PBLreview - Review of PBL dynamics Balance of the dynamic...

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Review of PBL dynamics Balance of the dynamic forces within the PBL • Neutral homogeneous surface layer • Non-neutral homogeneous surface layer • Roughness sublayer over homogeneous plant and urban canopy • Inhomogeneous urbane canopy • Convective mixing layer and stable nighttime BL Similarity theories for these layers Simple bulk transfer models Impacts of PBL on land surface and free atmosphere
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Change in dynamic balance from surface to free atmosphere: Homogeneous surface roughness layer roughness surface layer over plant canopy Roughness surface layer over urban canopy Roughness surface layer over inhomogeneous surface " u t # $ u ' w ' z turbulent drag u t # $ 1 % p ' x + f v $ u ' w ' z turbulent drag u t # $ 1 p ' x + f v
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The MO surface layer: Surface roughness and shear driven turbulence dominate the transport. The shear generated TKE is locally dissipated by viscosity of the air. The mixing can be treated like a diffusion. For a neutral surface layer K m " # u z = $ o = u * o 2 u = u * o k ln z + cons tan t For a non-neutral surface layer : kz u *o u z = % M ( ) where M ( ) is stability function, M ( ) =1, neutral M ( ) > 0, stable, M ( ) < 0, unstable, unstable stable neutral The MOS uses a stability parameter, ζ , to determine the deviation from the logarithmic profile:
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The ratio of buoyancy driven and shear driven turbulent flux, ζ , determine the deviation from the logarithmic profile: " # z/L = - g $ ( w ' ' ) o u * 3 / kz ( ) z/L < 0 for unstable surface layer z/L > 0 for stable surface layer ~ R f # g v ( w ' v ' ) u ' w ' % u z + v ' w ' v z notice that Rf can be applied to entire ABL, not necesarily linked to u * .whereas is defined for surface layer and closely linked to u * . also kz v * o #" v # z = H ( ) where H ( ) is the stability function for heat kz q * o q z = W ( ) where W ( ) is the stability function for humidity
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The influence of surface stress, u *o, and roughness, z o : MOS is mainly valid for ζ ~ 1-2, and weakly stable or unstable; For near neutral condition, Φ ( ζ )=1+ β 1 ζ + β 2 ζ 2 +... 1+ β 1 ζ The integral form of the MOS: Z o : surface aerodynamic roughness length u = u * o k ln( z z o ) + " 1 # Roughness, z o , increases For very stable case ( ζ→ ʿ± , turbulence is suppressed, u is influenced by stability , not by z o , z-less; For very unstable case ( ζ→ - ʿ± , MOS scaling becomes invalid. The bulk transfer coefficient, C
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This note was uploaded on 11/07/2011 for the course EAS 8803 taught by Professor Staff during the Spring '08 term at Georgia Institute of Technology.

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PBLreview - Review of PBL dynamics Balance of the dynamic...

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