The partial pressure of vapor pv is the product of the saturation pressure psat and the relative humidity phi:

The saturation concentration csat is obtained from the saturation pressure psat and temperature T by

where R is the universal gas constant.

The humidity ratio xvap is obtained from the vapor and air concentrations cv and ca, the absolute pressure pA and temperature T by

where R is the universal gas constant, Mv is the water vapor molar mass, and Ma is the dry air molar mass.

The vapor mass fraction omega_v is obtained by

The total moisture concentration cw is the sum of the liquid water and vapor concentrations cl and cv:

Note that cl=0 in moist air domains.

The liquid water and vapor contents wc_l and wc_v are obtained by multiplying the concentrations cl and cv by the molar mass of water M_v:

The moisture content wcVar is expressed in different ways depending on the domain type:

The variable Lv is defined by

where T is the temperature. See Functions for the definition of the function Lv.