The gathering El Niño...

For us, El Niño1 means drought conditions and less snow. Unfortunately the Pacific could well be brewing up a strong one right now. For our 2014 snow season, much depends on how quickly it develops (if it does at all).

The Southern Oscillation Index2 has already plummeted well into El Niño territory, and so far it has stayed down. We need it to bounce, soon:


And the Bureau’s3 numerical modelling is prognosticating a strongish El Niño by later in the year:


Here’s what the Pacific Ocean is currently up to below the surface4, courtesy of the extraordinary Argo system:


That shows a hugely vertically exaggerated east-west cross-section through the tropical Pacific Ocean.  That big lump of unusually hot water5 headed towards South America is called a Kelvin wave, and could be an El Niño in the making.  To understand how, have a look at this nice clear depiction of the mechanics of the 1997-98 El Niño, one of the strongest on record.

It’s early days, but this could easily get ugly.



1. El Niño is one phase of the El Niño Southern Oscillation (ENSO), an east-west quasi-cycle in the tropical Pacific ocean which correlates with precipitation around the world. Yes, around the world — not just snow in Australia, but rain in East Asia, North America, even snow in Siberia. It’s “quasi” because, while it typically shifts every 2-3 years, there’s no evidence of anything fundamentally regular about it. Indeed there’s palaeoclimate evidence that it can sometimes get stuck in one mode or other for decades.

2. The Southern Oscillation Index (SOI) is a simple indicator of ENSO based on the difference between the surface atmospheric pressures in Darwin and Tahiti.

3. The Australian Bureau of Meteorology.

4. From the Climate Prediction Center of the US National Weather Service.

5. The plot is of temperature anomaly; raw temperatures are plotted in the bottom panel here.  What is actually going on there is that the thermocline — the interface between warm surface water and deep cold water — is depressed in a (very) broad trough across the central pacific, and that trough is propagating eastwards as a gravity wave of the (quite small) density difference between warm and cold.  That is the equatorial Kelvin wave.  Such waves are a regular occurrence; it’s just that this one is unusually strong, and badly timed.

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