Tabove: Compute temperature above canopy

In ilyamaclean/microctools: Various worker functions for microclimc package

Compute temperature above canopy

Description

Function to compute air temperature above canopy.

Usage

Tabove(
  climdata,
  z,
  lat,
  long,
  hgt,
  pai,
  x = 1,
  gsmax = 0.33,
  slope = 0,
  aspect = 0,
  alb = 0.23,
  galb = 0.15,
  zu = 2,
  Bowen = 1.5,
  upper = 25,
  umin = 0.5,
  merid = 0,
  dst = 0,
  clump = 0,
  method = "S",
  lims = "FALSE"
)

Arguments

climdata	a dataframe of hourly weather data formated and with units as per the internal dataset climdata
z	height above canopy for which temperature estimate is required (m)
lat	the latitude of the location (decimal degrees)
long	the longitude of the location (decimal degrees)
hgt	canopy height (m)
pai	the total one sided area of canopy elements per unit ground area (see details)
x	leaf distribution angle coefficient
gsmax	maximum stomatal conductance of leaves (mol / m^2 / s)
slope	the slope of the underlying ground surface (decimal degrees). Ignored if method = S.
aspect	the aspect of the underlying ground surface (decimal degrees). Ignored if method = S.
alb	the albedo of the canopy surface (either the combined ground and canopy albedo if method = S or just the canopy albedo)
galb	ground surface albedo
zu	the height above ground of wind speeds in climdata (m)
Bowen	Optional parameter specifying the Bowen Ratio of the surface. Used to improve estimates of temperature in application of the Penman-Monteith equation
upper	optional upper limit to temperature offset (difference between reference and canopy surface temperature cannot exceed this value). Ignored if lims = FALSE
umin	optional minimum wind speed for computing conductances (avoids conductances being too low)
merid	an optional numeric value representing the longitude (decimal degrees) of the local time zone meridian (0 for GMT)
dst	an optional numeric value representing the time difference from the timezone meridian (hours, e.g. +1 for BST if merid = 0).
clump	clumpiness factor (0-1, see details)
method	if S treats the vegetation surface as a flat surface (see details)
lims	optional logical indicating whether to limit temperatures by upper and dewpoint temperature

Details

if pai is unknown it can be estimated as -ln(1-fractional canopy cover). if clump = 0 the canopy is assumed entirely uniform and radiation transmission is as for a turbid medium. As clump approaches 1, the canopy is assumed to be increasingly patchy, such that a greater proportion of reaches the ground without being obscured by leaves. If method = S, the radiation intercepted by the canopy is assumed to be that for a flat surface. If method is not S, the radiation absorption by the gorund and canopy surface are computed separately accounting for the inclination of the ground surface and the distribution of leaf angles.

Value

a vector of air temperatures (deg C) above canopy

Examples

# Compute temperature offset of reference surface
Tref<-Tabove(climdata,1,50.2178,-5.32656,hgt=0.5,pai=2,gsmax=0.33,alb=0.23)
dTRef<-Tref-climdata$temp
# Compute temperature offset of different surface
Th<-Tabove(climdata,1,50.2178,-5.32656,hgt=0.25,pai=1.5,gsmax=0.43,alb=0.15)
dTh<-Th-climdata$temp
# Check whether offsets are linearly related to one another
plot(dTh~dTref,pch=15)
abline(lm(dTh~dTref),lwd=2,col="red")

ilyamaclean/microctools documentation built on Jan. 25, 2023, 5:29 a.m.