El Nino hangover makes waves
We're now six months on from one of the strongest El Nino events in recent history and a quick glance at current Pacific Ocean sea surface temperatures paints an amazing picture.
During El Nino the easterly trade winds weaken across the equatorial Pacific Ocean and sometime even reverse. This results in warm water 'piling up' through the central and eastern Pacific Ocean (see image 1).
Image 1
Once the El Nino starts to weaken - as it is right now - we get a rebound effect where the easterly trade winds re-intensify across the equator. The result is the pool of warm water shifts, while cooler water from below takes its place. The cold water then forms large, wave-like eddies spinning off north and south of the equator (see image 2). Some of those 'waves' extend many hundreds of kilometres across the ocean.
Image 2
Is this normal and are those wave patterns real?
The quick answer is yes.
In the past we've spoken about Ekman Transport where surface water moves at 90° to the wind blowing over the water. In the southern hemisphere (SH) the water moves 90° to the left, in the northern hemisphere (NH) 90° to the right. We can then visualise that suface waters will diverge right on the equator leaving space for the cold water to upwell from below.
Image coutresy of Sonoma State University
But where do the wave patterns come from?
Well, remembering that easterly trade winds produce a 'transport' of surface water to the left in the SH and right in the NH we can see how this colder upwelled water is curved into a wave like pattern each side of the equator, spawning off into oceanic eddies (whirlpools).
These eddies will move away from the equator and slowly break down over time, helping to distribute the colder upwelled water throughout the Pacific Ocean.//CRAIG BROKENSHA
Comments
Love this stuff. Thanks again Swellnet for providing quality useful content in amongst the mountain of shit I get on my facebook etc. daily from the majority.
Agreed.
rarely comment on it but I love this sort of stuff.
Thanks guys, I love discovering and putting together these pieces just as much!
Yep. If would be great to have a weekly edition of this stuff.
I wonder if in the bottom picture, the inspiration for billasbong logo came from ;)
So does anyone believe we are heading for an la-nina? The Bom is at 50% each way bet. Who want's to go out on a limb?
This is awesome. Thanks for the info!
Nice Craig. Regarding whether a la nina will follow, I think the last two big el ninos were followed by strong la ninas, but Craig would know where to look for that sort of information. But as in financial investments, past performance is no guarantee of future returns.
It was a very interesting el nino for Australia, not bringing the normally continent wide dry. Indian Ocean dipole is also a major influence, and if memory serves me, this was initially looking bad but then switched around, so the drying effects weren't as bad as previous events.
Having said that, yes, some locales were drier than normal for some periods. Overall, rainfall was pretty good for such a strong event, but over the whole country there were many spots that still received good rains, and Australia's east coast dams are pretty full.
Warragamba is at 98% at the moment.
Strange days indeed. Some really interesting weather patterns this year.
Inviting Freeride to tell me that it was bone dry up his way for a stretch.
People wanting more info , or even just follow what some amateur experts and professionals alike breaking down the data and potential outcomes . Weatherzone has a Forum thread dedicated to ENSO -IOD and other Australian centric climate drivers .
As for sticking ones neck out , I'm reasonably confident of some sort of La Niña or cool neutral this summer . But more important to my musings is the insanely strong Negative IOD now running and the possibility of the PDO switching back to negative .
If that happens in the next few months then it's all bets off and start building an Ark .
This video and the following are pretty good at explaining the potentially wet spring.
http://www.bom.gov.au/climate/iod/
"Last week’s index value, −1.37 °C, was the most negative value of the index in at least the past 15 years."
Useful information.
Thanks Willliam and Southey.
Don't worry, I think Russel Crowe has built an ark ready to go. You just go to get up to Coffs Harbour before the floods.
El Nino is back!
Looking foward to another Craig analyis and piece on what the ramifications of this El Nino period will be.