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  • Canopy turbulence  (2)
  • Springer  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Modelling Vegetation-Atmosphere Co2 Exchange By A Coupled Eulerian-Langrangian Approach (2000)
    Springer
    Boundary layer meteorology 95 (2000), S. 91-122 
    Details
    ISSN: 1573-1472
    Keywords: Canopy turbulence ; Lagrangian stochastic model ; Turbulence closure ; Canopy photosynthesis ; Carbon dioxide ; Radiation attenuation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A Eulerian-Lagrangian canopy microclimate model wasdeveloped with the aim of discerning physical frombiophysical controls of CO2 and H2O fluxes. The model couples radiation attenuation with mass,energy, and momentum exchange at different canopylevels. A unique feature of the model is its abilityto combine higher order Eulerian closure approachesthat compute velocity statistics with Lagrangianscalar dispersion approaches within the canopy volume. Explicit accounting for within-canopy CO2,H2O, and heat storage is resolved by consideringnon-steadiness in mean scalar concentration andtemperature. A seven-day experiment was conducted inAugust 1998 to investigate whether the proposedmodel can reproduce temporal evolution of scalar(CO2, H2O and heat) fluxes, sources andsinks, and concentration profiles within and above auniform 15-year old pine forest. The modelreproduced well the measured depth-averaged canopy surfacetemperature, CO2 and H2O concentrationprofiles within the canopy volume, CO2 storageflux, net radiation above the canopy, and heat andmass fluxes above the canopy, as well as the velocitystatistics near the canopy-atmosphere interface. Implications for scaling measured leaf-levelbiophysical functions to ecosystem scale are alsodiscussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002473906184
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Spatial Variability of Turbulent Fluxes in the Roughness Sublayer of an Even-Aged Pine Forest (1999)
    Springer
    Boundary layer meteorology 93 (1999), S. 1-28 
    Details
    ISSN: 1573-1472
    Keywords: Canopy turbulence ; Moving equilibrium hypothesis ; Planar homogeneity ; Roughness sublayer ; Spatial variability ; Turbulent fluxes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The spatial variability of turbulent flow statistics in the roughness sublayer (RSL) of a uniform even-aged 14 m (= h) tall loblolly pine forest was investigated experimentally. Using seven existing walkup towers at this stand, high frequency velocity, temperature, water vapour and carbon dioxide concentrations were measured at 15.5 m above the ground surface from October 6 to 10 in 1997. These seven towers were separated by at least 100m from each other. The objective of this study was to examine whether single tower turbulence statistics measurements represent the flow properties of RSL turbulence above a uniform even-aged managed loblolly pine forest as a best-case scenario for natural forested ecosystems. From the intensive space-time series measurements, it was demonstrated that standard deviations of longitudinal and vertical velocities (σu, σw) and temperature (σT) are more planar homogeneous than their vertical flux of momentum (u* 2) and sensible heat (H) counterparts. Also, the measured H is more horizontally homogeneous when compared to fluxes of other scalar entities such as CO2 and water vapour. While the spatial variability in fluxes was significant (〉15 %), this unique data set confirmed that single tower measurements represent the ‘canonical’ structure of single-point RSL turbulence statistics, especially flux-variance relationships. Implications to extending the ‘moving-equilibrium’ hypothesis for RSL flows are discussed. The spatial variability in all RSL flow variables was not constant in time and varied strongly with spatially averaged friction velocity u*, especially when u* was small. It is shown that flow properties derived from two-point temporal statistics such as correlation functions are more sensitive to local variability in leaf area density when compared to single point flow statistics. Specifically, that the local relationship between the reciprocal of the vertical velocity integral time scale (Iw) and the arrival frequency of organized structures (ū/h) predicted from a mixing-layer theory exhibited dependence on the local leaf area index. The broader implications of these findings to the measurement and modelling of RSL flows are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002079602069
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