Estimate Relative Humidity from Air Temperature and Dew Point Temperature

Computes relative humidity (%) from air temperature and dew point temperature using the Magnus-Tetens approximation. This is the inverse of dew_point().

Usage

relative_humidity(temperature, dewpoint, na.action = c("na.pass", "na.fail"))

Arguments

temperature: Numeric. Air temperature (°C). Must have the same length as dewpoint; inputs are not recycled.
dewpoint: Numeric. Dew point temperature (°C). Should not exceed 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. Relative humidity (%), between 0 and 100 when dewpoint <= temperature, with the same length as the inputs. If either input is entirely missing, the result is entirely NA.

Details

Relative humidity is the ratio of the saturation vapour pressure at the dew point to that at the air temperature:

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

with $a = 17.62$ and $b = 243.12$ (Alduchov and Eskridge, 1996).

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

# Relative humidity for 10 °C air temperature and 6.7 °C dew point
relative_humidity(10, 6.7)
#> [1] 79.96699

# Vectorized input
relative_humidity(c(5, 10, 15), c(3.5, 4.8, 4.7))
#> [1] 90.03161 70.11943 50.16902