html5-img
1 / 99

GLOBAL ENERGY BUDGET

GLOBAL ENERGY BUDGET. The Greenhouse Effect. Earth’ Surface Temperature. Amount of incident sunlight Reflectivity of planet Greenhouse Effect Absorb outgoing radiation, reradiate back to surface Clouds Feedback loops Atmospheric water vapor Extent of snow and ice cover.

stacy
Télécharger la présentation

GLOBAL ENERGY BUDGET

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. GLOBAL ENERGY BUDGET The Greenhouse Effect

  2. Earth’ Surface Temperature • Amount of incident sunlight • Reflectivity of planet • Greenhouse Effect • Absorb outgoing radiation, reradiate back to surface • Clouds • Feedback loops • Atmospheric water vapor • Extent of snow and ice cover

  3. The “Goldilocks Problem” • Venus – 460 C (860 F) - TOO HOT • Earth – 15 C (59 F) - JUST RIGHT • Mars – -55 C (-67 F) - TOO COLD

  4. The “Goldilocks Problem” • Temperature depends on • Distance from the Sun • AND • Greenhouse effect of its atmosphere • Without Greenhouse effect • Earth’ surface temperature 0 C (32 F)

  5. Global Energy Balance - Overview • How the Greenhouse Effect works • Nature of EMR • Why does the Sun emit visible light? • Why does Earth emit infrared light? • Energy Balance – incoming & outgoing • Calculate magnitude of greenhouse effect • Effect of atmospheric gases & clouds on energy • Why are greenhouse gases greenhouse gases?

  6. Global Energy Balance - Overview • Understand real climate feedback mechanisms • estimate the climate changes that occur • Current • Future

  7. ELECTROMAGNETIC RADIATION • 50% of Sun’s energy in the form of visible light

  8. EMR • Self-propagating electric and magnetic wave • similar to a wave that moves on the surface of a pond • Moves at a fixed speed • 3.00 x 108 m/s

  9. ELECTROMAGNETIC WAVE • 3 characteristics • speed • wavelength • frequency  = c or  = c /  The longer the wavelength, the lower the frequency The shorter the wavelength, the higher the frequency

  10. PHOTONS • EMR behaves as both a wave and a particle • General characteristic of matter • Photon – a single particle or pulse of EMR • Smallest amount of energy able to be transported by an electromagnetic wave of a given frequency • Energy (E) of a photon is proportional to frequency E = h = hc /  where h is Plank’s constant and h =6.626 x 10-34 J-s (joule-seconds)

  11. PLANK’S CONSTANT E = h = hc /  • High-frequency (short-wavelength) photons have high energy • Break molecules apart, cause chemical reactions • Low-frequency (long-wavelength) photons have low energy • Cause molecules to rotate or vibrate more

  12. ELECTROMAGNETIC SPECTRUM

  13. ELECTROMAGNETIC SPECTRUM • Infrared (IR) Radiation • 40% of Sun’s energy • 0.7-1000 m (1 m = 1 x 10-6 m) • Visible Radiation / Visible Light / Visible Spectrum • 50% of Sun’s energy • 400-700 nm (1nm = 1 x 10-9 m) • red longest, violet shortest • Ultraviolet (UV) Radiation • 10% of Sun’s energy • 400-10 nm • X-Rays & Gamma Rays – affect upper atmosphere chemistry

  14. EMR & CLIMATE • Visible & Infrared most important • Why? • Sun? • Earth? • Ultraviolet • Drives atmospheric chemistry • Lethal to most life forms

  15. FLUX • Flux (F) – the amount of energy (or number of photons) in an electromagnetic wave that passes  through a unit surface are per unit time

  16. Flux & Earth’s Climate

  17. The Inverse-Square Law • If we double the distance from the source to the observer, the intensity of the radiation decreases by a factor of (½)2 or ¼

  18. The Inverse-Square Law S = S0 (r0 / r)2 where S = solar flux r = distance from source S0 = flux at some reference distance r0

  19. Solar Flux • The solar flux at Earth’s orbit = 1366 W/m2 • 1AU = 149,600,000 km (average distance from Earth to Sun) • Venus and Mars orbit the Sun at average distances of 0.72 and 1.52 AU, respectively. What is the solar flux at each planet?

  20. The Inverse-Square Law • Small changes in earth’s orbital shape + inverse-square law + solar flux CAN CAUSE LARGE CHANGES IN EARTH’S CLIMATE

  21. TEMPERATURE SCALES • Temperature – a measure of the internal heat energy of a substance • Determined by the average rate of motion of individual molecules in that substance • The faster the molecules move, the higher the temperature

  22. TEMPERATURE SCALES • Celsius - °C • boiling and freezing points of water • Fahrenheit - °F • mixture of snow & salt and human body • Kelvin (absolute) – K • The heat energy of a substance relative to the energy it would have at absolute zero • Absolute zero – molecules at lowest possible energy state

  23. TEMPERATURE SCALES

  24. TEMPERATURE CONVERSIONS T (°C) = [T(°F) – 32] / 1.8 T(°F) = [T (°C) x 1.8] + 32.

  25. TEMPERATURE CONVERSIONS • Convert the following: • 98.6 °F to °C • 20 °C to °F • 90 °C to °F • 100 °F to °C

  26. ABSOLUTE TEMPERATURE T(K) = T (°C) + 273.15 0 K (absolute zero) = -273.15 °C Convert the following: • 98.6 °F to K • 20 °C to K • 90 °C to K • 100 °F to K

  27. BLACKBODY RADIATION • Blackbody – something that emits/absorbs EMR with 100% efficiency at all wavelengths

  28. BLACKBODY RADIATION • Radiation emitted by a blackbody • Characteristic wavelength distribution that depends on the absolute temperature of the body • Plank Function – relates the intensity of the radiation from a blackbody to its wavelength or frequency

  29. BLACKBODY RADIATION CURVE

  30. Blackbody Simulation • Blackbody Simulation

  31. WIEN’S LAW • The flux of radiation emitted by a blackbody reaches its peak value at wavelength λmax, which depends on the body’s absolute temperature • Hotter bodies emit radiation at shorter wavelengths λmax ≈ 2898, where T is temperature in kelvins T λmax is the max radiation flux in μm

  32. WIEN’S LAW

  33. WEIN’S LAW • Sun’s radiation peaks in the visible part of EMR 2898 / 5780 K ≈ 0.5 μm • Earth’s radiation peaks in the infrared range 2898 / 288 K ≈ 10 μm

  34. WEIN’S LAW

  35. ELECTROMAGNETIC SPECTRUM

  36. THE STEFAN-BOLTZMANN LAW • The energy flux emitted by a black body is related to the fourth power of a body’s absolute temperature F = σ T4, where T is the temperature in kelvins and σ is a constant equal to 5.67 x 10-8 W/m2/K4 • The total energy flux per unit are is proportional to the area under the blackbody radiation curve

  37. THE STEFAN-BOLTZMANN LAW

  38. THE STEFAN-BOLTZMANN LAW • Example a hypothetical star with a surface temperature 3x that of the Sun Fsun = σ T4 = (5.67 x 10-8 W/m2/K4) (5780 K)4 = 6.3 x 107 W/m2 Fstar = σ T4 = (5.67 x 10-8 W/m2/K4) (3x5780 K)4 = 34 x σ(5780 K)4 = 81 Fsun

  39. THE NATURE OF EMITTED RADIATION • Wien’s Law – hotter bodies emit radiation at shorter wavelengths • Stefan-Boltzmann – energy flux emitted by a blackbody is proportional the fourth power of the body’s absolute temperature • SO – the color of a star (wavelength) indicates temperature, temperature indicates energy flux

  40. EARTH’S ENERGY BALANCE • The amount of energy emitted by Earth must equal to amount of energy absorbed • The average surface temperature is getting warmer • Imbalance caused by increase in CO2 and other greenhouse gases OR • Imbalance caused by natural fluctuations in the climate system

  41. EARTH’S SURFACE TEMPERATURE • Depends on: • The solar flux (S) available at the distance of Earth’s orbit (30% of incident energy reflected) • Earth’s reflectivity or albedo (A) – the fraction of the total incident sunlight that is reflected from the planet as a whole • The amount of warming provided by the atmosphere (magnitude of the greenhouse effect)

  42. PLANETARY ENERGY BALANCE energy emitted by Earth = energy absorbed by Earth

  43. Effective Radiating Temperature (Te) • The temperature that a true blackbody would need to radiate the same amount of energy that Earth radiates • Use Stefan-Boltzmann law to calculate energy emitted by Earth Energy emitted = σ Te4 x 4  R2

  44. Energy Absorbed by Earth energy absorbed = energy intercepted – energy reflected • Energy Intercepted (Incident Energy)- the product of Earth’s projected area and the solar flux =  R2 S • Energy Reflected - the product of Earth’s incident energy and albedo =  R2 S x A

  45. ENERGY ABSORBED energy absorbed = energy intercepted – energy reflected energy absorbed =  R2 S -  R2 S x A =  R2 S (1 – A)

  46. PLANETARY ENERGY BALANCE energy emitted by Earth = energy absorbed by Earth σ Te4 x 4  R2 =  R2 S (1 – A) σ Te4 = (S/4) (1 – A) where σ is 5.67 x 10-8 W/m2/K4 , T is temperature in kelvin, S is solar flux, and A is albedo The planetary energy balance between outgoing infrared energy and incoming solar energy

  47. MAGNITUDE OF THE GREENHOUSE EFFECT • Effective Radiating Temperature • Atmospheric temperature at which most outgoing infrared radiation derives • Average temperature that Earth’s surface would reach with no atmosphere • Using planetary energy balance equation - • Earth’ s effective radiating temperature = -18C or 0F

  48. MAGNITUDE OF THE GREENHOUSE EFFECT • Actual surface temperature or Earth = 15C • Difference between effective and actual caused by greenhouse effect ∆ Tg = Ts – Te For Earth ∆ Tg = 15C –(–18C) = 33C • By absorbing part of the infrared radiation radiated upward from the surface and reemitting it in both upward and downward directions, the atmosphere allows the surface to be warmer that it would be if no atmosphere were present

  49. THE GOLDLOCKS PROBLEM • A planet’s greenhouse effect is at least as important in determining a planet’s surface temperature as is its distance from the Sun • For homework – Critical Thinking #2

More Related