Mixing ratio

From Glossary of Meteorology

mixing ratio

The ratio of the mass of a variable atmospheric constituent to the mass of dry air.

If not otherwise indicated, the term normally refers to water vapor. For many purposes, the mixing ratio may be approximated by the specific humidity. Either r or w is commonly used to symbolize water vapor mixing ratio, with r used for thermodynamic terms in this glossary. In terms of the pressure p and vapor pressure e, the mixing ratio r is

Compare absolute humidity, relative humidity, dewpoint.