What is the El Niño–Southern Oscillation (ENSO) in a nutshell?
Go to any agency that is focused on weather or climate forecasting and you’ll hear scientists buzzing to one another about “ENSO” (pronounced “en-so”). After glancing at the stereotypical scientist, you might immediately assume “En-so” is a Star Wars character, but you would be mistaken. ENSO is one of the most important climate phenomena on Earth due to its ability to change the global atmospheric circulation, which in turn, influences temperature and precipitation across the globe. We also focus on ENSO because we can often predict its arrival many seasons in advance of its strongest impacts on weather and climate.
Though ENSO is a single climate phenomenon, it has three states, or phases, it can be in. The two opposite phases, “El Niño” and “La Niña,” require certain changes in both the ocean and the atmosphere because ENSO is a coupled climate phenomenon. “Neutral” is in the middle of the continuum.
- El Niño: A warming of the ocean surface, or above-average sea surface temperatures (SST), in the central and eastern tropical Pacific Ocean. Over Indonesia, rainfall tends to become reduced while rainfall increases over the tropical Pacific Ocean. The low-level surface winds, which normally blow from east to west along the equator (“easterly winds”), instead weaken or, in some cases, start blowing the other direction (from west to east or “westerly winds”).
- La Niña: A cooling of the ocean surface, or below-average sea surface temperatures (SST), in the central and eastern tropical Pacific Ocean. Over Indonesia, rainfall tends to increase while rainfall decreases over the central tropical Pacific Ocean. The normal easterly winds along the equator become even stronger.
- Neutral: Neither El Niño or La Niña. Often tropical Pacific SSTs are generally close to average. However, there are some instances when the ocean can look like it is in an El Niño or La Niña state, but the atmosphere is not playing along (or vice versa).
So, by now, you might have noticed that while “ENSO” is a nice catchall acronym for all three states, that acronym doesn’t actually have the word La Niña in it. Why is that? Well, that is a fluke of history. Before La Niña was even recognized, South American fisherman noticed the warm up of coastal waters occurred every so often around Christmas. They referred to the warming as “El Niño,” (niño being Spanish for a boy child) in connection with the religious holiday.
Sir Gilbert Walker discovered the “Southern Oscillation,” or large-scale changes in sea level pressure across Indonesia and the tropical Pacific. However, he did not recognize that it was linked to changes in the Pacific Ocean or El Niño. It wasn’t until the late 1960s that Jacob Bjerknes and others realized that the changes in the ocean and the atmosphere were connected and the hybrid term “ENSO” was born. It wasn’t until the 1980s or later that the terms La Niña and Neutral gained prominence.
In future updates, we will spend more time describing ENSO and how it is defined and tracked, but if you can’t wait, you can read more here now.
But, if you just want to keep things simple, then watch Chris Farley play El Niño on Saturday Night Live.
Comments
Congratulations
Excellent description. I have been promoting this site among the oceanography students in Chile (all fields of oceanography and marine biology) after my friend David Legler recommended it on his facebook.
Good job.
Is always difficult to find one site where people (in general) can get a good overview and understandable description of ENSO.
rnunez@srf.cl
RE: Congratulations
Great description as we here in Southern California are going to get wet !!! Real wet ......
average ocean temperatures
If El Nino is a difference between average ocean temperatures and the SST at particular place/time, then as ocean temperatures rise in response to global warming the absolute temperature/ heat content bar for calling an El Nino must rise. And, a moderate El Nino of today reflects more ocean basin heat than a moderate El Nino of 40 years ago?
If, on an absolute basis, modern El Ninos are driven by larger heat pools then El Ninos of the past, do modern El Ninos have more effect on the global climate? Or, is everything relative, and they have no more effect because everything else is warmer. Or, do the non-linear effects of water vapor dominate, and more water vapor in the air changes everything?
Re: Average Ocean Temperatures
One of our scienitsts will have to weigh in on the second part of your question, but regarding part 1, we did an article on the subject of how global warming has forced NOAA to re-define what counts as "average" for the purpose of monitoring El Niño.
http://www.climate.gov/news-features/understanding-climate/watching-el-n...
RE: Re: Average Ocean Temperatures
1. Thank you so much for the illuminating the El-Nino and La Nina phenomena. Is there a deeper root cause to these phenomena or it is just chaotic?
1. I looked at the page you referenced for what is "average" ocean surface temperature during October November range and I got the impression that the temperature average during 30 years preceded 2005 are warmer than the 30 years preceded 2010. This is in conflict to the global warming concept. Isn't that right?
Thank you
Shmuel
RE: RE: Re: Average Ocean Temperatures
Not an expert, but I thought best way to look at things would be as climate change, not so much global warming. Then things still make sense.
El Nino graphics
Great graphics on El Nino and La Nina. Could you also include the average jet stream acros the Pacific durin both an El Nino and La Nina event?
And, why this stroNg EL NINO, this year?
Is "EL NINO" so stronger this year because of "global warming?
RE
It look like September is ending!
ElNino in a nutshell by Michelle L'Heureux .
I have been a So Ca resident for 75 years and am quite familiar with the terms "El Nino" and "La Nina". I must say Ms. L'Heureux's article really did put the entire phenomenon in a perspective that was understandable to the non-scientific mind. I am hopeful we receive a bountiful level of precipitation this winter. Thank you.
Quick Question
Will El Nina carry swine flu?
RE: Quick Question
First, did you mean El Nino or La Nina? In either case, the answer is probably not much, at least directly. But if either one of them indirectly causes populations to migrate more, as might also be the case for general climate change, then there could be an exacerbating effect on incidence of swine flu.
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