Estimate Dew Point Temperature from Air Temperature and Relative Humidity

Computes the dew point temperature (°C) using the Magnus–Tetens approximation, a widely used empirical relationship between air temperature, relative humidity, and the saturation vapor pressure of water vapor. The method provides a good approximation for typical atmospheric conditions and is suitable for most meteorological and agricultural applications. It works for any air temperature (for example minimum, maximum or mean) with the matching relative humidity. The inverse is relative_humidity().

Usage

dew_point(temperature, rh, na.action = c("na.pass", "na.fail"))

Arguments

temperature: Numeric. Air temperature (°C). Must have the same length as rh; inputs are not recycled.
rh: Numeric. Relative humidity (%) corresponding to temperature.
na.action: Either "na.pass" (the default), which propagates missing values without removing them, or "na.fail", which errors if either input contains NA or NaN.

Value

Numeric. Dew point temperature (°C), with the same length as the inputs. If either input is entirely missing, the result is entirely NA.

Details

The dew point temperature is estimated using the Magnus–Tetens equation:

$$ \gamma = \frac{a \cdot T}{b + T} + \ln\left(\frac{RH}{100}\right) $$ $$ T_{dew} = \frac{b \cdot \gamma}{a - \gamma} $$

where $T$ is air temperature (°C), $RH$ is relative humidity (%), and the empirical constants are $a = 17.62$ and $b = 243.12$ (for water over a liquid surface). This formulation is based on improvements to the original Magnus equation proposed by Alduchov and Eskridge (1996).

For air temperatures below 0 °C, slightly different coefficients are sometimes used to account for ice surfaces, but the above constants are generally suitable for most temperature ranges encountered in agricultural or meteorological data.

References

Alduchov, O. A., & Eskridge, R. E. (1996). Improved Magnus Form Approximation of Saturation Vapor Pressure. Journal of Applied Meteorology, 35(4), 601–609. doi:10.1175/1520-0450(1996)035<0601:IMFAOS>2.0.CO;2

Examples

# Dew point for 10 °C and 80% RH
dew_point(10, 80)
#> [1] 6.706013

# Vectorized input
dew_point(c(5, 10, 15), c(90, 70, 50))
#> [1] 3.495014 4.775543 4.651626