Humidity is a measure of the amount of water vapor in the air and is a primary element of climate. Humidity can be expressed in a number of ways, including absolute humidity, specific humidity, mixing ratio, relative humidity, and dew point. Although water vapor rarely accounts for more than 4 percent of the total volume of the atmosphere, it is an extremely important component of the atmosphere. Atmospheric water vapor regulates air temperature by affecting the transmission of radiant energy both to and from the earth's surface and provides latent heat energy to fuel storm systems. The maximum amount of water vapor that the atmosphere can hold is a function of the temperature and pressure of the air. The moisture content of air increases rapidly ...