of the atmosphere is greater in winter than in summer because of the greater differences in temp. in winter. Large bodies of water tend to stabilize air temps. much more than land masses do. On land, heat penetrates very little - most of the heat is at or near the surface. In water, however, the heat penetrates deeper because of water's translucence. Also, turbulence in water tends to distribute the heat more evenly. The evaporation at the surface requires heat from water. All these factors tend to keep water temps. more nearly constant. Physical properties of air Heating or cooling of air (by expansion or compression) occurs without any exchange of heat with the outside. This is called adiabatic change, and is thermally isolated. Any air that rises, expands; it is compressed when it descends. Movement of air occurs so rapidly that it is considered adiabatic (no transfer of heat). The capacity of air to hold water vapor decreases rapidly as the air is cooled. Precipitation occurs with the cooling of moist air. Boyle's Law - for a constant temp., the volume of dry gas varies inversely as the pressure. Charles' Law - for a constant pressure, the volume of dry gas is directly proportional to the absolute temp. Expanding mass of air is cooled to the extent of the increase in volume. A contracting mass of air is heated by the work of compression performed on it. Temperature changes are considerable under these conditions. For example: an air mass expanded to 1/2 its initial pressure reduces the absolute temp. by 18%