relative humidity

https://doi.org/10.1351/goldbook.R05267
The ratio, often expressed as a percentage, of the @P04420@ of water in the atmosphere at some observed temperature, to the @S05479@ of pure water at this temperature.
Source:
PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2210 [Terms] [Paper]