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The incoming solar energy

The incoming solar energy. Review of last lecture. The standard units of measurements (SI) Earth ’ s three atmospheres: 1st: 4.6 billion years ago , H, He Transition: formation of magnetic field, volcano activities 2nd: 4 billion years ago, CO 2 , H 2 O, N 2

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The incoming solar energy

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  1. The incoming solar energy

  2. Review of last lecture • The standard units of measurements (SI) • Earth’s three atmospheres: 1st: 4.6 billion years ago, H, He Transition: formation of magnetic field, volcano activities 2nd: 4 billion years ago, CO2, H2O, N2 Transition: emergence of life, formation of ocean 3rd: 400 million years ago, O2 Important event: formation of seven continents • What is the residence time? What is the difference between the permanent and variable gases? Name 3 of each. What are the most and second most abundant gases? • Given that variable gases are so rare, why are they considered at all? How are CO2 and O3 changing?

  3. Energy basics • Energy: the ability to do work • Many forms: electrical, mechanical, thermal, chemical, nuclear, … • Joule (J): standard unit of energy (1 J= 0.239 calories) • Watt (W): rate of energy flow (W = 1 J/s)

  4. Methods of Energy Transfer • Conduction • Molecule to molecule transfer • Heat flow: warm to cold • e.g. leather seats in a car • Convection • transferred by vertical movement • physical mixing • e.g. boiling water • Radiation • propagated without medium (i.e. vacuum) • solar radiation provides nearly all energy • The rest of this chapter deals with radiation

  5. Radiation • Everything continually emits radiation • Transfers energy in waves • Waves are both electrical and magnetic, hence electromagnetic radiation • Travels at the speed of light (300,000 km/s). It takes 8 minutes for light from the Sun to reach Earth, and 4.3 years for light from the next nearest star, Proxima Centauri to reach us.

  6. Radiation Quantity and Quality • Quantity: how much?  • Wave height(Intensity). • Quality: what kind?  • Wavelength: distance between crest and crest (or trough and trough). generally reported in μm (microns)- one millionth of a meter.

  7. The Electromagnetic Spectrum The limitations of the human eye!

  8. A man detected by different instruments Infred device Bare eyes X-ray Microscope

  9. Physical Representation of Radiation • Blackbodies: purely hypothetical bodies that absorb and emit the maximum radiation at all wavelengths • The Earth and the sun are close to blackbodies.

  10. What determines the quantity (intensity)?The Stefan-Boltzmann Law • States that the intensity of radiation emitted from a blackbody is a function ONLY of temperature I=T4 where I is the intensity of the radiation, T is the temperature in K, and  is the Stefan-Boltzmann constant, 5.67 x 10-8 W m-2 K-4) • So, hotter bodies emit more energy than colder bodies (double T, 16x more radiation) Earth (290K) I = 401 Wm-2 Sun (6000K) I = 7.3 x 106 Wm-2. So ISun >> Iearth

  11. What determines the quality (wavelength)?The Wein’s Law • States that the peak wavelength of radiation emitted from a blackbody is a function ONLY of temperature max = b/T where max is the peak wavelength of the radiation, T is the temperature in K, and b is the Wein’s displacement constant (2.90 x 10-3 m K) • So, hotter bodies emit at shorter wavelengths Double T, half wavelength Earth (290K) max = 10 μm Sun (6000K)max = 0.5 μm

  12. Wavelength of Sun and Earth Radiation Sun = “shortwave” (0.4-0.7 μm) Peak 0.5 μm (green) Sun Earth = “longwave” (4-100 μm) Peak 10 μm (infrared)

  13. Composition of sunlight

  14. The rainbows

  15. The Sun also emits high energy particles: Northern light (Aurora) • Caused by electrons and protons • They can only penetrate into the atmosphere from the magnetic north pole and south pole • They collide with the atmospheric molecules to generate the aurora

  16. Video: The solar cycle • http://www.youtube.com/watch?v=sASbVkK-p0w&playnext=1&list=PL8EDAE089117E3D77&feature=results_main

  17. The sunspot number - A good index for solar activity • Sunspots are temporary phenomena on the surface of the sun that appear visibly as dark spots • Caused by intense magnetic activity • The number of sunspots changes significantly between solar maximum and solar minimum

  18. The solar cycle • is the periodic change in the sun's activity (including changes in the levels of solar radiation and ejection of solar material) and appearance (visible in changes in the number of sunspots, flares, and other visible manifestations). • has a duration of about 11 years. • has been observed (by changes in the sun's appearance and by changes seen on Earth, such as auroras) for hundreds of years.

  19. The solar cycle and earth’s climate Change of precipitation associated with solar maximum Red-Increase, Blue-decrease (from Meehl et al. 1999, Science)

  20. Solar cycle and US air temperature

  21. Solar cycle and grape production in France

  22. Summary • What is energy? 3 methods of energy transfer • The names of the 6 wavelength categories in the electromagnetic radiation spectrum • Intensity of radiation (Stefan-Boltzman law): I=T4 • Wavelength of radiation (Wein’s law): max = b/T • The wavelength range of Sun (shortwave) and Earth (longwave) radition • The 11-year solar cycle

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