1998 WWLPT Environmental Institute:  Humidity

by  Kathy Gueltzow
      Coral Springs Middle School
      Coral Springs, Florida                                                Return to Humidity Homepage
  

absolute humidity

mass of water vapor (in grams) per unit volume of dry air (in cubic meters), in other words, the density of the water vapor component of air

condensation

water molecules leave the vapor phase and return to the water surface as liquid (net condensation = more return to liquid than vaporize

Dalton's law

total pressure of a mixture of gases equals the sum of the pressures exerted by each constituent gas

deposition

occurs when more water returns to the ice than vaporizes  ( vapor to a solid without a liquid)

humidity

general term referring to any one of a number of ways of specifying the concentration of atmospheric water vapor

evaporation

water molecules escape from the water surface and enter air as vapor  (net evaporation = more water entering the air than returning to liquid)

hydrologic cycle

ceaseless flow of water among the three global reservoirs - ocean, terrestrial, atmosphere

hygrometer

instrument used to measure the water vapor concentration of air

latent heat

quantity of heat that is involved in phase changes

mixing ratio

specifies how much water vapor is mixed with the other atmospheric gases usually expressed as grams of water vapor per kilogram of dry air

precipitable water

amount of water produced when all the water vapor in a column of air condenses

precipitation

rain, drizzle, snow, ice pellets, and hail

psychrometer

an instrument commonly used to measure relative humidity indirectly

relative humidity

compares the actual concentration of water vapor in the air to the concentration of water vapor in that same air at saturation

specific humidity

the ratio of the mass of water vapor (in grams) to the mass (in kilograms) of air containing the water vapor (mass of dry air plus water)

sublimation

occurs when more water enters the vapor phase than returns to ice (solid to vapor without liquid)

transpiration

the process by which water absorbed by plant roots eventually escapes as vapor through tiny pores on the surface of green leaves

vapor pressure

the pressure contributed by water vapor alone and is directly proportional to the concentration of water vapor in air

wet-bulb depression

temperature difference between the two thermometers in a psychrometer

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