Compute the aerodynamic conductance for sensible and latent heat between the center of the lowest canopy layer and the soil surface following Van de Griend and Van Boxel (1989).
G_soilcan( Wind, ZHT, Z_top, Z0 = Z_top * 0.1, ZPD = Z_top * 0.75, alpha = 1.5, ZW = ZPD + alpha * (Z_top - ZPD), LAI, extwind = 0, vonkarman = Constants()$vonkarman )
| Wind | Average daily wind speed above canopy (m s-1) |
|---|---|
| ZHT | Wind measurement height (m) |
| Z_top | Average canopy height of the taller crop (m) |
| Z0 | Roughness length (m). Default: |
| ZPD | Zero-plane displacement (m), Default: |
| alpha | Constant for diffusivity at top canopy. Default: |
| ZW | Top height of the roughness sublayer (m). Default: |
| LAI | Total leaf area index above the soil (m2 leaf m-2 soil). |
| extwind | Extinction coefficient. Default: |
| vonkarman | Von Karman constant, default to |
The aerodynamic conductance of the air between the lowest canopy layer and the soil surface (m s-1)
alpha can also be computed as:
$$alpha=\frac{zw-d}{Z_{top}-d}$$
The aerodynamic conductance between the lowest canopy layer and the soil
is computed as:
$$g_{a0}= \frac{1}{\frac{U_h}{K_h}\ln(U_{mid}/U_{0})}$$
where \(U_{mid}\) is the wind speed at median cumulated LAI between the top and the soil, and
\(U_0\) the wind speed at soil surface.
Van de Griend, A.A. and J.H. Van Boxel, Water and surface energy balance model with a multilayer canopy representation for remote sensing purposes. Water Resources Research, 1989. 25(5): p. 949-971.
# G_a0 for a coffee plantation managed in agroforestry system: G_soilcan(Wind= 1, ZHT= 25, Z_top= 24,LAI= 4.5, extwind= 0.58)#> [1] 1.172889