Leaf boundary layer conductance for heat

Compute the bulk leaf boundary layer conductance for heat using the wind speed, the leaf dimension, and leaf area distribution following Jones (1992) or Leuning et al. (1995).

Gb_h(
  Wind,
  wleaf = 0.068,
  LAI_lay,
  LAI_abv,
  extwind = 0,
  Z_top,
  ZHT,
  Z0 = Z_top * 0.1,
  ZPD = Z_top * 0.75,
  alpha = 1.5,
  ZW = ZPD + alpha * (Z_top - ZPD),
  Tleaf = NULL,
  Tair = NULL,
  Dheat = Constants()$Dheat,
  formulation = c("Jones_1992", "Leuning_1995")
)

Arguments

Wind	Average daily wind speed above canopy (m s-1)
wleaf	Average leaf width (m)
LAI_lay	Leaf area index of the layer (m2 leaves m-2 soil)
LAI_abv	Cumulated leaf area index above the layer (m2 leaves m-2 soil)
extwind	Extinction coefficient. Default: `0`, no extinction.
Z_top	Average canopy height of the taller crop (m)
ZHT	Wind measurement height (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)`
Tleaf	Leaf temperature (deg C). Only needed if `formulation="Leuning_1995"`
Tair	Canopy air temperature (deg C). Only needed if `formulation="Leuning_1995"`
Dheat	Molecular diffusivity for heat (m2 s-1). Default to `Constants()$Dheat`. Only needed if `formulation="Leuning_1995"`
formulation	The formulation used to compute $Gb_h$

Value

The leaf boundary layer conductance for heat (m s-1)

Details

The leaf boundary layer conductance for heat can be transformed into leaf boundary layer conductance for water vapour as follow: $$Gb_w= 1.075*gb_h$$ Note that $Gb_w$ should be doubled for amphistomatous plants (stomata on both sides of the leaves).

References

Leuning, R., et al., Leaf nitrogen, photosynthesis, conductance and transpiration: scaling from leaves to canopies. Plant, Cell & Environment, 1995. 18(10): p. 1183-1200.
Mahat, V., D.G. Tarboton, and N.P. Molotch, Testing above‐ and below‐canopy represetations of turbulent fluxes in an energy balance snowmelt model. Water Resources Research, 2013. 49(2): p. 1107-1122.

Examples