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Explanation of some of the terms used in the bulletins

This page explains some of the jargon that will be encountered when reading our climate bulletins.

Atlantic Multidecadal Oscillation (AMO)

The Atlantic Multidecadal Oscillation (AMO) is variability occurring over many decades that is expressed in the sea surface temperatures of the North Atlantic.

El Niño, La Niña and ENSO (El Niño-Southern Oscillation)

El Niño, La Niña and ENSO (El Niño-Southern Oscillation) are terms that refer to a cycle that occurs naturally in the climate system in the Pacific ocean region of the world near the equator. The cycle involves both the ocean and the atmosphere and has wide-ranging effects. For example it can cause drought and famine in some of the areas that are affected. El Niño and La Niña are opposite states of the cycle. It is possible to see which state the cycle is in by looking at whether the water in the eastern Pacific is warmer or cooler than normal (which identifies El Niño or La Niña states respectively).


Percentiles are used in the bulletins to compare conditions in a particular month to those that were experienced over the reference period of 1961 to 1990. For example if it is said that a temperature anomaly is below the 2nd percentile it means that fewer than two in every hundred months are expected to have lower anomalies in the same location than this month, based on the reference period. Similarly, if the temperature anomaly exceeds the 98th percentile fewer than two in every hundred months are expected to experience a temperature anomaly higher than it, based on the reference period.

Sea surface temperature

Sea surface temperature is a term used for the water temperature at the surface of both the oceans and seas. See also our Surface temperature of the oceans and seas.

Sub-surface ocean temperature

Sub-surface ocean temperature is used when we refer to the three dimensional temperature structure of the ocean as opposed to sea surface temperature, which is restricted to the temperature of the surface only.

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