Moisture & Atmospheric Stability

Minnesota Temperature Conversion Chart

Humidity: Water Vapor in the Air

Ways to express water-vapor (H2O(g)) content of the air:

• absolute humidity
• mixing ratio
• vapor pressure
• relative humidity
• dew point

Water vapor content of air - absolute humidity and mixing ratio are similar. Both are expressed as the quantity of water vapor contained in a specific amount of air.

Under standard conditions (25oC, 1 atm), the density of air is 1.168 kg/m3. Therefore,
1kg of air would have a volume of 0.8562m3. To summarize..... 1kg of air has a volume about 15% smaller than 1m3.

mass of water vapor (grams)

absolute humidity = ---------------------------------

volume of air (cubic meters)

mass of water vapor (grams)

mixing ratio          = ---------------------------------

mass of dry air (kilograms)

vapor pressure

partial pressures & Dalton's Law: the total pressure exerted by a gaseous mixture is equal to the sum of the partial pressures of each individual component in a gas mixture.

saturation - saturation mixing ratio graph

table of saturated mixing ratio

relative humidity

relative humidity calculations with a decrease in temperature DALR   =   - 1.0oC/100m
LHC*    =  +0.5oC/100m
-------------------
WALR  =   - 0.5oC/100m

*Latent Heat of Condensation