Gb.Choudhury {bigleaf}  R Documentation 
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 s1) 
ustar 
Friction velocity (m s1) 
H 
Sensible heat flux (W m2) 
leafwidth 
Leaf width (m) 
LAI 
Onesided leaf area index 
zh 
Canopy height (m) 
zr 
Instrument (reference) height (m) 
d 
Zeroplane displacement height (), can be calculated using 
z0m 
Roughness length for momentum (m). If not provided, calculated from 
stab_formulation 
Stability correction function used (If 
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

constants 
k  vonKarman constant 
Details
Boundary layer conductance according to Choudhury & Monteith 1988 is given by:
Gb_h = LAI((2a/\alpha)*sqrt(u(h)/w)*(1exp(\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 s1) 
Rb_h 
Boundary layer resistance for heat transfer (s m1) 
kB_h 
kB1 parameter for heat transfer 
Gb_Sc_name 
Boundary layer conductance for 
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 fourlayer model for the heat budget of homogeneous land surfaces. Q. J. R. Meteorol. Soc. 114, 373398.
McNaughton, K. G., Van den Hurk, B.J.J.M., 1995: A 'Lagrangian' revision of the resistors in the twolayer model for calculating the energy budget of a plant canopy. BoundaryLayer Meteorology 74, 261288.
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, 311330.
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)