Calculate dewpoint temperature

Calculate dewpoint temperature \(T_d\) (°C) from air temperature \(T\) (°C) and relative humidity \(RH\) (%).

Usage

cal_dewpoint_temperature(rh, t, t_unit)

Arguments

rh

Numeric. Relative humidity in %, from 0 to 100.

t

Numeric. Air temperature in degree Celsius (°C), degree Fahrenheit (°F), or Kelvin (K).

t_unit

Character string. Unit of the temperature value. Must be one of "celsius", "fahrenheit", or "kelvin".

Value

Numeric value of dewpoint temperature in degree Celsius (°C).

Details

The dewpoint temperature \(T_d\) (°C) is the temperature at which air becomes saturated (relative humidity reaches 100%). This function uses the approximation derived from the Clausius–Clapeyron equation:

$$e_s = 6.108 \cdot exp(\frac{17.27 \cdot T}{T + 237.3})$$

$$T_d = \frac{237.3 \cdot \ln\left(\frac{e_s \cdot RH}{611}\right)}{7.5 \cdot \ln(10) - \ln\left(\frac{e_s \cdot RH}{611}\right)}$$

where:

• \(T\) is air temperature (°C),

• \(e_s\) is the saturation vapor pressure in hPa,

• \(RH\) is relative humidity in %.

The temperature input is converted to degree Celsius (°C) based on the provided t_unit before calculation.

References

National Weather Service. Wet-bulb Temperature and Dewpoint Temperature from Air Temperature and Relative Humidity. Retrieved from https://www.weather.gov/media/epz/wxcalc/wetBulbTdFromRh.pdf

See also

weathermetrics::humidity.to.dewpoint(), weathermetrics::dewpoint.to.humidity(), cal_saturation_vapor_pressure(), cal_relative_humidity()

Examples

cal_dewpoint_temperature(rh = 39.7, t = 28, t_unit = 'celsius')
#> [1] 13.02466
cal_dewpoint_temperature(rh = 42.8, t = 20, t_unit = 'celsius')
#> [1] 6.979868