere (100x more mass than Earth’s) –composed mainly of CO 2, H 2 O, SO 2 Mars –atmosphere contains more CO 2 Earth’s –has 100x less water than Earth’s atmosphere