Fire and Smoke

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Fire and Smoke. How does fire affect climate? Forest fires, brush fires, and slash and burn agriculture are a significant force for environmental change, both locally and globally. Intentional deforestation by burning radically alters local landscapes.
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Fire and SmokeHow does fire affect climate?Forest fires, brush fires, and slash and burn agriculture are a significant force for environmental change, both locally and globally. Intentional deforestation by burning radically alters local landscapes. At regional scales, fires naturally shape ecosystems such as the boreal forest (Canada, Alaska and Russia) and chaparral (Southern California). Globally, fires may play an important role in climate change, emitting both greenhouse gases and smoke particles (aerosols) into the atmosphere. These emissions almost certainly played a role in the 0.5°C increase in the Earth's average surface temperature over the past 100 years.http://earthobservatory.nasa.gov/Library/Deforestation/deforestation_update2.htmlhttp://earthobservatory.nasa.gov/Study/BOREASFire/http://earthobservatory.nasa.gov/Library/GlobalFire/Fire changes local & micro- scalesurface energy budgetSmoke affectsradiation budgetFire & SmokeClimate EffectsFire changes green-house gas budgetSmoke changescloud physicsSmoke changescloud initiationand life cycleFire and SmokeWhat changes occur when a forest or grassland fire happens?CrestAmplitudeHeightTroughWavelengthRadiation PrimerWhat is radiation?Radiation can be particles (protons, electrons, etc.) or electromagnetic waves (x-rays, ultraviolet light, visible light, etc.)For this discussion, we will limit ourselves to electromagnetic radiation - Electromagnetic radiation can transfer energy without requiring a medium, i.e., through a vacuum > Other mechanisms that transfer energy, such as conduction and convection, do not work without a medium - All objects with temperature above absolute zero emit electromagnetic radiation - Analogy of waves is often used to describe electromagnetic radiationFrequency (hertz)Wavelength(m)23-141010GammaRays-10101810X Rays-610Ultraviolet1410VisibleInfrared-210Microwaves10101TV210 TV - FMShort-wave610Broadcast Band610Long - WaveRadio2101Radiation PrimerWhat is the range of electromagnetic radiation wavelengths emitted by objects?Note: micron= m = 10-6 m Note: Visible wavelengths range from 0.4 to 0.7 micronsExam Scores2018161412Number of Students per Grade Interval10864200102030405060708090100GradesRadiation PrimerWhat is the range of radiation wavelengths emitted by objects?All objects with a temperature above absolutezero emit electromagnetic radiationRadiation from solid and liquid materials is emitted with a range of wavelengths similar to a histogram of scores on an examFor radiation, this spread of energy per wavelength versus wavelength is called a spectrumTemperature is a measure of the average kinetic energy (energy related to motion) of the atoms and molecules in a substanceThe Absolute or Kelvin temperature scales (based on the study of gases and thermo-dynamics) have a more physical meaning of zero than the Centigrade or Fahrenheit scalesAn object at 0 K has a minimum of kinetic energy, not zero kinetic energyVisible17,500max15,00012,500Emitted Radiation Per Wavelength Interval(Cal - cm-2 - min - mm -1 )10,0007,5005,0002,50000.00.51.01.52.0Wavelength (m)mRadiation PrimerWhat wavelengths does the Sun emit?Below is the Sun’s emitted radiation spectrum; assumes the Sun’s outer surface temperature is 6000 KNote: 1 calorie = energy required to heat 1 gm of water 1°C Note: 1 Calorie (capital C; Unit used for food derived energy) = 1000 calories (lower case c) = 1 kilocalorieNote: The Sun emits much of it’s radiation in the visible range with its wavelength of maximum emission, (max), is about 0.48 m, i.e., in the blue-green range95% of the Sun’s emitted radiation is in the region between 0.25 and 2.5 mRadiation PrimerWhat wavelengths does the Earth emit?Below is the Earth’s emitted radiation spectrum; assumes the Earth’s surface temperature is 288 KNote: Energy amounts per wavelength interval much smaller than for the Sun Note: The Earth’s wavelength of maximum emission, (max), is about 9.8 m max0.05095% of the Earth’s emitted radiation (gray area) is in the region between 2.5 and 25 m, i.e., at much longer wavelengthsEmitted RadiationPer Wavelength Interval(Cal - cm-2 - min - mm -1 )0.02503020010Wavelength (m)mRadiation PrimerWhat 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 refractionReflection or scattering - Both redirectradiation without changing the energy or wavelength - Scattering redirects radiation in all directions, frequently has more intensity in some directions than in others - Reflection redirects radiation in a specific direction; like pool balls collidingAbsorption - Causes molecules to increase their kinetic energy, e.g., increase their temperaturehttp://rst.gsfc.nasa.gov/Intro/Part2_3html.htmlRadiation PrimerWhat happens to solar radiation when it encounters the Earth’s atmosphere?It is - absorbed by atmospheric gases, - scattered from atmospheric gases, - transmitted through atmospheric gases to the Earth’s surface, - absorbed by clouds, - reflected by clouds, - transmitted through clouds to the Earth’s surface, - scattered by aerosols, - absorbed by aerosols, - transmitted through aerosols to the Earth’s surface, - reflected by the Earth’s surface, - absorbed by the Earth’s surface.Radiation PrimerHow does atmospheric composition affect these processes?Most gases and aerosols (particulates - dust, salt particles, smoke, pollen, air pollution, products from volcanic eruptions, etc.) scatter solar radiation and thus, tend to increase the atmosphere’s albedo, i.e., cause the atmosphere to reflect more solar energy back to space, thus reducing the energy reaching the Earth’s surface - Particles the size of atmospheric gas molecules (much smaller than the wavelengths of the center of the solar radiation spectrum) scatter shorter wavelengths much more than longer wavelengths; reason for blue skies and red sunsets - Particles larger than the wavelengths of solar radiation scatter all visible wavelengths equally; reason for haze and skies that are milky and less bluehttp://eospso.gsfc.nasa.gov/ftp_docs/NASA-Facts-Aerosols.pdfRadiation PrimerHow does atmospheric composition affect these processes? (Con’t)Example - Great Smoky Mountains Clear Day Hazy Day http://www.epa.gov/oar/vissibility/what.htmlParticles such as sulfates and salt particles (left by evaporating sea spray) grow during humid conditions, becoming larger than the wavelengths of visible radiation. Natural sources of haze-causing pollutants include dust, and smoke fromwildfires. Manmade sources include vehicles, electric utility and industrial fuel burning, and manufacturing. Some haze-causing particles are formed from gases and particulates emitted many miles upwind. Radiation PrimerAside: How do clouds affect these processes?Clouds (typical droplets are about 50 times larger than the wavelengths of visible light) reflect, absorb and transmit radiation - Clouds are very good reflectors of solar radiation. Percentage of solar energy reflected 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 depthCloud depth (m)Absorption (%) 100 5 1000 10Incoming SolarRadiation 100% Total Albedo 30%6% Scatteredby Air4% Reflectedfrom Surface20% Reflectedby Clouds25% Direct3% Absorbedby Clouds16% Absorbedby Air 26% Diffuse51% Absorbed at theEarth's SurfaceRadiation PrimerWhat happens to solar radiation when it encounters the Earth’s atmosphere? Global solar radiation budget Most (55%) visible radiation reaches the Earth’s surfaceAir here refers to the gas molecules and particulatesEarth Surface Energy PrimerWhat happens to solar radiation that reaches Earth’s surface?Absorbed or reflected - Examples: Albedo or MaterialAbsorptionReflection 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 (daily average given). Low angle more albedo.Earth Surface Energy PrimerWhat happens to solar radiation that reaches Earth’s surface? (Con’t)Composited Surface Albedo - MODIS 16-day composited surface albedo, from April 7-22, 2002 • White indicates no data and no albedo data are provided over oceansNote: This is surface albedoWhere are the regions with the highest albedo?What type of surfaces do these regions have? http://earthobservatory.nasa.gov/Newsroom/NasaNews/2002/200207099816.htmlEarth Surface Energy PrimerWhat happens to solar radiation that reaches Earth’s surface?(Con’t)Reflected Solar Radiation (W/m2) Winter solstice, 22 December 2004 Summer solstice, 20 June 2005Note: These images are top-of-atmosphere reflected energy as seen by satellite, not surface only reflected energyWhat dominates the albedo in these images?http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17130Earth Surface Energy PrimerHow does the Earth’s surface cool?Conduction - Into ground - Averages to zero over a year; into ground spring/summer, out of ground fall/winterConvection - Important cause of weather - About 20% of the energy leaves the Earth’s surface by two types of convection < Latent heat (Evaporation) - about 75% of the 20% < Sensible heat (Temperature change) - about 25% of the 20% § Definition - Bowen Ratio (BR) is the ratio of the sensible heating to latent heating, i.e., Bowen Ratio = Sensible Heating Latent Heating - From above, the Earth’s average BR = 25% / 75% = 0.33Radiation - Remaining 80% of the energy leaves the Earth’s surface by “longwave” radiationEarth Surface Energy PrimerHow does the Earth’s surface cool? (Con’t)The Bowen Ratio (BR) varies depending on the surface type and meteorological conditions Geographical AreaBowen 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 0.11Note: 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 waterEarth Surface Energy PrimerHow does the Earth’s surface cool? (Con’t)Example: Dense irrigated poplar tree farm (red) next to arid natural vegetation in northeastern OregonNote: In the watered, treed area has a surface temperature of 33°C (low Bowen ratio) while the dry natural areas (high Bowen ratio) have surface temperatures of 59.8°C and 60.4°C60.4°C33°C59.8°CEos, Vol. 87, No. 43, 24 October 2006Earth Surface Energy PrimerHow does the Earth’s surface cool? (Con’t)Example: 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 temperatureNote contrast between irrigated (low Bowen ratio) And non-irrigated (high Bowen ratio) land, irrigated crop lands are much cooler, 30°C (54°F) cooler, than surrounding native vegetationhttp://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=1748616°C48°CShort- or long- termeffects?Forest or grassland?Effect on albedo?Vegetated vs BurnedEffects on greenhouse gases?Effect on Bowen ratio? Tropical, midlatitude orboreal region?Fire and SmokeWhat are the local climate effects of a fire?What changes in surface characteristics occur when a fire happens? - Changes from a living, green, vegetated to a lifeless, blackened surfaceAlbedo is the amount of electromagnetic energy reflected divided by the amount of incident energy Bowen ratio is the ratio of the sensible heating to latent heatingFire and SmokeHow does a change from a green vegetated surface to a black charred surface change the local radiation balance?Spectral response depends on surfaceLeaves reflect green and near IR; absorbs other wavelengthsNote: Average reflectance of bare soil over the range of 95% of the emitted solar energy is higher than that of a vegetated surfaceThus, it might be expected that the albedo-effect of the burned surface would be to cool the surface temperature in the burned area95% of solar energyFire and SmokeHow does smoke affect the balance of greenhouse gases?(Con’t)20%0%Govaerts, Y.M.; B. Pinty, A. Lattanzio, 2003: Impact of vegetation fires on surface albedo dynamics and absorbed solar radiation over the African Continent, Geoscience and Remote Sensing Symposium, 2003. IGARSS apos;03. Proceedings. 2003 IEEE International. Volume 3, Issue, 21-25 July 2003 Page(s): 1576 - 1578. (http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/9010/28603/01294180.pdf}200Note: Lower albedo, more solar energy absorbed at surface - thus warmerBecause burned surface is black?Fire and SmokeHow does a change from a living surface to lifeless surface change the local radiation balance? (Con’t)Example: Results from MODIS albedo data from the years 2000 through 2004 from interior AlaskaFirst decade after fire, spring albedo (March and April) increased by 0.165 as compared with unburned areas that served as a control. Summer albedo (June and July) shows an initial decrease of 0.023, which recovers in five years, followed by an increase of 0.025. Spring albedo reaches its maximum at nine years since fire while the summer albedo maximum is at 20 years. Both spring and summer albedos recover to pre-fire levels in 49 to 51 years. When converted to radiative forcing, these sustained increases in both summer and winter albedo could offset the heating from greenhouse gasses released during the fire.Post-fire changes in surface albedo associated with vegetation succession in boreal forest ecosystems. A.E. Lyons, Y. Jin, and J.T. Randerson, University of California, Irvine. (http://adsabs.harvard.edu/abs/2005AGUFM.B33E1096)Fire and SmokeHow does a change from a living surface to lifeless surface change the local radiation balance? Example: In boreal region post-fire ecosystem affects the albedo in several ways • Loss of the canopy overstory leads to greater snow cover and higher surface albedos during spring • Grasses and deciduous trees that tend to establish in early and intermediate stages of succession have a more reflective canopy than mature black spruce ecosystemsBoreal Region - “The northern boreal ecoregion accounts for about one third of this planet's total forest area. It is comprised of a broad circumpolar band which runs through most of Canada, Russia, Scandinavia and parts of Northern Scotland.”http://www.sierraclub.org/ecoregions/boreal.aspPost-fire changes in surface albedo associated with vegetation succession in boreal forest ecosystems. A.E. Lyons, Y. Jin, and J.T. Randerson, University of California, Irvine. (http://adsabs.harvard.edu/abs/2005AGUFM.B33E1096)Fire and SmokeHow does a change from a living surface to lifeless surface change the local radiation balance?Example: Study focused on physical changes to an Australian savanna landscape caused by fire and the resultant effects of fire scars on boundary layer heating • Albedo values were found to almost halve after fire ranging from 0.12 pre-burn to 0.07 post-burn • Fundamental change in energy partitioning, with a reduction in evapotranspiration and an increase in sensible heating to the atmosphere - Evident in recorded Bowen ratio (sensible/latent heat flux ratio) for the pre-burn landscape of 2.5 compared with 6.1 post-burn * Burnt site (fire scar) exhibited a warmer (~2°C) and a drier atmosphere near the surfaceLand surface modification by fire of tropical savanna and feedbacks to climate - N.J. Tapper, V. Clayton, J. Beringer, A. Lynch, C. Wendt, and L. B. Hutley, Monash University, Melbourne, Australia. (http://ams.confex.com/ams/Annual2005/techprogram/paper_82869.htm)Fire and Smoke
  • Laboratory Experiment
  • In addition to the output of and the distance from the energy source, surface
  • type (surface reflectivity, specific heat, etc.) affect the absorption of incident
  • radiation and how incident energy changes the temperature of a surface.
  • In this lab you will examine the effect of various types of “surfaces” on the time
  • rate of change of temperature of those surfaces when they are exposed to
  • incident “sunlight”. Recall that an object’s change in temperature,T, is related
  • to the object’s mass, M, the specific heat of the object, csh, and the energy the
  • object absorbs and uses to change its temperature, E, i.e.,
  • T = E / ( csh M ) .
  • Surface reflectivity impacts the amount of incident radiation that is used to change the surface’s temperature, i.e., the surface’s reflectivity contributes to determiningE in the above relationship. For example, if the surface were highly reflective, then little of the incident radiation would be absorbed and used to warm the surface. Mathematically, we can express this relationship for a dry surface as
  • E = (1 - Albedo ) * (Incident Radiation),
  • where Albedo is defined as the fraction of incident energy that is reflected, i.e., albedo is the amount of electromagnetic energy reflected divided by the amount of incident energy.
  • Fire and SmokeWhat are the local climate effects of a fire?Smoke and aerosol particles from fires can rise high into the troposphere and be carried long distances by the wind. Smoke plumes from Mexico have traveled as far north as Wisconsin and the Dakotas, and as far east as Florida and out over the Gulf Stream.Effects of aerosols represent one of the greatest uncertainties regarding climate change, both on global and regional scales. August 13, 2007http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17744http://earthobservatory.nasa.gov/Library/GlobalFire/fire_4.htmlAugust 13, 2007http://earthobservatory.nasa.gov/NaturalHazards/natural_hazards_v2.php3?img_id=14443Fire and SmokeWhat are the local climate effects of a fire?Scientists do not fully understand the magnitude of their cooling influence on climate. Scientists do not know which of the emission products exerts the greater net effect on regional and global climate—the cooling influence of aerosols and clouds, or the warming influence of the greenhouse gases. Because both types of emission products change rapidly through time and space, they are difficult to observe and characterize. In the future, the greenhouse gas warming is expected to dominate due to the gases' much longer presence in the atmosphere (10-100 yrs.) than that of aerosol particles (7 days).http://earthobservatory.nasa.gov/Library/GlobalFire/fire_4.htmlIncoming SolarRadiation 100% Total Albedo 30%6% Scatteredby Air4% Reflectedfrom Surface20% Reflectedby Clouds25% Direct3% Absorbedby Clouds16% Absorbedby Air 26% Diffuse51% Absorbed at theEarth's SurfaceFire and SmokeHow does smoke affect the solar radiation budget? Typically, the “direct effect” of most smoke is to increase the atmospheric reflectivity as compared to that which would have occurred without the aerosols.
  • Note: If smoke, clouds or other aerosols increase the atmospheric albedo, then
  • the percent of incoming
  • solar radiation scattered
  • will increase,
  • - less energy will reach
  • the Earth’s surface,
  • - the surface will not get
  • as warm.
  • Fire and SmokeHow does smoke affect the solar radiation budget? (Con’t)However, soot or “black carbon” smoke, which is generated from traffic, industrial pollution, outdoor fires and household burning of coal and biomass fuels, behaves diffe
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