Calculate Relative Humidity from temperature and dew point

Function to calculate relative humidity (%) from temperature (°C) and dew point (°C)

Usage

calcRH_DP(Temp, DewP, method = c("Magnus", "Buck"))

Arguments

Temp: Temperature (°Celsius)
DewP: Td (DP), Dew Point (°Celsius)
method: Calculation method: either "Magnus" or "Buck". Defaults to "Magnus".

Value

Relative Humidity (0-100%)

Details

This function supports two methods for relative humidity calculation:

"Magnus" (default): Uses the August-Roche-Magnus approximation, valid for 0°C < Temp < 60°C and 1% < RH < 100%.
"Buck": Uses the Arden Buck equation with Bögel modification, valid for -30°C < Temp < 60°C and 1% < RH < 100%.

The methods calculate temperature based on vapor pressure and saturation vapour pressure relationships. The Magnus method is chosen as the default because it is more stable when used with the calcDP and calcTemp functions.

References

Alduchov, O. A., and R. E. Eskridge, 1996: Improved Magnus' form approximation of saturation vapor pressure. J. Appl. Meteor., 35, 601–609

Buck, A. L., 1981: New Equations for Computing Vapor Pressure and Enhancement Factor. J. Appl. Meteor. Climatol., 20, 1527–1532, https://doi.org/10.1175/1520-0450(1981)020<1527:NEFCVP>2.0.CO;2.

Buck (1996), Buck (1996), Buck Research CR-1A User's Manual, Appendix 1.

https://bmcnoldy.earth.miami.edu/Humidity.html

Examples

# RH at air tempertaure of 20°C and dew point of 15°C
calcRH_DP(20, 15)
#> [1] 72.93877
calcRH_DP(20, 15, method = "Buck")
#> [1] 73.17992

calcRH_DP(20, calcDP(20, 50))
#> [1] 50

calcRH_DP(20, calcDP(20, 50, method = "Buck"), method = "Buck")
#> [1] 50

# mydata file
filepath <- data_file_path("mydata.xlsx")
mydata <- readxl::read_excel(filepath, sheet = "mydata", n_max = 5)

mydata |>
  dplyr::mutate(
    DewPoint = calcDP(Temp, RH),
    RH_default = calcRH_DP(Temp, DewPoint),
    RH_Buck = calcRH_DP(Temp, DewPoint, method = "Buck"))
#> # A tibble: 5 × 8
#>   Site   Sensor Date                 Temp    RH DewPoint RH_default RH_Buck
#>   <chr>  <chr>  <dttm>              <dbl> <dbl>    <dbl>      <dbl>   <dbl>
#> 1 London Room 1 2024-01-01 00:00:00  21.8  36.8     6.38       36.8    36.8
#> 2 London Room 1 2024-01-01 00:15:00  21.8  36.7     6.34       36.7    36.7
#> 3 London Room 1 2024-01-01 00:29:59  21.8  36.6     6.30       36.6    36.6
#> 4 London Room 1 2024-01-01 00:44:59  21.7  36.6     6.22       36.6    36.6
#> 5 London Room 1 2024-01-01 00:59:59  21.7  36.5     6.18       36.5    36.5