The atmosphere and the Weather

Temperature and Heat Transfer

Temperature is the quantity that tells us how hot or cold something is relative to some set standard value. But we can look at temperature in another way.

Air is a mixture of countless billions of atoms and molecules. If we could see them, they would appear to be moving about in all directions.

The energy associated with this motion is called kinetic energy, the energy of motion. The temperature of the air (or any substance) is a measure of its average kinetic energy.

Therefore, temperature is a measure of the average speed of the atoms and molecules, where higher energy correspond to faster average speeds.

The atmosphere contains internal energy, which is the total energy stored in its molecules. Heat, on the other hand, is energy in the process of being transferred from one object to another because of the temperature difference between them.

In the atmosphere, heat is transferred by conduction, convection, and radiation.

Conduction	Transfer of heat from molecule to molecule within a substance	Heat transferred in this fashion always flows from warmer to colder regions
Convection	Transfer of heat by the mass movement of the fluid (such as water and air)	This type of heat transfer takes place in liquids because they can move freely and it is possible to set up currents within them
Radiation	Transfer of energy by the emission and absorption of electromagnetic waves (or radiation).	Radiant energy or radiation travels in the form of waves (electromagnetic waves) that release energy when they are absorbed by an object.

The figure below shows some of the different wavelengths of radiation. From that figure we can also see that the longer waves carry less energy than do the shorter ones. In fact, radiation with certain ultraviolet wavelengths has enough radiation to penetrate skin tissue, sometimes causing skin cancer.

Radiation characterized according to wavelength. As the wavelength decreases, the energy carried by the wave increases.

TYPE OF RADIATION	RELATIVE WAVELENGTH	TYPICAL WAVELENGTH (meters)	ENERGY CARRIED PER WAVE
AM radio waves		100
Television waves		1
Microwaves		10-3
Infrared waves		10-6
Visible light		5 x 10-7
Ultraviolet waves		10-7
X rays		10-9

To better understand the concept of radiation, here are a few important concepts and facts to remember:

All things, no matter how big or small, emit radiation. The energy originates from rapidly vibrating electrons, billions of which exist in every object.

The wavelengths of radiation that an object emits depend primarily on the object's temperature. The higher the object's temperature, the shorter are the wavelengths of emitted radiation

Objects that have a higher temperature emit radiation at a greater rate or intensity than objects with a lower temperature. Thus as the temperature of an object increases, more radiation (over a given surface area) is emitted each second.