Gb.Choudhury: Boundary Layer Conductance according to Choudhury & Monteith...

In bigleaf: Physical and Physiological Ecosystem Properties from Eddy Covariance Data

Boundary Layer Conductance according to Choudhury & Monteith 1988

Description

A formulation for the canopy boundary layer conductance for heat transfer according to Choudhury & Monteith 1988.

Usage

Gb.Choudhury(
  data,
  Tair = "Tair",
  pressure = "pressure",
  wind = "wind",
  ustar = "ustar",
  H = "H",
  leafwidth,
  LAI,
  zh,
  zr,
  d,
  z0m = NULL,
  stab_formulation = c("Dyer_1970", "Businger_1971"),
  Sc = NULL,
  Sc_name = NULL,
  constants = bigleaf.constants()
)

Arguments

data	Data.frame or matrix containing all required variables
Tair	Air temperature (degC)
pressure	Atmospheric pressure (kPa)
wind	Wind speed at sensor height (m s-1)
ustar	Friction velocity (m s-1)
H	Sensible heat flux (W m-2)
leafwidth	Leaf width (m)
LAI	One-sided leaf area index
zh	Canopy height (m)
zr	Instrument (reference) height (m)
d	Zero-plane displacement height (-), can be calculated using roughness.parameters
z0m	Roughness length for momentum (m). If not provided, calculated from roughness.parameters within wind.profile
stab_formulation	Stability correction function used (If stab_correction = TRUE). Either "Dyer_1970" or "Businger_1971".
Sc	Optional: Schmidt number of additional quantities to be calculated
Sc_name	Optional: Name of the additonal quantities, has to be of same length than Sc_name
constants	k - von-Karman constant Sc_CO2 - Schmidt number for CO2 Pr - Prandtl number (if Sc is provided)

Details

Boundary layer conductance according to Choudhury & Monteith 1988 is given by:

Gb_h = LAI((2a/α)*sqrt(u(h)/w)*(1-exp(-α/2)))

where u(zh) is the wind speed at the canopy surface, approximated from measured wind speed at sensor height zr and a wind extinction coefficient α:

u(zh) = u(zr) / (exp(α(zr/zh -1)))

.

α is modeled as an empirical relation to LAI (McNaughton & van den Hurk 1995):

α = 4.39 - 3.97*exp(-0.258*LAI)

Gb (=1/Rb) for water vapor and heat are assumed to be equal in this package. Gb for other quantities x is calculated as (Hicks et al. 1987):

Gb_x = Gb / (Sc_x / Pr)^0.67

where Sc_x is the Schmidt number of quantity x, and Pr is the Prandtl number (0.71).

Value

A data frame with the following columns:

Gb_h	Boundary layer conductance for heat transfer (m s-1)
Rb_h	Boundary layer resistance for heat transfer (s m-1)
kB_h	kB-1 parameter for heat transfer
Gb_Sc_name	Boundary layer conductance for Sc_name (m s-1). Only added if Sc_name and Sc_name are provided

Note

If the roughness length for momentum (z0m) is not provided as input, it is estimated from the function roughness.parameters within wind.profile. This function estimates a single z0m value for the entire time period! If a varying z0m value (e.g. across seasons or years) is required, z0m should be provided as input argument.

References

Choudhury, B. J., Monteith J.L., 1988: A four-layer model for the heat budget of homogeneous land surfaces. Q. J. R. Meteorol. Soc. 114, 373-398.

McNaughton, K. G., Van den Hurk, B.J.J.M., 1995: A 'Lagrangian' revision of the resistors in the two-layer model for calculating the energy budget of a plant canopy. Boundary-Layer Meteorology 74, 261-288.

Hicks, B.B., Baldocchi, D.D., Meyers, T.P., Hosker, J.R., Matt, D.R., 1987: A preliminary multiple resistance routine for deriving dry deposition velocities from measured quantities. Water, Air, and Soil Pollution 36, 311-330.

See Also

Gb.Thom, Gb.Su, aerodynamic.conductance

Examples

## bulk canopy boundary layer resistance for a closed canopy (LAI=5) 
## with large leaves (leafwdith=0.1)            
df <- data.frame(Tair=25,pressure=100,wind=c(3,4,5),ustar=c(0.5,0.6,0.65),H=c(200,230,250))    
Gb.Choudhury(data=df,leafwidth=0.1,LAI=5,zh=25,d=17.5,zr=40)

## same conditions, but smaller leaves (leafwidth=0.01)
Gb.Choudhury(data=df,leafwidth=0.01,LAI=5,zh=25,d=17.5,zr=40) 

bigleaf documentation built on Aug. 22, 2022, 9:09 a.m.