Diurnal cycle
A diurnal cycle is any pattern that recurs every 24 hours as a result of one full rotation of the Earth.

In climatology
Climatology is the study of climate, scientifically defined as weather conditions averaged over a period of time, and is a branch of the atmospheric sciences...

, the diurnal cycle is one of the most basic forms of climate pattern
Climate pattern
A climate pattern is any recurring characteristic of the climate. Climate patterns can last tens of thousands of years, like the glacial and interglacial periods within ice ages, or repeat each year, like monsoons....

s. The most familiar such pattern is the diurnal temperature variation
Diurnal temperature variation
Diurnal temperature variation is a meteorological term that relates to the variation in temperature that occurs from the highs of the day to the cool of nights.-Temperature lag:Temperature lag is an important factor in diurnal temperature variation...

. Such a cycle may be approximately sinusoidal, or include components of a truncated sinusoid (due to the sun's rising and setting).

Practical Example

In telecommunications, the daily temperature cycle from the sun warming the earth causes a diurnal sinusoidal phase shift as the fiber optics or wire cabling expands and contracts.
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