pvlib.atmosphere.rh_from_tdew

pvlib.atmosphere.rh_from_tdew(temp_air, temp_dew, coeff=(6.112, 17.62, 243.12))

Calculate relative humidity from dewpoint temperature using the Magnus equation.

Parameters:

• temp_air (numeric) – Air temperature (dry-bulb temperature). [°C]

• temp_dew (numeric) – Dew-point temperature. [°C]

• coeff (tuple, default (6.112, 17.62, 243.12)) – Magnus equation coefficients (A, B, C). The default values are those recommended by the WMO [1].

Returns:

numeric – Relative humidity (0.0-100.0). [%]

Notes

Relative humidity is computed as 100 * e / es, where e is the saturation vapor pressure at the dew point temperature, and es is the saturation vapor pressure at the air temperature, both from the Magnus equation A * exp(B * T / (C + T)). The default coefficients (A, B, C) = (6.112, 17.62, 243.12) are the WMO-recommended Magnus form for saturation over liquid water, valid for temperatures from -45 to +60 °C [1]; see [2] for the approximation and its accuracy.

References

[1] (1,2)

“Guide to Instruments and Methods of Observation”, World Meteorological Organization, WMO-No. 8, 2023. https://library.wmo.int/idurl/4/68695

[2]

O. A. Alduchov and R. E. Eskridge, “Improved Magnus Form Approximation of Saturation Vapor Pressure”, Journal of Applied Meteorology, 35(4), pp. 601-609, 1996.