El Niño

I must confess to not knowing very much at all about ENSO (El Niño Southern Oscillation), but while making the animations of Hadcrut4 I noticed some striking examples. Here for example is the ‘super’ el Nino of 1997/98.

The strong El Nino which developed in second half of 1997 resulting in record temperatures in 1998.

The strong El Niño which developed in second half of 1997 resulting in record temperatures in 1998. Also Note that in these maps that I am using a neutral light-grey colour for DT < ± 0.5C

Every 6-10 years an area of warm water appears off the coast of South America around autumn time with consequent effects on global  weather patterns. What is causing this ?

When I was a small boy I played a game in the bath of sloshing water backwards and forwards until it overflowed, much to the annoyance of my mother.  El Nino seems to be the same effect in the pacific ocean with the trades winds playing the role of the little boy.

el Nino. The easterly trades 'slosh' warm water up against indonesia. Eventually it sloshes back again.

el Nino. The easterly trades ‘slosh’ warm water up against indonesia. Eventually it sloshes back again.

Unfortunately that is not why El Niño means ‘Little boy’ in Spanish. It got this name because fishermen in Chile noticed that the warm water always seemed to appear before  Christmas – the birth of Christ – el Nino!

During normal (la Nina?) years the trade winds blow westerly causing  water to build up in the warmer western pacific. Gravity eventually sloshes this warm water back to the east which weakens the trade winds and the temperature equalizes, before the whole cycle repeats itself.  The net effect is a warming of the atmosphere and a temporary shifting  of evaporation/convection  zones.  Such events can be seen throughout the Hadcrut4 series and  el Nino always to begins to show in the Autumn normally lasting through the winter months. For example here is another  strong el Nino  seen during 1982

1982 saw a strong El Nino develop

1982 saw a strong Ekl Nino develop

and further examples are seen in 1972

Strong El Nino in 1972

Strong El Nino in 1972

and in 1965

1965

1965

or even in 1957
frame107

and 1930 !

Even further back  clear el Nino’s can be found in the data in  1913/14 1904/1905 1896/7

The earliest example I can find is in 1888/89 even though the SST measurements were then very sparse.

1888 shows clear signs of El Nino despite the very sparse coverage

1888 shows clear signs of El Nino despite the very sparse coverage of SST measurements

The fact that this last event from 127y ago is still visible in the sparse Hadcrut4 data is remarkable, but also says something rather subtle about the effective magnitude of global warming locally. The colours shown in all plots are relative to the normalised ’30y climate’ period 1961-1990, so any place showing red is actually warmer than the average temperatures 1961-1990 which is something like 100y after start of the industrial revolution. In 1980 CO2 levels were already 360 ppm yet clear past El Nino’s are still visible as red stripes in the pacific all the way back to 1870. This means that localized El Nino warming in the eastern pacific is far greater than anything produced so far by global warming. Likewise localised seasonal temperature variations in northern continents are larger than net warming as well, since otherwise there would be no red areas evident early on.

Temperature anomalies relative to average February temperatures between 1961-1990.

Temperature anomalies relative to the average February temperatures between 1961-1990.

The next 10 years should be interesting.

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5 Responses to El Niño

  1. Fernando L. says:

    Dont forget the upwelling cold water has a tendency to cool the eastern pacific. I like to sit and watch a reanalysis product swirl on the screen, and it shows El Niño is a warm period because that cold water just doesnt seem to come up. But maybe I’m wrong?

  2. opluso says:

    Typos:

    During normal (la Nina?) years the trade winds blow easterly causing water to build up in the warmer EASTERN pacific. Gravity eventually sloshes this warm water back to the WEST which weakens the trade winds and the temperature equalizes, before the whole cycle repeats itself.

    (emphasis added)

    During normal years the WESTERN Pacific is warmer and sea levels much higher than the eastern (i.e., coastal South America) Pacific. As your images correctly indicate, El Nino is defined by warm surface waters moving to the eastern Pacific. And as long as I’m proofreading, your animation suggests that warm water sloshes over Panama into the Caribbean. Although I suppose that if the isthmus was, in fact, missing it would indeed change regional (and probably global) climate.

    Nonetheless, your point about relative warmth in the early temperature record is an important one. Nice work.

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