# dot-get_gtw: g_tw: total conductance to water vapour (m/s) In cdmuir/tealeaves: Solve for Leaf Temperature Using Energy Balance

 .get_gtw R Documentation

## g_tw: total conductance to water vapour (m/s)

### Description

g_tw: total conductance to water vapour (m/s)

### Usage

```.get_gtw(T_leaf, pars, unitless)
```

### Arguments

 `T_leaf` Leaf temperature in Kelvin `pars` Concatenated parameters (`leaf_par`, `enviro_par`, and `constants`) `unitless` Logical. Should function use parameters with `units`? The function is faster when FALSE, but input must be in correct units or else results will be incorrect without any warning.

### Details

Total conductance to water vapor: The total conductance to water vapor (g_tw) is the sum of the parallel lower (abaxial) and upper (adaxial) conductances:

g_tw = gw_lower + gw_upper

The conductance to water vapor on each surface is a function of parallel stomatal (g_sw) and cuticular (g_uw) conductances in series with the boundary layer conductance (g_bw). The stomatal, cuticular, and boundary layer conductance on the lower surface are:

gsw_lower = g_sw (1 - sr) R (T_leaf + T_air) / 2

guw_lower = g_uw / 2 R (T_leaf + T_air) / 2

See `.get_gbw` for details on calculating boundary layer conductance. The equations for the upper surface are:

gsw_upper = g_sw sr R (T_leaf + T_air) / 2

guw_upper = g_uw / 2 R (T_leaf + T_air) / 2

Note that the stomatal and cuticular conductances are given in units of (μmol H2O) / (m^2 s Pa) (see `make_leafpar`) and converted to m/s using the ideal gas law. The total leaf stomatal (g_sw) and cuticular (g_uw) conductances are partitioned across lower and upper surfaces. The stomatal conductance on each surface depends on stomatal ratio (sr); the cuticular conductance is assumed identical on both surfaces.

 Symbol R Description Units Default g_sw `g_sw` stomatal conductance to H2O (μmol H2O) / (m^2 s Pa) 5 g_uw `g_uw` cuticular conductance to H2O (μmol H2O) / (m^2 s Pa) 0.1 R `R` ideal gas constant J / (mol K) 8.3144598 logit(sr) `logit_sr` stomatal ratio (logit transformed) none 0 = logit(0.5) T_air `T_air` air temperature K 298.15 T_leaf `T_leaf` leaf temperature K input

### Value

Value in m/s of class `units`

### Examples

```
# Total conductance to water vapor

## Hypostomatous leaf; default parameters
leaf_par <- make_leafpar(replace = list(logit_sr = set_units(-Inf)))
enviro_par <- make_enviropar()
constants <- make_constants()
pars <- c(leaf_par, enviro_par, constants)
T_leaf <- set_units(300, K)

## Fixing boundary layer conductance rather than calculating
gbw_lower <- set_units(0.1, m / s)
gbw_upper <- set_units(0.1, m / s)

# Lower surface ----
## Note that pars\$logit_sr is logit-transformed! Use stats::plogis() to convert to proportion.
gsw_lower <- set_units(pars\$g_sw * (set_units(1) - stats::plogis(pars\$logit_sr)) * pars\$R *
((T_leaf + pars\$T_air) / 2), "m / s")
guw_lower <- set_units(pars\$g_uw * 0.5 * pars\$R * ((T_leaf + pars\$T_air) / 2), m / s)
gtw_lower <- 1 / (1 / (gsw_lower + guw_lower) + 1 / gbw_lower)

# Upper surface ----
gsw_upper <- set_units(pars\$g_sw * stats::plogis(pars\$logit_sr) * pars\$R *
((T_leaf + pars\$T_air) / 2), m / s)
guw_upper <- set_units(pars\$g_uw * 0.5 * pars\$R * ((T_leaf + pars\$T_air) / 2), m / s)
gtw_upper <- 1 / (1 / (gsw_upper + guw_upper) + 1 / gbw_upper)

## Lower and upper surface are in parallel
g_tw <- gtw_lower + gtw_upper

```

cdmuir/tealeaves documentation built on July 24, 2022, 5:40 a.m.