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We often read that El Nino and La Niña occur alternatively. Are they the exact opposite of each other? Or, in other words, can they happen at the same time? (i.e. the whole Pacific Ocean has a higher temperature than normal).

If so, what is the common name of them?

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    $\begingroup$ @Gstesto - you are talking of basin wide warming. That is not the same as El Nino and La Nina occurring at the same time. $\endgroup$ – gansub Jan 26 '17 at 7:38
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    $\begingroup$ No you cannot have both at the same time. They are opposite states of the system. $\endgroup$ – bon Jan 26 '17 at 11:23
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    $\begingroup$ ENSO (El Niño Southern Oscillation) is the appropriate name for the oscillation and both El Niño and La Niña are phases of it. The other phase of the oscillation is called "normal conditions" or ENSO-neutral for lack of a better term. You could read: cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/… $\endgroup$ – arkaia Jan 26 '17 at 14:22
  • $\begingroup$ I know that both hurricanes are made in the Equatorial Pacific at different conditions. $\endgroup$ – MathWA wenti Jan 26 '17 at 23:56
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By definition, El Niño and La Niña cannot occur at the same time. They are instead opposite extreme phases of the El Niño Southern Oscillation.

El Niño conditions occur when the average temperature of the Niño 3.4 region is a half degree or more over the average for three consecutive months or more. La Niña conditions occur when the average temperature is a half degree or more below the average for three consecutive months or more. The reason for looking at a rather narrow band of the equatorial Pacific rather than looking at the Pacific as a whole is because of teleconnections. Whether El Niño, neutral, or La Niña conditions apply has wide ranging impacts across the globe.

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  • $\begingroup$ Defining El Niño with a threshold based on El Niño 3.4 is only part of the story. It all depends on the definition. Clearly you can define a threshold based on MEI (esrl.noaa.gov/psd/enso/mei) (for instance) and the thresholds are going to be different. $\endgroup$ – arkaia Jan 27 '17 at 16:36

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