# g_tw: total conductance to water vapour (m/s) ```r .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. ## Returns Value in m/s of class `units` ## 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: $$ g_\mathrm{tw} = g_\mathrm{w,lower} + g_\mathrm{w,upper}g_tw = gw_lower + gw_upper $$ 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: $$ g_\mathrm{sw,lower} = g_\mathrm{sw} (1 - sr) R (T_\mathrm{leaf} + T_\mathrm{air}) / 2gsw_lower = g_sw (1 - sr) R (T_leaf + T_air) / 2 $$ $$ g_\mathrm{uw,lower} = g_\mathrm{uw} / 2 R (T_\mathrm{leaf} + T_\mathrm{air}) / 2guw_lower = g_uw / 2 R (T_leaf + T_air) / 2 $$ See `.get_gbw` for details on calculating boundary layer conductance. The equations for the upper surface are: $$ g_\mathrm{sw,upper} = g_\mathrm{sw} sr R (T_\mathrm{leaf} + T_\mathrm{air}) / 2gsw_upper = g_sw sr R (T_leaf + T_air) / 2 $$ $$ g_\mathrm{uw,upper} = g_\mathrm{uw} / 2 R (T_\mathrm{leaf} + T_\mathrm{air}) / 2guw_upper = g_uw / 2 R (T_leaf + T_air) / 2 $$ Note that the stomatal and cuticular conductances are given in units of ($\mu$mol 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|( $\mu$ mol H2O) / (m $^2$ s Pa)|5| |$g_uw$|`g_uw`|cuticular conductance to H2O|( $\mu$ mol 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| ## Examples ```r # 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 ```

dot-get_gtw function