The ratio of vapor pressure to saturated vapor pressure. A measure of how close the air is to being saturated at a given temperature, this measurement aids in determining the rate of evaporation.
The ratio of the mass of water vapor in a given volume of air, or the density of water vapor. This measurement is actually not used by meteorologist, but instead, is used often in engineering.
The ratio of the mass of water vapor to the total mass of moist air. This measurement only changes by the addition or subtraction of water vapor.
The temperature to which air must be cooled to become saturated at the constant atmospheric pressure. At this temperature, water vapor will begin to condense.
A measure of the depth of liquid water if all the water vapor in the atmosphere condenses in a column of air over a given location.