radiation_budget.ppt
- 1. Climate and Global Change Notes 13-1 Earth’s Radiation & Energy Budget Solar-Terrestrial Radiation Relationships Interactions Simple Radiation Budget Shortwave Radiation Interaction with Atmosphere Blue Skies Milky Skies Red Sunsets Shortwave Radiation Budget Science Concepts Reflection and Scattering Absorption Transmission Reflection and Scattering Scattering-Wavelength Relationship Atmospheric Gases Clouds Particulates Absorption Atmospheric Gases Clouds Transmission Atmospheric Gases Clouds The Earth System (Kump, Kastin & Crane) • Chap. 3 (pp. 50-51) • Chap. 4 (pp. 58-59)
- 2. Climate and Global Change Notes 13-2 Earth’s Radiation Budget http://www.cmdl.noaa.gov/ infodata/faq_cat-1.html Science quotes of 5th and 6th graders - Most books now say our sun is a star. But it still knows how to change back into a sun in the daytime. • Simple global radiation budget - Radiation Balance Incident solar radiation - Solar reflected radiation = Earth’s emitted radiation - Otherwise Earth would be warming or cooling What happens to incident solar radiation as it interacts with the Earth’s atmosphere? What are the three things that can happen to radiation when it interacts with an object?
- 3. Climate and Global Change Notes 13-3 Radiation What happens to radiation when it interacts with an object? • Transmission - Energy passes through material basically unchanged, i.e., unchanged energy and wavelength - Note direction may be bent by the process of refraction • Reflection or scattering - Both redirect radiation without changing the energy or wavelength - Scattering redirects radiation in all directions, frequently has more intensity in some directions than other - Reflection redirects radiation in a specific direction • Absorption - Causes molecules to increase their kinetic energy, e.g., increase http://rst.gsfc.nasa.gov/Intro/ Part2_3html.html
- 4. Climate and Global Change Notes 13-4 Solar or Shortwave Radiation Solar Radiation and the Earth’s Atmosphere (Con’t) • Why is the sky blue? • Why is the cloud white?
- 5. Climate and Global Change Notes 13-5 Solar or Shortwave Radiation Solar Radiation and the Earth’s Atmospher e (Con’t) • Why are sunsets and sunrises red?
- 6. Climate and Global Change Notes 13-6 Solar or Shortwave Radiation Solar Radiation and the Earth’s Atmosphere (Con’t) • Why is the Earth white and blue? • Why is the “sky” black? Apollo 11 Earth View • Earthrise viewed from lunar orbit prior to landing http://www.hq.nasa.gov/office/pao/History/ alsj/a11/AS11-44-6551.jpg
- 7. Climate and Global Change Notes 13-7 Solar or Shortwave Radiation Solar Radiation and the Earth’s Atmosphere (Con’t) Answer from 1/31/05 Parade newspaper insert “The light that travels from the Sun to the Earth contains every color there is. But the Earth’s air lets the blue light shine through the best. Sometimes, when the air is very wet after it rains, it makes a rainbow, with all the colors. At sunset, red light can shine through as well.” Do you agree with this answer? 1/31/05 Parade newspaper insert, pp. 17-18.
- 8. Climate and Global Change Notes 13-8 Solar or Shortwave Radiation Scattering by Atmospheric Gases • Scattering redirects energy in all directions • Scattering depends on the size of objects doing scattering compared to the wavelength of incident electromagnetic radiation - For small objects, i.e., atmospheric gas molecules that are about 1000 times smaller than wavelengths of visible light > Intensity of scattering (I), Rayleigh scattering, is inversely related to the wavelength () of the radiation to the fourth power, i.e., I (scattering) 1 / 4 Shorter wavelengths are scattered more than longer wavelengths Note: If the wavelength () of the incident radiation is halved, then the scattered energy will 16 more http://ww2010.atmos.uiuc.edu/(Gh)/ guides/mtr/opt/mch/sct.rxml
- 9. Climate and Global Change Notes 13-9 Solar or Shortwave Radiation Scattering by Atmospheric Gases (Con’t) • Scattering depends on the size of objects doing scattering (Con’t) - For small objects, i.e., atmospheric gases (Con’t) > Examples: (Violet) = 0.425 m, (Blue) = 0.465 m and (Red) = 0.65 m I (Violet) = (Red) 4 = ( 0.65 ) 4 = 4.47 I (Red) (Violet) 4 ( 0.425 ) 4 Violet scatters 4.47 times more than red; Blue scatters 3.76 times more than red > So why isn’t the sky violet? Violet has an even shorter wavelength than blue, thus is scattered even more than blue
- 10. Climate and Global Change Notes 13-10 Solar or Shortwave Radiation Scattering by Atmospheric Gases (Con’t) • Scattering depends on the size of objects doing scattering (Con’t) - For small objects, i.e., atmospheric gases (Con’t) > So why isn’t the sky violet? (Con’t) ‡ Solar radiation has more energy in blue wavelengths than in violet Wehrli, C., 1985: Extraterrestrial Solar Spectrum, Publication no. 615, Physikalisch-Meteorologisches Observatorium + World Radiation Center (PMO/WRC) Davos Dorf, Switzerland.
- 11. Climate and Global Change Notes 13-11 Solar or Shortwave Radiation http://www.croydonastro.org.uk/ Vision7-mod3.pdf Scattering by Atmospheric Gases (Con’t) • Scattering depends on the size of objects doing scattering (Con’t) - For small objects (Con’t) > So why isn’t the sky violet? (Con’t) ‡ Eye has two types of receptors, cones and rods ‡ Cones - color vision, three kinds; yellow-green (564 m), green (534 m) and blue-violet (420 m) (LMS cones) § Typically 64% of cones are yellow-sensitive, ~32% green- sensitive and ~2% blue- sensitive § “Blue” cones are most sensitive § Resulting eye sensitivity for cones and rods - note rapid decrease in sensitivity in violet http://www.darksky.org/VisionSeries/vs2-4.html
- 12. Climate and Global Change Notes 13-12 Solar or Shortwave Radiation http://www.darksky.org/ VisionSeries/vs2-4.html Scattering by Atmospheric Gases (Con’t) • Scattering depends on the size of object doing the scattering (Con’t) - For small objects (Con’t) > So why isn’t the sky violet? (Con’t) ‡ Rods § More cones than rods § More sensitive than cones § Not as color sensitive (only one type) § Function in less intense light than cones, helps with night vision > Experiment - Look at a rose in full moonlight, the flower is brightly lit and may even cast a shadow, but the red is gone, replaced by shades of gray. In fact, the whole landscape is that way. ‡ Why? - Because of low light intensity, you are mainly seeing with the rods which “see” monochromatically, i.e., little color http://science.nasa.gov/headlines/y2006/ 28sep_strangemoonlight.htm?list159742
- 13. Climate and Global Change Notes 13-13 Solar or Shortwave Radiation Scattering by Atmospheric Gases (Con’t) • Apollo 11 Earth View - No scattering of light at the moon’s surface because the moon has no atmosphere, i.e., no gas molecules http://www.hq.nasa.gov/office/pao/History/ alsj/a11/AS11-44-6551.jpg
- 14. Climate and Global Change Notes 13-14 Scattering by Atmospheric Gases (Con’t) > Red sunrises and sunsets Solar or Shortwave Radiation Axis of Rotation Atmospheric Layer Penetration Depth Solar Rays Solar Rays Penetration Depth Sunset
- 15. Climate and Global Change Notes 13-15 Solar or Shortwave Radiation Scattering by Atmospheric Gases (Con’t) • Lunar Eclipse - Note Moon goes from bluish white to reddish as the lunar eclipse proceeds and then back to bluish white - Result of solar radiation of the Earth’s atmosphere scattering blue more than red light http://science.nasa.gov/ headlines/y2000/ ast02feb%5F1.htm
- 16. Climate and Global Change Notes 13-16 > The moon is not always at the same distance from the Earth and its closer proximity causes it to look much larger > We are looking horizontally through a thicker layer of the atmosphere, rather than straight up through a thinner layer and thus the image of the moon is magnified > It is simply an illusion - the image is merely perceived as bigger when the moon is near the horizon How can we test these explanations? Let’s think about how plausible each explanation might be and how we might prove or disprove each one. Solar or Shortwave Radiation An Aside • Why does the Moon appear so large when it is near the horizon? - What are some plausible-sounding explanations?
- 17. Climate and Global Change Notes 13-17 > Facts: Apogee - 405,500 km; Mean - 384,400 km; Perigee - 363,300 km > When the Moon is at apogee, it is 11% farther from Earth, 14% smaller and 30% dimmer than it is at perigee http://spaceweather.com/ 10/23/07 archive Left - A big, bright perigee Moon Right - A lesser apogee Moon Solar or Shortwave Radiation An Aside (Con’t) • The moon is not always at the same distance from the Earth and its closer proximity causes it to look much larger - Does the moon get farther away from the Earth as it rises?
- 18. Climate and Global Change Notes 13-18 Solar or Shortwave Radiation An Aside (Con’t) • It is simply an illusion: the image is merely perceived as bigger when the moon is near the horizon Try the following experiment - Try the following experiment - Look at the moon through a cardboard tube (like those found inside rolls of paper towels). Viewing the moon this way isolates it from the surrounding reference frame of trees and houses. > Stand the cardboard tube on end and trace a circle around the base of the tube onto a piece of paper > Label the circle with the time of your observation > Make your first observation of the moon when it is near the horizon. Look at the moon through the cardboard tube and then make a sketch in the circle you traced showing how much of the tube is filled by the image of the moon > Repeat the above steps every hour or two for about six hours (when the moon is overhead) > Compare your sketches and draw conclusions
- 19. Climate and Global Change Notes 13-19 Solar or Shortwave Radiation An Aside (Con’t) • Optical illusions - Are the yellow lines the same length? http://news.bbc.co.uk/2 /hi/uk_news/magazine/ 4619063.stm
- 20. Climate and Global Change Notes 13-20 Solar or Shortwave Radiation Absorption by Atmospheric Gases • Ozone and oxygen absorbs much of the ultraviolet in the upper atmosphere • Water vapor and carbon dioxide absorb some of the near infrared 100 50 0.3 0.5 1.0 5.0 10.0 20.0 15.0 0 Wavelength (microns) O2, CO2, H2O O3 O3 CO2 H2O H2O CO2, H2O Far Infrared Near IR UV Vis- ible Absorption (%) 95% of Solar Radiation
- 21. Climate and Global Change Notes 13-21 Solar or Shortwave Radiation Absorption by Atmospheric Gases (Con’t) • Atmospheric absorption solar radiation
- 22. Climate and Global Change Notes 13-22 Solar or Shortwave Radiation Absorption by Atmospheric Gases (Con’t) • The atmosphere absorbs, transmits or reflects solar radiation http://en.wikipedia.org/wiki/Image:MODIS_ATM_solar_irradiance.jpg
- 23. Climate and Global Change Notes 13-23 Interaction with Clouds • Clouds, (typical droplets are about 50 times larger than the wavelengths of visible light) when present they reflect, absorb and transmit radiation. - Clouds are very good reflectors of solar radiation. Intensity of reflection related to the cloud depth Cloud depth (m) Albedo (%) 100 75 1000 85 - Clouds are not very good absorbers of solar radiation. Amount of absorption related to the cloud depth Cloud depth (m) Absorption (%) 100 5 1000 10 Solar or Shortwave Radiation Science quotes of 5th and 6th graders - I am not sure how clouds get formed. But the clouds know how to do it, and that is the important thing.
- 24. Climate and Global Change Notes 13-24 Solar or Shortwave Radiation Interaction with Particulates • Atmospheric particulates scatter radiation - For larger objects (dust, pollution and droplets) intensity of scattering is equal for all wavelengths, called Mie scattering. Causes haze, milky color sky. Increases albedo. • Example - Great Smoky Mountains Clear Day Hazy Day http://www.epa.gov/oar/vissibility/what.html Particles such as sulfates, scatter more light, particularly during humid conditions. Natural sources of haze-causing pollutants include dust, and soot from wildfires. Manmade sources include vehicles, electric utility and industrial fuel burning, and manufacturing. Some haze-causing particles are formed from gases emitted many miles upwind.
- 25. Climate and Global Change Notes 13-25 Solar or Shortwave Radiation What do we mean when we say “Once in a blue moon…”? • According to modern folklore, a Blue Moon is the second full moon in a calendar month. Usually months have only one full moon, but occasionally a second one sneaks in. - Full moons are separated by 29 days, while most months are 30 or 31 days long; so it is possible to fit two full moons in a single month - This happens every two and a half years, on average. > For example: July 2004 had one full moon on 2 July and another on 31 July which was by definition a Blue Moon • Truly “blue” colored Moon’s can be cause by atmospheric particulates about 1 micron (near the size of red light scatter red light, while allowing other colors to pass) in size, for example, volcanic ash or forest fires - Blue Moon’s occurred in 1883 and for years after when Krakato erupted - Other examples include > El Chichon (1983) in Mexico > Mt. St. Helens (1980) in U.S. > Mount Pinatubo (1991) in Philippines http://science.nasa.gov/headlines/ y2004/07jul_bluemoon.htm?list104690
- 26. Climate and Global Change Notes 13-26 Solar or Shortwave Radiation Summary of Interaction with the Earth’s Atmosphere • Most (55%) visible radiation or energy reaches the Earth’s surface. Incoming Solar Radiation 100% Total Albedo 30% 3% Absorbed by Clouds 16% Absorbed by Air 4% Reflected from Surface 20% Reflected by Clouds 6% Scattered by Air 25% Direct 26% Diffuse 51% Absorbed at the Earth's Surface Air here refers to the gas molecules and particulates
- 27. Climate and Global Change Notes 13-27 Solar or Shortwave Radiation Surface Albedo • Uses MODIS data composited over a 16-day period, from April 7-22, 2002 • White indicates no data and no albedo data are provided over oceans http://earthobservatory.nasa.gov/Newsroom/ NasaNews/2002/200207099816.html Note: This is surface albedo Where are the regions with the highest albedo? What type of surfaces do these regions have?
- 28. Climate and Global Change Notes 13-28 Solar or Shortwave Radiation Reflected Solar Radiation Reflected Solar Radiation (W/m2) Winter solstice, 22 December 2004 Summer solstice, 20 June 2005 http://earthobservatory.nasa.gov/Newsroom/ NewImages/images.php3?img_id=17130 Note: These images are top-of-atmosphere reflected energy as seen by satellite, not surface only reflected energy What dominates the albedo in these images?
- 29. Climate and Global Change Notes 13-29 Earth’s Radiation & Energy Budget Shortwave Radiation Interaction with Earth’s Surface Surface Types Soil Moisture and Vegetative Effects Albedo Water Water and Land Differences Science Concepts Reflection and Scattering Absorption Energy Versus Temperature Specific Heat Absorption Specific Heat Mixing Evaporation
- 30. Climate and Global Change Notes 13-30 Solar Radiation at the Earth Surface What happens to solar radiation as it interacts with the Earth’s surface? • Absorbed or reflected - Examples: Albedo or Material Absorption Reflection Fresh Snow 25-5% 75-95% Old Snow 60-30% 40-70% Sea Ice 70-60% 30-40% Desert 75-70% 25-30% Glacier Ice 80-60% 20-40% Grass 84-74% 16-26% Crops 85-75% 15-25% Deciduous Forest 85-80% 15-20% Tundra 85-80% 15-20% Soil 85% 15% Water (Low Sun) 90-0% 10-100%* Asphalt 94% 6% Coniferous Forest 95-85% 5-15% Water (High Sun) 97-90% 3-10%* *albedo of water depends on the solar angle and sea surface roughness
- 31. Climate and Global Change Notes 13-31 Solar Radiation at the Earth Surface Interaction with the Earth’s Surface • What is wrong with this statement? “Albedo was technically defined as the ratio of electromagnetic energy reflected by a surface to the amount of energy incident upon it. In terms of the visible spectrum. it was a measure of how ‘shiny’ a surface was. A river had a high albedo, since water reflected most of the sunlight striking it. Vegetation absorbed light, and therefore had a low albedo.” “Congo” by Michael Crichton, p. 69. http://www.ucar.edu/communications/ CCSM/overview.html
- 32. Climate and Global Change Notes 13-32 Solar Radiation at the Earth Surface Specific Heat Capacity • Specific heat (heat capacity) is the amount of heat per unit mass required to raise the temperature by one degree Kelvin or Celsius - Coefficient which is related to how efficiently a material converts energy into sensible temperature change ( Temperature change of object ) = ( Energy absorbed or given up by object ) ( Object’s specific heat * Mass of object ) Specific Heat Capacity Specific Heat Capacity Substance cal / (g K) Substance cal / (g K) Water 1.00 Ice (@ 0°C) 0.48 Asphalt 0.22 Brick 0.20 Aluminum 0.22 Concrete 0.21 Copper 0.09 Glass (Typical) 0.20 Gold 0.03 Granite 0.19 Iron 0.11 Sand 0.20 Soil (Dry) 0.19 Soil (Typical) 0.25 Soil (Wet) 0.35 Wood (Typical) 0.40 Dry air (@ sea-level pressure) 0.24 Saturated air (@ sea-level pressure) 0.25
- 33. Climate and Global Change Notes 13-33 Solar Radiation at the Earth Surface Interaction with the Earth’s Surface (Con’t) • Example: Given one gram of material, what will be the temperature change if one calorie of electromagnetic energy impinges on the material? - Water - 90% absorbed, thus 0.9 cal of heat available to warm the water Change in temperature = Energy / ( Mass * Specific Heat ) = 0.9 cal / ( 1 g * 1 cal / g -°C ) = 0.9°C - Soil - 85% absorbed, 0.85 cal of heat available to warm the soil Change in temperature wet or dry = 0.85 cal / ( 1 g * 0.35 or 0.19 cal / g -°C ) = 2.43 or 4.47°C - Asphalt - 94% absorbed, 0.94 cal of heat available to warm the asphalt Change in temperature = 0.94 cal / ( 1 g * 0.22 cal / g -°C ) = 4.27°C
- 34. Climate and Global Change Notes 13-34 Solar Radiation at the Earth Surface Interaction with the Earth’s Surface (Con’t) • Why does land becomes hotter than water during the day? - Water absorbs energy in a deeper layer, i.e., more mass because it is more transparent - Water has higher specific heat - Water is a fluid and can mix the energy throughout a deeper layer - More of the energy is used to evaporate water over water surfaces than over land surfaces • Daily temperature range Soil Deep Circulating Pool Pool 16" Deep 10 20 30 40 50 4 8 12 16 Temperature Range (°F) Inches
- 35. Climate and Global Change Notes 13-35 Earth’s Radiation & Energy Budget Surface Budget Surface Energy Budget Fluxes Bowen Ratio Science Concepts Conduction Convection Sensible Heat Latent Heat Radiation
- 36. Climate and Global Change Notes 13-36 Earth’s Surface Energy Budget What happens to the energy absorbed at the Earth’s surface? • Conduction - Into ground • Convection - Important cause of weather - About 20% of energy transfer - Two types > Sensible (Temperature change) - about 25% > Latent (Evaporation) - about 75% > The Bowen Ratio (BR) is the ratio of the sensible heating to latent heating Bowen Ratio = Sensible Heating Latent Heating Thus, the Earth’s average BR = 25% / 75% = 0.33
- 37. Climate and Global Change Notes 13-37 Earth’s Surface Energy Budget Energy Absorbed at the Earth’s Surface (Con’t) • Convection (Con’t) - Two types (Con’t) > The Bowen Ratio (BR) varies depending on the surface type and meteorological conditions Geographical Area Bowen Ratio Europe 0.62 Asia 1.14 North America 0.74 South America 0.56 Africa 1.61 Australia 2.18 Atlantic Ocean 0.11 Indian Ocean 0.09 Pacific Ocean 0.10 All land 0.96 All oceans 0.11 Note: Dry areas like Australia have high BR while wet areas like oceans have low BRs, i.e., over dry areas, more energy is transferred from the surface to the atmosphere via sensible heating while over wet areas, more energy is transferred to the atmosphere via evaporation of water
- 38. Climate and Global Change Notes 13-38 Earth’s Surface Energy Budget Energy Absorbed at the Earth’s Surface (Con’t) • Convection (Con’t) - Two types (Con’t) > Examples: 1. Congo rain forest maximum surface temperatures about 30°C cooler than adjacent semiarid lands 2. Dense irrigated poplar tree farm (red) next to arid natural vegetation in northeastern Oregon http://www.agu.org/journals/eo/eo0643/ 2006EO430002.pdf Eos, Vol. 87, No. 43, 24 October 2006
- 39. Climate and Global Change Notes 13-39 Earth’s Surface Energy Budget Energy Absorbed at the Earth’s Surface (Con’t) • Convection (Con’t) - Two types (Con’t) > BR varies depending on soil moisture availability > Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images on 8/27/06 ‡ Top vegetation index, a measure of plant density § Dense vegetation is dark green § Sparse vegetation is pale green ‡ Bottom is surface temperature ‡ Note contrast between irrigated and non-irrigated land, irrigated crop lands are much cooler, 30°C (54°F) cooler, than surrounding native vegetation http://earthobservatory.nasa.gov/Newsroom/ NewImages/images.php3?img_id=17486
- 40. Climate and Global Change Notes 13-40 Earth’s Surface Energy Budget Energy Absorbed at the Earth’s Surface (Con’t) • Convection (Con’t) > The Bowen Ratio (BR) Effect of soil moisture on maximum temperatures Eta model volumetric soil water content (0-10 cm) over Northern Alabama and daily maximum temperature at Huntsville, AL
- 41. Climate and Global Change Notes 13-41 Earth’s Surface Energy Budget Energy Absorbed at the Earth’s Surface (Con’t) • Radiation - Infrared (IR) or “Longwave” wavelengths - Accounts for about 80% of energy transfer
- 42. Climate and Global Change Notes 13-42 Earth’s Radiation & Energy Budget Longwave Radiation’s Interaction with Atmosphere Greenhouse Gases Longwave Radiation Budget Science Concepts Reflection and Scattering Atmospheric Gases Clouds Absorption Atmospheric Gases Clouds Transmission Atmospheric Gases Clouds
- 43. Climate and Global Change Notes 13-43 Earth or Longwave Radiation What happens to “longwave” radiation emitted by Earth’s surface? • Absorbed, transmitted or reflected by the atmosphere - 5% transmitted - 95% absorbed • Absorbed by “Greenhouse” gases - Water Vapor Absorption (%) 0.1 0.3 0.5 0.7 1 5 10 15 20 0 50 100 Wavelength (micrometers) Water Vapor 95% of Earth’s Radiation
- 44. Climate and Global Change Notes 13-44 0.1 0.30.50.7 1 5 10 15 20 0 50 100 Carbon Dioxide 0.1 0.30.50.7 1 5 10 15 20 0 50 100 Molecular Oxygen and Ozone Earth or Longwave Radiation Interaction with Earth’s Atmosphere (Con’t) Absorption (%) 0.1 0.30.50.7 1 5 10 15 20 0 50 100 Wavelength (micrometers) Methane Absorption (%) 0.1 0.30.50.7 1 5 10 15 20 Wavelength (micrometers) 0 50 100 Nitrous Oxide
- 45. Climate and Global Change Notes 13-45 Earth or Longwave Radiation Interaction with Earth’s Atmosphere (Con’t) • Absorbed by “Greenhouse” gases (Summary) - “Atmospheric Window” > 8-11 microns 100 50 0.3 0.5 1.0 5.0 10.0 20.0 15.0 0 Wavelength (microns) O2, CO2, H2O O3 O3 CO2 H2O H2O CO2, H2O Far Infrared Near IR UV Vis- ible Absorption (%) 95% of Earth’s Radiation
- 46. Climate and Global Change Notes 13-46 Earth or Longwave Radiation Interaction with Earth’s Atmosphere (Con’t) • Clear atmosphere absorbs Earth’s radiation Interaction with Clouds • Liquid water (cloud droplets) absorbs almost all IR (Infrared or longwave radiation) • Emit IR in all directions depending on its temperature
- 47. Climate and Global Change Notes 13-47 Clouds and Radiation Budget Effects of Clouds • Reflect solar radiation • Absorb longwave radiation Net Effects of Clouds • Deep, convective clouds - Have tops that are highly reflective (high albedo) to solar shortwave radiation - cooling effect > However, because their tops are high, and thus cold, they emit little longwave from their tops - Bases readily absorb Earth’s longwave radiation - warming effect - Net result is that deep, convective clouds have a neutral (neither warming or cooling) effect on Earth’s climate system
- 48. Climate and Global Change Notes 13-48 Clouds and Radiation Budget Net Effects of Clouds (Con’t) • Clouds (Con’t) - High, thin cirrus clouds > Mostly transparent (low albedo) to solar radiation > Readily absorb Earth’s longwave radiation and emit longwave in all directions, some up and some down > Net result is they warm Earth’s climate system - Low, thicker altostratus or stratus clouds > Highly reflective (high albedo) to solar shortwave radiation > Readily absorb Earth’s longwave radiation and emit longwave in all directions, some up and some down > Net result is that they cool the Earth’s climate system Solar transmitted Solar transmitted Surface emitted IR Surface emitted IR Cloud emitted IR Cloud emitted IR Low Cloud High Cloud Cloud reflected solar Cloud reflected solar Cloud emitted IR Cloud emitted IR
- 49. Climate and Global Change Notes 13-49 Clouds and Radiation Budget Net Effects of Clouds (Con’t) • Condensation trails (Contrails) - If air through which the airplane is flying is nearly saturated, contrail will form easier and last longer than if the air is dry - Lingering contrails can spread out into a cirrus layer of cirrus - This MODIS image on 11/25/06 contains scores of contrails over the Midwest, - Mingled contrails have created a thick cloud over the top part of the scene (not all the clouds in the region are necessarily contrails) - To the south, more distinct individual tracks are visible http://earthobservatory.nasa.gov/Newsroom/ NewImages/images.php3?img_id=17474
- 50. Climate and Global Change Notes 13-50 Clouds and Radiation Budget Net Effects of Clouds (Con’t) • Condensation trails (Contrails) - Contrails can influence the climate by increasing the cloud cover in heavy air-traffic regions - Recall thin cirrus clouds cause warming; their thinness makes them not very good solar radiation absorbers, but they do absorb outgoing radiation - NASA scientists have discovered that contrail-generated cirrus clouds could be responsible for much of the warming of surface temperatures over the U.S. from 1975-1994 http://earthobservatory.nasa.gov/Newsroom/ NewImages/images.php3?img_id=17474
- 51. Climate and Global Change Notes 13-51 Clouds and Radiation Budget Net Effects of Clouds (Con’t) • Reducing Night Flights May Ease Winter Global Warming, Report Says Clouds of ice formed in the trails of jet exhaust trap heat and prevent the earth from cooling. From the Los Angeles Times By Robert Lee Hotz, June 15, 2006 Contrails from winter night flights may be most responsible for the global warming caused by air traffic, even though they constitute a fraction of commercial flights, meteorologists at the University of Reading reported Wednesday. Though there would be enormous practical problems, airlines could markedly reduce aviation's impact on climate by changing schedules to restrict night flying, the researchers said in the journal Nature. "We get one-half of the climate effect from one-quarter of the year, from less than one-quarter of the air traffic," said meteorologist Nicola Stuber, who led the English research team. "If you get rid of the night flights, you can reduce the climate warming effect of the contrails." Overall, aviation accounts for a relatively small portion of the emissions involved in rising global temperatures, but international commercial air travel is among the fastest growing unregulated sources of greenhouse gases and a topic of concern among climate regulators. http://www.latimes.com/news/printedition/asection/ la-sci-nightfly15jun15,1,3604880.story?coll=la-news-a_section
- 52. Climate and Global Change Notes 13-52 Clouds and Radiation Budget Net Effects of Clouds (Con’t) • Reducing Night Flights May Ease Winter Global Warming, Report Says (Con’t) By its accounting, the International Air Transport Assn. says that air traffic accounts for just 2% of global carbon dioxide emissions. Jet exhaust, however, injected at high altitude can have two or three times the warming effect of carbon dioxide alone, researchers have concluded. In particular, climate experts have worried about the impact of the trails of ice particles that quickly condense in the wake of jet exhaust, which can spread in hours from a few yards wide to thousands of square miles. These shining clouds are mirrors in the sky. From their upper surface, they reflect solar radiation, causing a slight cooling. At the same time, they block any heat rising from the earth below, enhancing the greenhouse effect. At night, that warming is especially pronounced, the researchers determined. To explore the climate effects of contrails, Stuber and her colleagues studied the airspace over the south of England at the entrance to the North Atlantic flight corridor, perhaps the world's busiest skyway, with as many as 36,000 flights per month.They looked only at information on contrails that persisted for an hour or more, combining aircraft flight data with weather balloon recordings of temperature and humidity. Contrails were almost twice as likely to form in winter as in summer. http://www.latimes.com/news/printedition/asection/ la-sci-nightfly15jun15,1,3604880.story?coll=la-news-a_section
- 53. Climate and Global Change Notes 13-53 Clouds and Radiation Budget Net Effects of Clouds (Con’t) • Reducing Night Flights May Ease Winter Global Warming, Report Says (Con’t) Stuber determined that night flights accounted for 25% of the daily air traffic but contributed 60% to 80% of the climate effect. Moreover, winter flights accounted for 22% of the annual total but contributed half of the annual warming. "If we control emissions from other sources and don't do something about aircraft, then in the future they are going to become a dominant source," said atmosphere expert Joyce E. Penner at the University of Michigan. "Maybe there are ways to avoid such a high climate impact by scheduling different routings." http://www.latimes.com/news/printedition/asection/ la-sci-nightfly15jun15,1,3604880.story?coll=la-news-a_section
- 54. Climate and Global Change Notes 13-54 Clouds and Radiation Budget Net Effects of Clouds (Con’t) • Clouds (Con’t) - Clouds containing many aerosols (left) also contain many tiny water droplets - Such clouds reflect light (solar radiation) well - Clouds containing fewer aerosols (right) tend to contain fewer and larger water droplets - they transmit more solar energy to the Earth’s surface http://science.nasa.gov/headlines/y2002/ 22apr_ceres.htm?list104690
- 55. Climate and Global Change Notes 13-55 Earth Energy Budget http://www.globalchange.umich.edu/globalchange1/ current/lectures/samson/global_warming_potential/ http://asd-www.larc.nasa.gov/ceres/ brochure/clouds_and_energy.html Budgets • Percentage • W / m2
- 56. Climate and Global Change Notes 13-56 Earth Energy Budget http://asd-www.larc.nasa.gov/erbe/components2.gif Budgets • Percentage
- 57. Climate and Global Change Notes 13-57 Earth Energy Budget Budgets • Percentage & W / m2 • Note numbers do not exactly match, but this depiction shows the greenhouse effect http://www.ngdc.noaa.gov/paleo/ctl/about4.html
- 58. Climate and Global Change Notes 13-58 Earth Energy Budget Budgets Surface (Watts m-2) Atmos. Solar Earth Sensible Latent Solar Top of Atmos. Source Rad. Rad. Heat Heat Absorb Albedo National Acad. of Sciences (1975) 174 72 24 79 65 30 Paltridge & Platt (1976) 174 68 27 79 65 30 Budyko (1982) 157 52 17 88 81 30 MacCracken (1985) 157 51 24 82 79 31 Henderson-Sellers & 171 68 24 79 68 30 Robinson (1986) Ramanathan (1987) 169 63 16 90 68 31 Schneiderf 154 55 17 82 86 30 Liou (1992) 151 51 21 79 89 30 Peixoto & Oort (1992) 171 68 21 82 68 30 Hartmann (1994) 171 72 17 82 68 30 Rossow & Zhang (1995) 165 46 66 33 Kiehl & Trenberth (1997) 168 66 24 78 67 31 Top of Atmosphere Incoming Solar radiation = 342 Watts m-2 Kiehl, J.T., and K.E. Trenberth, 1997: Earth’s annual global mean energy budget. Bull. Amer. Meteor. Soc., 78, 197-208.