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.
Roughness Sublayer and Canopy Layer turbulent profiles over tall vegetation
Ricardo K. Sakai
D. R. Fitzjarrald
University at Albany, SUNY
Cross section from Laser Vegetation Imaging Sensor (LVIS)
Rugosity = f(canopy topography)
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).
where h is the mean canopy height.
PAI is plant area index
CAD is the canopy area distribution
MOS value in IL
MOS value in IL
For a broad leaf forests:
Displacement height (d) - mean level of momentum absorption (Thom, 1971):
Therefore: dc=0.7 h (Deciduous - Broad leaf forests)
dc=0.6 h (sparse coniferous) - numerically
MOS value in the IL
Skw(w) vs (z –dc)/(h-dc)
Skewness in the lower CBL
Fitted curve (above canopy):
Drowning in spectra, craving cospectra
Cospectral shape in RSL:
-5/3 power law
Moraes et al., accepted in Physica A
Above canopy: z > h → z’= z-dc
Inside canopy: z < h → z’= h-dc
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
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