surface.conditions {bigleaf}

Big-Leaf Surface Conditions

Description

Calculates meteorological conditions at the big-leaf surface by inverting bulk transfer equations for water, energy, and carbon fluxes.

Usage

surface.conditions(
  data,
  Tair = "Tair",
  pressure = "pressure",
  LE = "LE",
  H = "H",
  VPD = "VPD",
  Ga = "Ga_h",
  calc.surface.CO2 = FALSE,
  Ca = "Ca",
  Ga_CO2 = "Ga_CO2",
  NEE = "NEE",
  Esat.formula = c("Sonntag_1990", "Alduchov_1996", "Allen_1998"),
  constants = bigleaf.constants()
)

Arguments

data

Data.frame or matrix containing all required input variables

Tair

Air temperature (deg C)

pressure

Atmospheric pressure (kPa)

LE

Latent heat flux (W m-2)

H

Sensible heat flux (W m-2)

VPD

Vapor pressure deficit (kPa)

Ga

Aerodynamic conductance for heat/water vapor (m s-1)

calc.surface.CO2

Calculate surface CO2 concentration? Defaults to FALSE.

Ca

Atmospheric CO2 concentration (mol mol-1). Required if calc.surface.CO2 = TRUE.

Ga_CO2

Aerodynamic conductance for CO2 (m s-1). Required if calc.surface.CO2 = TRUE.

NEE

Net ecosystem exchange (umol m-2 s-1). Required if calc.surface.CO2 = TRUE.

Esat.formula

Optional: formula to be used for the calculation of esat and the slope of esat. One of "Sonntag_1990" (Default), "Alduchov_1996", or "Allen_1998". See Esat.slope.

constants

cp - specific heat of air for constant pressure (J K-1 kg-1)
eps - ratio of the molecular weight of water vapor to dry air (-)
Pa2kPa - conversion pascal (Pa) to kilopascal (kPa)

Details

Canopy surface temperature and humidity are calculated by inverting bulk transfer equations of sensible and latent heat, respectively. 'Canopy surface' in this case refers to the surface of the big-leaf (i.e. at height d + z0h; the apparent sink of sensible heat and water vapor). Aerodynamic canopy surface temperature is given by:

Tsurf = Tair + H / (\rho * cp * Ga)

where \rho is air density (kg m-3). Vapor pressure at the canopy surface is:

esurf = e + (LE * \gamma)/(Ga * \rho * cp)

where \gamma is the psychrometric constant (kPa K-1). Vapor pressure deficit (VPD) at the canopy surface is calculated as:

VPD_surf = Esat_surf - esurf

CO2 concentration at the canopy surface is given by:

Ca_surf = Ca + NEE / Ga_CO2

Note that Ga is assumed to be equal for water vapor and sensible heat. Ga is further assumed to be the inverse of the sum of the turbulent part and the canopy boundary layer conductance (1/Ga = 1/Ga_m + 1/Gb; see aerodynamic.conductance). Ga_CO2, the aerodynamic conductance for CO2 is also calculated by aerodynamic.conductance. If Ga is replaced by Ga_m (i.e. only the turbulent conductance part), the results of the functions represent conditions outside the canopy boundary layer, i.e. in the canopy airspace.

Value

a data.frame with the following columns:

Tsurf

Surface temperature (deg C)

esat_surf

Saturation vapor pressure at the surface (kPa)

esurf

vapor pressure at the surface (kPa)

VPD_surf

vapor pressure deficit at the surface (kPa)

qsurf

specific humidity at the surface (kg kg-1)

rH_surf

relative humidity at the surface (-)

Ca_surf

CO2 concentration at the surface (umol mol-1)

Note

The following sign convention for NEE is employed (relevant if calc.surface.CO2 = TRUE): negative values of NEE denote net CO2 uptake by the ecosystem.

References

Knauer, J. et al., 2018: Towards physiologically meaningful water-use efficiency estimates from eddy covariance data. Global Change Biology 24, 694-710.

Blanken, P.D. & Black, T.A., 2004: The canopy conductance of a boreal aspen forest, Prince Albert National Park, Canada. Hydrological Processes 18, 1561-1578.

Shuttleworth, W. J., Wallace, J.S., 1985: Evaporation from sparse crops- an energy combination theory. Quart. J. R. Met. Soc. 111, 839-855.

Examples

# calculate surface temperature, water vapor, VPD etc. at the surface
# for a given temperature and turbulent fluxes, and under different 
# aerodynamic conductance.
surface.conditions(Tair=25,pressure=100,LE=100,H=200,VPD=1.2,Ga=c(0.02,0.05,0.1)) 
         
# now calculate also surface CO2 concentration
surface.conditions(Tair=25,pressure=100,LE=100,H=200,VPD=1.2,Ga=c(0.02,0.05,0.1),
                   Ca=400,Ga_CO2=c(0.02,0.05,0.1),NEE=-20,calc.surface.CO2=TRUE)