The sun in the ultimate source of energy in the atmosphere.  Energy is transfered from the sun through space by a process called radiation.  Radiant energy does not require contact between two objects nor does it require a gas or liquid medium for transfer. 

     The sun's energy  travels in the form  of an electromagnetic spectrum. The wavelengths of interest to meteorologists are the range between the infrared waves and the ultraviolet waves.

     As the sun's energy enters Earth's atmosphere,  most of the ultraviolet rays are absorbed by the thermosphere, mesosphere, and ozone layer of the stratosphere.  Some UV radiation continues through to the Earth's surface.

     Visible light includes the wavelengths that we associate with colors. These are red, yellow, blue, and violet.  Orange and green are variations of these.

     Earth's atmosphere traps infrared energy from the sun as thermal energy or heat.  The Earth radiates heat back into the atmosphere.  The atmosphere reflects heat back to Earth.  This is a delicate balance called the greenhouse effect.  Too much heat is a runaway greenhouse effect and leads to conditions common during the early history of the planet.  Too little trapped heat can lead to an ice  age.

The short blue wavelength of visible light is scattered as it enters Earth's atmosphere.  This scattering gives the sky it's blue appearance during the day. 

At sunrise and sunset, the blue light tends to "skip" over the outer layers of the atmosphere or enter at a shallow angle.  Thus, the red and yellow wavelengths are seen at those times of day.  That is why the sky appears to be glow red and orange.

Temperature is a measure of the average kinetic energy of the molecules of a substance. 

Heat is thermal energy or energy associated with the movement of molecules.

The three ways of transfering heat are radiation, convection, and conduction.

Heat Transfer by Radiation

Radiation is a transfer of thermal energy that does not require contact or a medium such as a gas or liquid. The sun transfers energy through the vacuum of space by radiation.

Heat Transfer by Conduction

Conduction requires direct contact between the objects or the object and heat source.  The electric heating coil of a stove transfers heat to a metal pan by conduction.

Heat Transfer by Convection

Convection is heat transfer through a gas or liquid.  The heated air or liquid molecules move to a cooler area setting up convection currents.

Energy PowerPoint

Heat Transfer PowerPoint