There are 3 states of water which are liquid, solid and gas. All three states exist on earth. Water has been called the life force. There are names for each of the phase changes of water. They are given below: Water going from a solid to a liquid: Melting Water going from a liquid to a gas: Evaporation Water going from a solid to a gas: Sublimation Water going from a liquid to a solid: Freezing Water going from a gas to a liquid: Condensation Water going from a gas to a solid: Deposition In each phase change there will be either an absorption or release of latent heat. Latent heat absorption cools the surrounding air while latent heat release warms the surrounding air. Below are each process and whether it absorbs or releases latent heat: Melting: absorbs latent heat Evaporation: absorbs latent heat Sublimation: absorbs latent heat Freezing: releases latent heat Condensation: releases latent heat Deposition: releases latent heat With each phase change a specific amount of latent heat is released or absorbed. Below are the values in two different scales which are calories per gram (cal/g) and Joules per kilogram (J/kg). Releasing latent heat is designated as a positive number and absorbing latent heat as a negative number in this listing to make it easier to see relative direction of heat flow relative to surrounding air. Melting: -79.7 cal/g, -330,000 J/kg Evaporation: -597.3 cal/g, -2,500,000 J/kg Sublimation: -677.0 cal/g, -2,830,000 J/kg Freezing: +79.7 cal/g, +330,000 J/kg Condensation: +597.3 cal/g, +2,500,000 J/kg Deposition: +677.0 cal/g, +2,830,000 J/kg Note that melting and freezing have the same value except the latent heat is flowing in an opposite direction. The same is true for the pairs of evaporation and condensation as well as sublimation and deposition. Also note that the addition of melting and evaporation is the value of sublimation as well as the addition of freezing and condensation is the value of deposition. Note that the magnitude of melting and freezing are much less than the other latent heat processes. Thus melting and freezing do not contribute to cooling and warming the air as much as the other processes. For example, 7.5 times as much cooling occurs from evaporation than it does from melting. These processes contribute to cooling and warming the air in the troposphere. Below is an example for each: Melting: Snow melting in the air as it falls (cools air) Evaporation: Rain evaporating into the air and from the ground when and after it falls (cools air) Sublimation: Surface snow vaporizing from the ground while temperature is still below freezing (cools air) Freezing: Liquid cloud droplets being lifted into a very cold subfreezing layer in which they freeze (warms air) Condensation: Liquid cloud developing as air rising by positive buoyancy (warms air) Deposition: Frost developing on the ground when temperature is below freezing (warms air) note: warming the air does not always mean an actual increase in temperature but could be a reduction in the amount of cooling. In other words, the latent heat warming is partially offsetting some of the cooling that would take place by another process (i.e. condensation warming partially offsetting adiabatic cooling in a rising saturated air parcel). For a more detailed discussion of the latent heat impact on weather forecasting see the Haby Hints below: http://www.theweatherprediction.com/habyhints/19/ http://www.theweatherprediction.com/habyhints/33/ |