Weather Notes  Page 1
Section 1-1

Heating the Earth

I.     Weather is a daily condition of the Earth's atmosphere.  The atmosphere is a mixture of gases that surround the Earth.

II.     What causes weather to change?   1.  Heat Energy
                                                                   2.  Air Pressure
                                                                   3.  Winds
                                                                   4.   Moisture

III.  Heat Energy and the Atmosphere

        A.  Almost all of the Earth's energy comes from the sun. This energy is called radiant energy.  The sun's radiant energy helps warm the atmosphere.  Some of the radiant energy from the sun is reflected (bounced back) into space and part of it is scattered back into the atmosphere.  The radiant energy that   is neither reflected nor absorbed by the atmosphere reaches the Earth's surface and changes into heat.

        B.  The sun's energy that is absorbed by the Earth is spread throughout the atmosphere in three basic ways:
               1.  Conduction   2.  Convection   3.  Radiation

        C.  Conduction:  Transfer of heat energy from one substance to another.  The air comes in contact with the warm land and the air is warmed.  (Think of putting your cold hands on a hot mug of coffee.)

        D.  Convection:  Transfer of heat energy in a fluid (gas or liquid).  Air is fluid.  Warm air is less dense so it rises.  Cooler air is more dese so it sinks.  This process causes convection currents.  Most of the heat energy in the atmosphere is transferred by convection currents.  (Think of the furnace on at home and the air in the house is warmed.)

        E.  Radiation:  Transfer of heat energy through empty space.  Radiation does not need the pressence of a solid, liquid, or gas to travel through.  (Think of heat from a light bulb.)

         F.  Ozone gases absorb one form of radiant energy called ultraviolent radiation. Without the ozone layer people would be exposed to higher levels of ultraviolet radiation which can cause skin cancer!