Almost all of the energy in the system comes from the sun, which provides us with heat, light, and radiation. Radiant energy travels from the sun, through space and warms the earth's surface. Because the earth is not flat, the sun heats up different parts of it faster than others. For example, a mountainside will only get half the sun a flat desert would get, because it is only in the sun for half of a day, and a flat land would get sun all day, and so the mountainside would be cooler. Water takes much longer to heat up and cool down than land and air do, so water is almost always a separate temperature than the shore or anywhere on land. This differential heating of the earth's surface causes various occurrences in the atmosphere.

Air near land warms up by conduction, and as it heats, expands...