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.
A climate pattern may come in the form of a regular cycle, like the diurnal cycle or the seasonal cycle; a quasi periodic event, like El Niño; or a highly irregular event, such as a volcanic winter. The regular cycles are generally well understood and may be removed by normalization. For example, graphs which show trends of temperature change will usually have the effects of seasonal variation removed.
Modes of variability
A mode of variability is a climate pattern with identifiable characteristics, specific regional effects, and often oscillatory behavior. Many modes of variability are used by climatologists as indices to represent the general climatic state of a region affected by a given climate pattern.
Measured via an empirical orthogonal function analysis, the mode of variability with the greatest effect on climates worldwide is the seasonal cycle, followed by El Niño-Southern Oscillation, followed by thermohaline circulation.
Other well-known modes of variability include: