Canopy layer to canopy layer aerodynamic conductance

Compute the aerodynamic conductance for sensible and latent heat between canopy layers following Van de Griend and Van Boxel (1989).

G_interlay(
  Wind,
  ZHT,
  Z_top,
  Z0 = Z_top * 0.1,
  ZPD = Z_top * 0.75,
  alpha = 1.5,
  ZW = ZPD + alpha * (Z_top - ZPD),
  LAI_top,
  LAI_bot,
  extwind = 0,
  vonkarman = Constants()$vonkarman
)

Arguments

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: `0.1*Z_top`
ZPD	Zero-plane displacement (m), Default: `0.75*Z_top`
alpha	Constant for diffusivity at top canopy. Default: `1.5` following Van de Griend et al (1989).
ZW	Top height of the roughness sublayer (m). Default: `ZPD+alpha*(Z_top-ZPD)`
LAI_top	Leaf area index of the upper layer (m2 leaf m-2 soil).
LAI_bot	Leaf area index of the layer below the upper layer (m2 leaf m-2 soil).
extwind	Extinction coefficient. Default: `0`, no extinction.
vonkarman	Von Karman constant, default to `Constants()$vonkarman`, 0.41.

Value

g_af

The aerodynamic conductance of the air between two canopy layers (m s-1)

Details

alpha can also be computed as: $$alpha=\frac{zw-d}{Z_{top}-d}$$ The aerodynamic conductance between canopy layers is computed as: $$g_{af}= \frac{1}{\frac{U_h}{K_h}\ln(U_{mid}/U_{inter})}$$ where usually $U_{mid}$ is the wind speed at (median) cumulated LAI between the top and the soil, and $U_{inter}$ the wind speed at the height between the two canopy layers. In this function, $U_{mid}$ and $U_{inter}$ are computed relative to the leaf area instead of the height of the vegetation layers.

References

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.

Examples