Gb.Choudhury {bigleaf}

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/\alpha)*sqrt(u(h)/w)*(1-exp(-\alpha/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 \alpha:

u(zh) = u(zr) / (exp(\alpha(zr/zh -1)))

.

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

\alpha = 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)