El Niño continues to develop in the tropical Pacific. Forecasters expect the phenomenon to continue into the spring, with 75 up to 85 % chances of it becoming an intense event. A stronger El Niño – The definition of which follows – means it's more likely that we'll see its effects reflected in winter temperatures and rain-and-snow patterns around the world.
Source & screenshots : NOAA – Emily Becker Freely translated.
Atmospheric impact of El Niño
Warning signs
First of all, By the numbers. The main measure of El Niño growth is ocean surface temperature in the region Niño-3.4, an area located in the east-central equatorial Pacific. This region was chosen because it was found to have the strongest relationship with tropical atmospheric changes. Specifically, This is the’Temperature anomaly, that is, the difference between that temperature and the long-term average (long-term = 1991-2020). In September, the Niño-3.4 index was 1,6 °C, according to ERSSTv5, Our most reliable sea surface temperature dataset.
History on 2 years of sea surface temperatures in the Niño-3.4 region of the tropical Pacific for all El Niño events since 1950 (Grey lines) and the current event (Purple Line). NOAA image Climate.gov based on a graph by Emily Becker and monthly CPC Niño-3.4 index data using ERSSTv5.
El Niño is a coupled system, which means that the ocean and the tropical atmosphere work together to keep the El Niño event going on and amplifying. The average pattern of air circulation over the tropical Pacific, called Walker's circulation, Brings in upward air, clouds and storms over the very warm waters of the far western Pacific, West-to-east winds aloft, air descending over the eastern Pacific and surface winds from east to west, called trade winds. In the case of El Niño, warmer-than-average surface waters in the east-central Pacific are causing an increase in upward air in this region, which weakens Walker's circulation (¹).
The atmospheric part of El Niño clearly shows these signs. All indications of a weakening of Walker's circulation are present : More rain and clouds in the east-central Pacific, a slowdown in trade winds and winds at altitude, and drier conditions in Indonesia and the far western Pacific. Overall, ocean surface and atmospheric conditions tell us that El Niño will continue for at least the next few months.
Difference in sea surface temperature in September 2023 compared to the average of 1985-1993 (details from Coral Reef Watch). Most oceans are warmer than average.
Intensification likely
Certain that El Niño will continue throughout the winter, The question is, how strong will it be. Definitions of intensity, typically using Niño-3.4, are not official, because an El Niño with a Niño-3.4 index peaking at 1,5 °C will not have significantly different effects from an El Niño with a Niño-3.4 index of 1,4 °C. However, As mentioned above, the stronger El Niño is, the more likely it is to affect global temperature and rain and snow patterns in the way expected. Indeed, a larger change in sea surface temperature results in a larger change in the Walker circulation, increasing the likelihood that El Niño will affect the jet stream and cause a cascade of global impacts.
The unofficial definition of a strong El Niño is a three-month average Niño-3.4 of at least 1,5 °C. El Niño is a seasonal phenomenon, and this Niño-3.4 index average over three months (called the Niño Ocean Index (or ONI) is important to ensure that ocean and atmospheric changes persist long enough to affect the planet's weather and climate. An ONI peak of 2,0 °C or higher is considered "historically strong" or "very strong". We have only known of four in the historical record since then 1950.
What about a peak at 2,0 °C or higher ? Forecasters give about 3 Odds on 10 for the period November-January. Climate models present a fairly wide range of potential outcomes, if they were concentrated above 2,0 °C, We would probably be able to give more certain probabilities. Otherwise, although there is still a fair amount of heat beneath the surface of the Pacific – This warmer water provides supply to the surface – it's not quite at the level of what we've seen in previous historically strong El Niño's events like 1982-83, 1997-98, or 2015-16.
Each point in this scatter plot shows the subsurface temperature anomaly (Difference from long-term average) in the central tropical Pacific every September (horizontal axis) from 1979 compared to the ENSO oceanic conditions of the following November-January (vertical axis). The red vertical line shows the subsurface temperature anomaly in September 2023. The amount of warmer-than-average water below the surface in September is closely related to ENSO ocean conditions later in the year. Previous strong El Niño events, 1982-83, 1997-98, up to 2015-16, had more hot water below the surface than 2023.
Aggravating factors
Ocean temperatures are still well above average, with astonishing records in recent months.
Non-polar sea surface temperature (60 °N – 60 °S) globally averaged from 1982 up to 2023. Thick black lines represent the average 1982-2011 over the calendar year 2022 (Orange Line), 2023 (Thick Red Line) up to 2016 (The year of record-breaking heat before 2023 Thin Red Line) are highlighted. The fine grey lines represent all other years. Both graphs indicate that the last few months have been marked by record warming of the global ocean
The two graphs above show two different sets of data, one with daily values and the other with monthly averages. Matching two different data sets helps confirm that this is a true characteristic, Therefore reliable.
The extreme heat of the world's oceans – noticeable on these graphs – means that this El Niño is taking place in a different world than previous El Niño. For example, the North Atlantic hurricane season is often quieter during El Niño, But this year, It's already been a busy season, with 18 Named Storms, because the North Atlantic Ocean, hot, provided plenty of fuel.
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(¹) Read the article El Niño is back
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Thanks for sharing the article. Very interesting. Let's see what the impact is on the trade winds