Diurnal cycles refer to patterns within about a 24-hour period that typically reoccur each day. Most daily cycles are caused by the rotation of the earth, which spins once around its axis about every 24 hours. The term diurnal comes from the Latin word diurnus, meaning daily. Diurnal cycles such as temperature diurnal cycles, diurnal tides, and solar diurnal cycles affect global processes.

A temperature diurnal cycle is composed of the daily rise and fall of temperatures, called the daily march of temperature. The daily rotation of the earth causes the progression of daytime and nighttime, thus controlling the air temperature. The daily maximum temperature occurs between the hours of 2 P.M. and 5 P.M. and then continually decreases until sunrise the next day. The angle of the Sun to the surface of the earth increases until around noon when the angle is the largest. The intensity...