Roughness Sublayer and Canopy Layer turbulent profiles over tall vegetation. Ricardo K. Sakai D. R. Fitzjarrald Matt Czikowsky University at Albany, SUNY. Surface Layer. Inertial sublayer. Cross section from Laser Vegetation Imaging Sensor (LVIS). Constant Flux. Roughness sublayer.
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Ricardo K. Sakai
D. R. Fitzjarrald
University at Albany, SUNY
Cross section from Laser Vegetation Imaging Sensor (LVIS)
Rugosity = f(canopy topography)
Wind Tunnel tall vegetation
Canopy area densities (CAD, , where PAI is the plant area index) for (a) for wind tunnel (Raupach et al., 1986), (b) HF foliated (Parker, personal communication), (c) HF leafless (Parker, personal communication), (d) coniferous forest (Halldin, 1985), (e) Amazon forest (Roberts et al., 1994) (f) Oak Ridge (Meyers and Baldocchi, 1991), (g) almond orchard (Baldocchi and Hutchison, 1988), (h) Camp Borden (Neumann et al., 1989).
CANOPY LAYER tall vegetation
where h is the mean canopy height.
PAI is plant area index
CAD is the canopy area distribution
σ tall vegetationw /u*vsz/h
MOS value in IL
σ tall vegetationU /u*vsz/h
MOS value in IL
u tall vegetation*(z/h)/u*(1) vsz/h
Roughness Sublayer tall vegetation
For a broad leaf forests: tall vegetation
Displacement height (d) - mean level of momentum absorption (Thom, 1971):
Traditional: New approach:
Therefore: dc=0.7 h (Deciduous - Broad leaf forests)
dc=0.6 h (sparse coniferous) - numerically
σ tall vegetationwvsz/h
MOS value in the IL
Skw tall vegetation(w) vsz/h
Skw(w) vs (z –dc)/(h-dc)
Skewness in the lower CBL
Fitted curve (above canopy): tall vegetation
Spectral Analysis tall vegetation
Drowning in spectra, craving cospectra
Cospectral shape in RSL: tall vegetation
-5/3 power law
Moraes et al., accepted in Physica A
Dimensionless frequency: tall vegetation
Above canopy: z > h → z’= z-dc
Inside canopy: z < h → z’= h-dc
Conclusions: tall vegetation
Seeking similarity rules for tall canopies.
Scaling length is (h-dc(CAD)) in the RSL for several forests
Canopy Layer (several forests):
- The use of the canopy area density helps to differentiate broad leaves from coniferous forests, approaching to a more “universal relationship”.
To improve, rugosity?
Roughness sublayer (several forests):
- Ratio [(z-dc)/(h- dc)] is about 2.4 to 3.5
- Scaling to (z-d)/(h-d) gives better generalization.
- Skewness of w profile is a good indicator of the RSL
Spectral analysis (only HF):
- best scaling is (h-dc) within the canopy.
- “Short circuit”/wake effect only during the foliated period
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Gryanik and Hartmann,2002,JAS
Fig. 4. (a), (c) Skewness of the vertical wind velocity and (b), (d) the temperature. (a) and (b) Full dots represent the Reynolds-averaged skewness and open circles the mass-flux skewness [Eq. (10)] of the aircraft data. Solid lines are the LES results of free convection of MGMOW. The ordinates show normalized height. (c), (d) Mass-flux vs Reynolds skewness of the aircraft data. The ratio of the mass-flux to Reynolds skewness is 0.30 for Sθ and 0.31 for Sw, but the correlation is very low. De Laat and Duynkerke (1998) found a ratio of 0.25 for Sw for a stratocumulus case