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Boundary-Layer Meteorology and Atmospheric Dispersion

Boundary-Layer Meteorology and Atmospheric Dispersion. Dr. J. D. Carlson Oklahoma State University Stillwater, Oklahoma. Mechanisms of Heat Transfer in the Atmosphere-Earth System. Radiation (no conducting medium) Sensible Heat Transfer (large-scale movement of heated material)

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Boundary-Layer Meteorology and Atmospheric Dispersion

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  1. Boundary-Layer Meteorology and Atmospheric Dispersion Dr. J. D. Carlson Oklahoma State University Stillwater, Oklahoma

  2. Mechanisms of Heat Transferin the Atmosphere-Earth System • Radiation (no conducting medium) • Sensible Heat Transfer (large-scale movement of heated material) • Latent Heat Transfer (change of phase associated with water) • Conduction (molecule to molecule)

  3. RADIATION in the Earth-Atmosphere System

  4. Shortwave Radiation Longwave Radiation SUN EARTH

  5. Shortwave Longwave

  6. THE GREENHOUSE EFFECT

  7. MERCURY Sunlit Side = 800 F Dark Side = -279 F NO Greenhouse Effect (no atmosphere)

  8. VENUS Surface Temp = 900 F Large Greenhouse Effect (atmosphere is 97% CO2)

  9. RADIATION AT THE EARTH’S SURFACE SW SW LW LW • Shortwave (solar) radiation reaches a portion of the earth’s surface (SW ) • A portion of that solar is reflected back (SW ) • Albedo (α) = the fraction of solar radiation reflected (SW = αSW ) • Albedo values: Dark soil 0.05-0.15 • Dry sand 0.25-0.40 • Meadow 0.10-0.20 • Forest 0.10-0.46 • Water 0.05-0.10 • Fresh snow 0.7-0.9 • Old snow 0.4-0.7 • The surface receives longwave (infrared) radiation from the sky (LW ) • The surface emits longwave radiation to the sky (LW ) • The sum of the four radiation terms is often called “Net Radiation” (R)

  10. SURFACE ENERGY BUDGET (How is the net radiation partitioned at the earth’s surface ?)

  11. SURFACE ENERGY BUDGET SW = shortwave radiation received SW = shortwave radiation reflected LW = longwave radiation received LW = longwave radiation emitted H = sensible heat transfer by turbulence, advection, convection LE = latent heat transfer (change of phase: evaporation, condensation, freezing, thawing) G = heat transfer through the submedium (conduction) SW + SW + LW + LW + H + LE + G = rate of warming or cooling of surface LE DAY G Energy Units +20 -4 +4 -11 -1 -4 -2 = +2 (surface warming) +9 -7 NIGHT LE G Energy Units +4 -11 +1 +3 +1 = -2 (surface cooling) +5 -7

  12. ATMOSPHERIC BOUNDARY LAYER Daily Behavior under High Pressure Regimes

  13. Typical Vertical Profiles of Wind and Temperature during the Course of a 24-h Fall Day with Clear Skies (note formation and growth of temperature inversion during the night) “Inversion” = temperature increases with height T2, z2 LAPSE RATE ∂TT2 – T1 ∂z z2 – z1 T1, z1 =

  14. T2, z2 LAPSE RATE ∂TT2 – T1 ∂z z2 – z1 T1, z1 =

  15. Surface Radiation Inversion

  16. Temperature Profile Radiation Inversion

  17. Subsidence Inversion HIGH PRESSURE

  18. Temperature Profile Subsidence Inversion

  19. ATMOSPHERIC DISPERSION 1. General mean air motion that transports the pollutant a. horizontally - “advection” b. vertically - “convection” 2. Turbulence - random velocity fluctuations that disperse the pollutant in all directions 3. Molecular diffusion - due to concentration gradients

  20. TURBULENCE • Mechanical (wind-related) • 2. Thermal (temperature-related)

  21. MECHANICAL TURBULENCE • Speed shear • Directional shear • Surface frictional effects

  22. THERMAL TURBULENCE

  23. DENSITY DEPENDS ON TEMPERATURE Ideal Gas Law: PV = nRT (P = pressure, V = volume, n = # moles, R = Universal gas constant, T = Absolute Temp) Can be rewritten: P = rRT, where r = Density For two air parcels at the same pressure, the warmer parcel has the lower density: r= P / RT

  24. ADIABATIC LAPSE RATE (rate of temperature change that an air parcel experiences as it changes elevation without any heat exchange) (dT/dz)adiab = Γ = - g/cp =-1C/100 m = -5.4F/1000 ft z T

  25. ENVIRONMENTAL LAPSE RATE (actual rate of temperature change with height of the current atmosphere) (∂T/∂z)env = environmental lapse rate z T

  26. (∂T/∂z)env = Γ (∂T/∂z)env > Γ (∂T/∂z)env < Γ

  27. THERMAL STABILITY (∂T/∂z)env < Γ Unstable (∂T/∂z)env = Γ Neutral (∂T/∂z)env > Γ Stable

  28. TYPES OF ATMOSPHERIC DISPERSION Weather Factors Side View (vertical dispersion) Top View (horizontal dispersion) UNSTABLE ATMOSPHERE NEUTRAL ATMOSPHERE STABLE ATMOSPHERE

  29. PLUME BEHAVIOR

  30. Unstable Atmosphere –Good Dispersion

  31. LOOPING Γ(adiabatic) environmental Larger scale convective turbulence dominates Strong solar heating with generally light winds Super-adiabatic lapse rates

  32. Neutral Atmosphere –Moderate Dispersion

  33. CONING Γ Near neutral conditions (adiabatic lapse rates) Overcast days or nights Moderate to strong winds Small-scale mechanical turbulence dominates

  34. Stable Atmosphere –Poor Dispersion

  35. FANNING Γ Strong inversion (large positive lapse rate) at plume height Extremely stable conditions (buoyancy suppression) Typical of clear nights with light winds

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