With the Australian Bureau of Meteorology declaring an El Niño, and for anyone who is not familiar with the phenomenon, here is a short version of what happens. I wrote a longer article last year. There are more references down below as well.
About ENSO and El Niño
El Niño is one of the phases of the El Niño Southern Oscillation, or ENSO. There are three distinct phases, plus an in-betweener. These are known as:
- El Niño - the phase where the ocean releases warm air to the surface, usually resulting in an increase in global surface temperature
- La Niña - the phase where the ocean cools the surface, usually resulting in a decrease in global surface temperature - though with climate change it usually means a lesser increase, not a decrease
- Neutral - when there is neither an El Niño or a La Niña
- Modoki - which is a part way El Niño. It doesn't affect as much of the Pacific Ocean, and has different teleconnections (ocean-atmosphere links over a distance). You could think of it as an in-betweener that can't make up its mind whether to turn into a full blown event or not. (Don't tell a climate scientist that I said that - they'd correct me.)
- The Walker Circulation, which is a pattern of circulation in the atmosphere, which are called trade winds at the surface.
- Warming and cooling of the ocean surface and sub-surface changes
- Equatorial ocean waves
- straddles the Pacific, sitting around the middle, blowing from east to west with the ocean neither excessively warming or cooling the surface;
- gets stronger, pushing more warm water from the east to the west (where it piles up), and pulling up cold water in the east. This results in a La Niña and a cooling of the surface, or
- dropping back and weakening, sometimes even reversing the circulation pattern, with the warm water that was piled up in the west, spreading back eastward. Because the trade winds (Walker Circulation) are no longer pulling up the cold water in the east, the sea surface in the east gets a lot warmer. The results in an El Niño, and warmer surface temperatures.
|Sea Surface Temperature - 4 to 10 May 2015|
Source: Bureau of Meteorology annotated by HotWhopper
Madden-Julian Oscillation and Kelvin Waves
...the major fluctuation in tropical weather on weekly to monthly timescales. The MJO can be characterised as an eastward moving 'pulse' of cloud and rainfall near the equator that typically recurs every 30 to 60 days.
Pacific Decadal Oscillation and ENSO
|Pacific Decadal Oscillation and GISTemp Global Surface Temperature |
Data Sources: GISS NASA and Nate Mantua
Some further reading
- Flashback to 1910 - the Indian Monsoon and ENSO - an article from the Sydney Morning Herald, back in 1910, on ENSO pioneer Sir Gilbert Walker, after whom the Walker Circulation is named
- Tropical cyclones and ENSO - including how tropical cyclones north and south of the equator may have boosted the chance of an El Nino - March 2014
- El Niño in the tropical Pacific - May 2015
- Gobbling up or Spitting Out Bob Tisdale's ENSO Leftovers at WUWT - a fairly detailed HotWhopper article about ENSO - January 2014
- BoM maintains an El Niño alert - with a basic video from BoM - December 2014
- The Pacific Decadal Oscillation and Australia - plus more - October 2014
- Deniers are weird at WUWT. ENSO is a BoM conspiracy! - November 2014