wetbulb.temp {bigleaf}

Wet-Bulb Temperature

Description

calculates the wet bulb temperature, i.e. the temperature that the air would have if it was saturated.

Usage

wetbulb.temp(
  Tair,
  pressure,
  VPD,
  accuracy = 0.001,
  Esat.formula = c("Sonntag_1990", "Alduchov_1996", "Allen_1998"),
  constants = bigleaf.constants()
)

Arguments

Tair

Air temperature (deg C)

pressure

Atmospheric pressure (kPa)

VPD

Vapor pressure deficit (kPa)

accuracy

Accuracy of the result (deg C)

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) Le067 - Lewis number for water vapor to the power of 0.67

Details

Wet-bulb temperature (Tw) is calculated from the following expression:

e = Esat(Tw) - Le067 * gamma * (Tair - Tw)

The equation is solved for Tw using optimize. Actual vapor pressure e (kPa) is calculated from VPD using the function VPD.to.e. The psychrometric constant gamma (kPa K-1) is calculated from psychrometric.constant. Le067 is the Lewis number for water vapor to the power of 0.67 and represents the ratio of aerodynamic resistance to water vapor and heat. Le067 * gamma is sometimes referred to as the 'modified psychrometric constant (gamma*).

Value

Tw -

wet-bulb temperature (degC)

References

Monteith J.L., Unsworth M.H., 2013: Principles of Environmental Physics. Plants, Animals, and the Atmosphere. 4th edition. Academic Press.

Examples

wetbulb.temp(Tair=c(20,25),pressure=100,VPD=c(1,1.6))