El Niño–Southern Oscillation
El Niño–Southern Oscillation (ENSO) is an irregularly periodical variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean, affecting much of the tropics and subtropics. The warming phase is known as El Niño and the cooling phase as La Niña. Southern Oscillation is the accompanying atmospheric component, coupled with the sea temperature change: El Niño is accompanied with high, and La Niña with low air surface pressure in the tropical western Pacific. The two periods last several months each (typically occur every few years) and their effects vary in intensity (info courtesy of Wikipedia).
Figure 1 – Courtesy of NCOF
The coastal waters off the coast of Chile seem to have cooled down since last month. There were SST anomalies 0f +5°C on the chart for the 18th of March last month (fig 1), but the highest that I can see in the same area is +3°C twenty five days later (fig 2). The experts are saying that an El Niño event still remains a distinct possibility towards the end of this year though.
Figure 2 – Courtesy of NCOF
I’m no expert and don’t pretend to understand why the cold Humboldt current seems to be the controlling mechanism for the upwelling of warmer water off the coast of Chile (fig 3).
Figure 3 – Courtesy of Wikipedia
But this map I found after a little research on the Internet indicate that there are more than just the Humboldt current at play down the coast of South America (fig 4).
Figure 4 – Courtesy of CALEB
I shall of course try to find out and report back, unless one of my readers would like to do it for me.
Figure 1 – Data courtesy of NOAA/ESRL
The statistics that are used to decide whether we are currently in a La Niña or an El Niño event, or if conditions are just neutral, never fail to amuse me. I thought I’d correctly programmed all the rules into my application, but obviously you need to be monitoring more areas of the Pacific than region 3.4 that I do. As far as I make it, conditions over the last 5 months in region 3.4, meant that a La Niña event had started in August (fig 2). Three month averaged SST anomalies have been below -0.5°C for the required five consecutive months, and as far as I could see that was it, bingo. But not so, the event didn’t even happen according to the experts, although they do expect that it could start later this year. In my defence, there have been other short five month La Niña and El Niño events in the past, and why this event doesn’t merit being one of those beats me. Meanwhile, I’ll continue to live in my make-believe ENSO world where it did happen, because I refuse to add any more complexity to that application.
Figure 2 – Data courtesy of NOAA/ESRL
Figure 3 (todo: fix the start date one month early) – Data courtesy of NOAA/ESRL
The reason that the La Niña event never really took off, is that some recent warming in the eastern Pacific along the coast of Central America (fig 4), has somehow manage to cut off the supply of colder water that usually tracks from east to west across the equator from the Chilean coast. That’s my very simple explanation, which is almost certainly completely wrong.
Figure 4 – Courtesy of NOAA/ESRL
Courtesy of NOAA
The El Niño event is now history since it ended in May (2016) now it’s just a case of waiting to see if and when La Niña arrives. The region 3.4 index has now been negative for the last two months. But because the index is based on a three-month moving average, and because that average needs to be -0.5 or lower (and we’ve only had the August index lower than that) we might have to wait till the New Year to see if August’s -0.54 is the start of a La Niña event – the Oceanic Niño Index [ONI] calculations are more complex than the majority of the other climate indicators are.
ONI January 1950 – August 2016
Latest SST (courtesy of NOAA-NCEP)
The latest El Niño (for region 3.4) which started back in March 2015 continues into what is highly likely to be its final month of May 2016 according to the latest Oceanic Niño Index [ONI] figures that have just been released. I say that because the ONI is a three-month running mean, and the latest value for region 3.4 during May was +0.30°C which is below the 0.5°C threshold and markedly down on the +1.09°C of the previous month. That’s a duration of 15 months, which could have easily have been four months longer if it weren’t for a stalled start in had. Despite this it still makes it the second longest El Niño in the current series back to 1950, and it also had the highest anomaly of +2.3 of any other event. That still might only make it the second warmest behind the 1997-98 event, but as with everything to do with these cycles it may be down to which region and what algorithm you use to decide these things. It’s interesting to see the cold waters spread across the equator from east to west and splitting the anomalously warm ocean.
El Niño & La Niña Cycles January 1950 – May 2016
Tabulated Oceanic Niño Index [ONI] January 1950 – May 2016
Oceanic Niño Index [ONI] June 1986 – May 2016