Gb.Su {bigleaf}  R Documentation 
A physically based formulation for the canopy boundary layer conductance to heat transfer according to Su et al. 2001.
Gb.Su(
data,
Tair = "Tair",
pressure = "pressure",
ustar = "ustar",
wind = "wind",
H = "H",
zh,
zr,
d,
z0m = NULL,
Dl,
fc = NULL,
LAI = NULL,
N = 2,
Cd = 0.2,
hs = 0.01,
stab_formulation = c("Dyer_1970", "Businger_1971"),
Sc = NULL,
Sc_name = NULL,
constants = bigleaf.constants()
)
data 
Data.frame or matrix containing all required variables 
Tair 
Air temperature (degC) 
pressure 
Atmospheric pressure (kPa) 
ustar 
Friction velocity (m s1) 
wind 
Wind speed (m s1) 
H 
Sensible heat flux (W m2) 
zh 
Canopy height (m) 
zr 
Reference height (m) 
d 
Zeroplane displacement height (), can be calculated using 
z0m 
Roughness length for momentum (m). If not provided, calculated from 
Dl 
Leaf characteristic dimension (m) 
fc 
Fractional vegetation cover [01] (if not provided, calculated from LAI) 
LAI 
Onesided leaf area index () 
N 
Number of leaf sides participating in heat exchange (defaults to 2) 
Cd 
Foliage drag coefficient () 
hs 
Roughness height of the soil (m) 
stab_formulation 
Stability correction function used (If 
Sc 
Optional: Schmidt number of additional quantities to be calculated 
Sc_name 
Optional: Name of the additional quantities, has to be of same length than

constants 
Kelvin  conversion degree Celsius to Kelvin 
The formulation is based on the kB1 model developed by Massman 1999. Su et al. 2001 derived the following approximation:
kB1 = (k Cd fc^2) / (4Ct ustar/u(zh)) + kBs1(1  fc)^2
If fc (fractional vegetation cover) is missing, it is estimated from LAI:
fc = 1  exp(LAI/2)
The wind speed at the top of the canopy is calculated using function
wind.profile
.
Ct is the heat transfer coefficient of the leaf (Massman 1999):
Ct = Pr^2/3 Reh^1/2 N
where Pr is the Prandtl number (set to 0.71), and Reh is the Reynolds number for leaves:
Reh = Dl wind(zh) / v
kBs1, the kB1 value for bare soil surface, is calculated according to Su et al. 2001:
kBs^1 = 2.46(Re)^0.25  ln(7.4)
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).
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 
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.
Su, Z., Schmugge, T., Kustas, W. & Massman, W., 2001: An evaluation of two models for estimation of the roughness height for heat transfer between the land surface and the atmosphere. Journal of Applied Meteorology 40, 19331951.
Massman, W., 1999: A model study of kB H 1 for vegetated surfaces using 'localized nearfield' Lagrangian theory. Journal of Hydrology 223, 2743.
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.
Gb.Thom
, Gb.Choudhury
, aerodynamic.conductance
# Canopy boundary layer resistance (and kB1 parameter) for a set of meteorological conditions,
# a leaf characteristic dimension of 1cm, and an LAI of 5
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.Su(data=df,zh=25,zr=40,d=17.5,Dl=0.01,LAI=5)
# the same meteorological conditions, but larger leaves
Gb.Su(data=df,zh=25,zr=40,d=17.5,Dl=0.1,LAI=5)
# same conditions, large leaves, and sparse canopy cover (LAI = 1.5)
Gb.Su(data=df,zh=25,zr=40,d=17.5,Dl=0.1,LAI=1.5)