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I was reading the Press Release of World Meteorological Organization press release that was dated March 5, 2024 and I was curious on what they meant by the sentence "The 2023-24 El Niño season has peaked as one of the five strongest on record". What do they mean by that? Did they mean that since 1900 when they recorded El Nino, the 2023-24 El Niño season was the fifth strongest on record recorded by World Meteorological Organization?

ElNino

The article that I'm referring to is:

https://wmo.int/news/media-centre/el-nino-weakens-impacts-continue

Any clarifications will be appreciated. Thank you all!

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  • $\begingroup$ I'm confused what you're asking for clarification on. Are you specifically asking how long they've been measuring it (so 5th stronger in what period)?? $\endgroup$ Mar 14 at 8:39
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    $\begingroup$ @JeopardyTempest That is what I assumed the question is asking (5th strongest in what period, and by what metric), and I answered in that regard. $\endgroup$ Mar 22 at 14:41

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What do they mean by that? Did they mean that since 1900 when they recorded El Nino, the 2023-24 El Niño season was the fifth strongest on record recorded by World Meteorological Organization?

While the World Meteorological Organization did not qualify what they meant by "fifth strongest", apparently they meant since 1950, which is when reliable temperature readings of sea surface temperatures in what is now called the Niño 3.4 region began. The Southern Oscillation Index (SOI), the pressure difference between Tahiti and Darwin Australia, goes back to 1900. The SOI and Oceanic Niño Index (ONI) based on the Niño 3.4 region are strongly but not perfectly correlated (actually, anti-correlated; when the SOI is high the ONI tends to be low, and the other way around). The ONI is now widely used as the measure of whether an El Niño or La Niña is occurring (or about to occur). Here's a chart of strong El Niños since 1950:

Monthly sea surface temperature Niño 3.4 Index values, showing every strong El Niño since 1950
Source: https://www.climate.gov/media/15936

The ENSO blog team at climate.gov wrote this back in December 2023:

We use a three-month average because ENSO is a seasonal phenomenon, meaning it persists for at least several months. We don’t have official strength definitions, but, unofficially, an ONI anomaly of 1.5 °C or warmer is considered a strong El Niño, with 2.0 °C the threshold for “very strong” or “historically strong.”

This was before the current El Niño peaked at just about 2.0 °C, so just at the threshold of "historically strong." From the graph, there are four other El Niños that were clearly stronger than the current one, and one other that also peaked at just about 2.0 °C. However, that other one (1965-1966) peaked a bit early. Using the November to January average, which is widely used as the bellwether indicator of the strength of an El Niño, the current one ranks as the fifth strongest since 1950. However, if one instead uses an "all-winter" point of view, the current one is "only" tied for fifth -- and that's only since 1950.

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