description symbol units
composite parameter (Q – 2εσTa4λgtwDa) a J m-2 s-1
composite parameter (8εσTa3 + cpagbh + λgtws) b J m-2 s-1 K-1
ratio of adaxial to abaxial boundary layer resistance in abscence of hairs β -
heat capacity of air cpa J mol-1 K-1
difference between leaf and air temperature δ K
water vapor mole fraction deficit of the air Da mol mol-1
final value of δ δf K
depth of hair (trichome) layer dh m
binary diffusivity for heat in air Dha m2 s-1
initial value of δ δi L
leaf size (characteristic dimension) dl m
leaf dry mass DM g
leaf to air water vapor mole fraction difference Δw mol mol-1
leaf thermal emissivity ε -
boundary layer conductance to heat gbh mol m-2 s-1
leaf surface conductance to water vapor gsw mol m-2 s-1
leaf total conductance to water vapor gtw mol m-2 s-1
leaf heat capacity k J m-2 K-1
latent heat of vaporization λ J mol-1
leaf area LA m2
absorbed radiation Q J m-2 s-1
gas constant R Pa m3 mol-1 K-1
resistance added by hairs at one leaf surface rh m2 s mol-1
derivative of ws with respect to temperature s mol mol-1 K-1
Stefan-Boltzmann constant σ J m-2 s-1 K-4
leaf temperature T K
air temperature Ta K
wind speed vw m s-1
ambient water vapor mole fraction wa mol mol-1
leaf fresh mass WM g
saturated value of water vapor mole fraction ws mol mol-1
water use efficiency WUE mmol mol-1
time constant for leaf cooling τ s