Submitted by sarge4 on Tue, 02/11/2014 - 10:00
Its been mentioned on a few internet pages El Nino conditions may be forming in the Pacific. Does anyone have any opinions/information/experience on how El Nino effects swell activity in the Indian ocean? Does it effect swell size, frequency, timing etc?
This is a topic I'd love to spend some time researching in detail, as (to the best of my knowledge) I don't think anyone has ever undertaken a detailed study on the relationship between seasonal surf trends and long term atmospheric/SST oscillations.
Thanks for the reply Ben. Surely there is a PHD in this for someone!
Do you have a gut feel? A mate of mine reckons El Nino = excellent early season indo.....
Well, first we have to define what constitutes an "excellent early season in Indo".
As for my gut feel - no, I don't have one. I don't like speculating on this kind of thing until I've seen some hard data (and.. which coastlines would we be looking at? This is another important part of the discussion).
My mate lives in Bali and i think the "excellent early season in Indo" reference is about more consistent S-SSW swells during the Feb, March and April months. Myself l'm just interested if there is a corrolation between the development of El Nino and activity in the Southern Indian and any impact on the trades. I guess i'd been thinking about last year when the trades we're late to really kickin, it rained well into the season and also the exceptional run of later season swells. The trades also seemed to hang in a bit long last year.....
And that's the crux of the problem.
We can essentially split this into two studies - the effects of Phenomena A on swell prospects for the region (which has its own variables - size, period, direction, duration etc), as well as the effects of Phenomena A on winds and weather for the region.
Because, even if we found (for example) a strong correlation with swell prospects, it ain't much use if local winds and weather are terrible.
That being said, it's a fascinating topic absolutely worthy of a PhD which I hope to spend some time researching at some point in the future.
Going by pure local surface conditions ( ie the ENSO -IOD influence ) which in unison provide the timing and strength of the Monsoon on Indo and Nth/Nth West Aust .
2012/13 Sth Hem wet , was late to start and the when it did it was solid but long lasting . ( ie the warm anomaly waters asociated with a late Negative IOD where not dissapated Quickly and hence it took longer for this Energy / and local wind efefcts to diappate . Hence the late start ...
This year however again we had a neutral to late surge in IOD to negative but not maintained . The wet has been late , but with back to back MJO Passes with a complete retrograde of teh Monsoon we have seen a large portion of the energy dissipated without many large Cyclones . SO there could be some credit in it possibly being an early start to trades or even a quicker transfer to variables for Eastern coasts or eastern Indo . Obviously the Enso will have effect of the mid lattitude highs which will give light winds for swell to pass through and less chance of that energy being tranfered to a more Sth SE direction and make the strongest parts of the swells concentrate on Western Archipelago .
However the " engine room " is more complex issue where the Southern Indian - Southern Ocean and location/ source of Frontal systems compacting or bombing is more to do with the
ACW , Antarctic Circumpolar Wave [ sea surface temp. ] , ( which is a dual nodal warm anomaly ) of surface waters within the ACC Antarctic Circumpolar current [ sea surface / slightly subsurface ocean gyre ] . Although the general flow of the current is west to east the ACW actually lags it in and will take roughly seven years to complete a cycle .
Where these two mean anomalously warm nodes sit in a winter season will influence the LWT Long Wave Trough ( Atmospheric ) immensly , and thats why often the late season and early season differentuate so much on swell directions , and if timing is ill the wave node is too east under Aust or too west under Africa either early or late season . This is when you will see an inconsistant or short lived season for swell action ....
As Ben has noted , they are seperate but loosely linked , and there is more influences too complex to even contemplate ...... ( for now )
PS ... ENSO stands for El Nino -Southern Oscillation
and IOD stands for Indian Ocean Dipole
" SA's Reserve Capacity "
Regarding state of ENSO... https://www.facebook.com/JohnsWeatherChannelJwc thinks that the BoM might be the best ENSO forecast model atm, which isn't leaning so hard towards El Nino. Reason being the other models have been changing towards POAMA (BoM) relatively drastically, which may be an artefact of the decreased sampling of the ocean. My impression from weather nerds on the web is that things are, and will remain neutral indefinitely....
Yes Mitch ...
The Aussie model , POAMA II ( the first was really shit , and i beleive Dr Andrew Watkins amongst others produced the second version partially in response to nerds including myself bagging BOM and the original POAMA model out publicly on WZ ) , it seems to be doing better of late .and more so when in comparison to others ... And i think it is more OZ centric to its readings as i beleive they have more input into it than merely sea surface / subsurface and atmospheric . BOM look at cloudiness and OLR amongst many other things , and have for a long time but perhaps they have finally got all their inputs correct for the Model to operate reasonably accurate .... Of note nearly all other models have been forecasting El Nino for nearly the past 4 years in a row ....... ;-)
Btw, I have it stuck in my head that the higher levels control the lower levels, so how do SSTs control the jet?
The easiest explanation is to Google " Walker circulation " or Hadley Cell .
Generally most literature covers the well known Equatorial patterns ....
However we are talking a 3D system , so its hard to see the Lattitudal mixing .....
but its there .... Remember that an Upper Low will help a Surface low ( low pressure = equals lifted air mass ) to draw even further upwards , and faster = increasing the coriolis effect ...
Which inturn will help a surface low Bomb = drop central pressure rapidly as the spiralling airmass has lower pressures or rising air mass above ...
Pls keep in mind that i haven't been taught this , so perhaps Craig and Ben may explain it more accurately and concisely ..... although they probably don't want to do themselves out of a job either . !? Ontop of old salty dogs wanting to lynch me for sharing too much acquired knowledge . But you did ask , so i felt obliged .;-)
Ok, that gives the general framework.
But to what extent does that rising airmass control the velocity of upper level winds, vs the rising airmass just takes a path (upwards) of least resistance (shear against the jet stream)?
I wonder how that relationship changes with changes in the properties of the air masses (e.g: you mentioned what seems to be a positive feedback loop)...but it's too much for me atm
I imagine a wrestler (the surface low) being bounced off the ropes (the jet). The more energy put in (higher SSTs) the more he can bend the ropes (direct the jet), but he'll (almost) never go through them... sound alright?
So one possible scenario might be...
La Nina -> increased in rate of circulation of the Pacific Gyre -> inc. ACC circulation -> lower chance of extended flat spells???
P.S. I think formal education can easily put people into a rut of fact acquisition and not necessarily learn anything. Whereas self education really is self driven, it's just it's harder to self check against something/someone.
Would anyone agree that the Indian Ocean is actually a very consistent cyclone producer? As in cyclones per month per sq. km. as a measure of cyclone activity.
This is based on my casual observations of ASCAT over the last 9 months...
Ok according to wiki it's not haha... but I guess it doesn't take surface area into accounthttp://en.wikipedia.org/wiki/Tropical_cyclone_basins#North_Indian_Ocean
Yeah norwest oz gets lots of em . More than eastside maybe? Theres waves up there ...
Yeah norwest oz gets lots of em . More than eastside maybe? Theres waves up there ... Looking at that link does that mean 2nd most amount of cyclones?
Mitch vg - only study I can find is by a "cj Newman", 1993; Cyclones per year -
Nth indian - average cyclones/hurricanes with winds above 63kmh - 5.4. Severe cylcones winds above 120kmh - 2.5
Sw Indian - average cyclones - 10.4, Severe - 4.4
Se Indian (Australia) - average cyclones - 6.9, Severe - 3.4
Interesting page on dipole - http://weathergaines.blogspot.com.au/2010/02/indian-ocean-dipole-el-nino...
Having never spent the majority of my surfing life in Qld ( and only the past few years in applevania), all I know is El Nino sux..........
Correction "Having spent", not having "never" spent.....
mitchvg wrote: P.S. I think formal education can easily put people into a rut of fact acquisition and not necessarily learn anything. Whereas self education really is self driven, it's just it's harder to self check against something/someone.
Apologies Mitch i didn't see this . and i rarely check my emails . especially when there is waves or i need to smash work to make time to get wet .
The Paciifc Gyre is one portion of other influences on the ACC . Obviously with such length of Equatorial waters the Pacific is the biggest " feedback mechanism " of the Ocean to atmosphere connection . And its got many pole ward returns in both Atmosphere and oceanic gyre flow . One of which is into the Indian through the ITF . As i mentioned its complex , and such the entire system is seriously misunderstood / or lacking in real time knowledge , there are patterns but the overlaps and influnces border on chaos theory . Its best you just learn to know the small parts that your interested in rather than the whole shabang ... Patterns and seeing them is the important part here in places you have interest in knowing .
As for the uppers , they still operate on similar principles as the surface , except you are starting to get into thicknesses ( vertical columns of shared pressure ) , obviously due to the vertical sheer component winds and pressure gradients can be far more severe . Generally the Jet stream is the upper winds counter flows to the lower coupled surface pressure cells .
Getting back to the ACC ( southern Hem. ) its influence on the Jet is harder to explain and i struggle with just words ( and due to lack of time , enough imagery to link to ) WZ does have a weather glossary on its forum . Theres plenty of other literature out there ... it does get boring , and makes you question the outlay to reward ...
The easiest way to " try " to explain it is that warmer regions within this two nodal " wave " of SST's forming the ACW helps the propogation?? / formation - strength of surface lows as naturally the atmopshere directly above these broad regions of above mean SST's are lifted to start with as warmer air rises , of which over a large scale increases hadley cell " averages " . So generally speaking those areas will see upper lows , more easily anchor ( stall / hang around ) . So with this influence as a Passing Surface low in conjunction with the circulating and " pulsating = equatorialward stretch " of the moving LWT ( upper low pressure belt ) .... The longer an upper low stays over or interacts with the surface low the more they will BOMB .....
LOST ??? apologies .. i tried .
No, copy that Southey.
[quote=mitchvg The longer an upper low stays over or interacts with the surface low the more they will BOMB .....
That makes sense too me Southy, they all have to line up vertically yeah,,,,?
That makes sense too me Southy, they all have to line up vertically yeah,,,,?
Our brains are too small at the moment to comprehend the reality of what's happening in our forests . We're only just waking up so to speak . The big problem is we think we know everything, we are specks of dust on a timeline and we know nothing .
Ted Bryant (who is was a climate lecture at U o Wollongong back in the 90's, and also an expert in tsunami ) reckoned there was a correlation between La Nina events and the formation of east coast lows. Based on my observations as a surfer I reckon he is right. However major swell events which have resulted in massive beach erosion on the east coast have corresponded to the strong El Ninos of 73 - 74 (?) and 82-83 (I could be slightly off with the years as my time at uni was punctuated with some serious brain cell destruction).
Ted also alerted me to the reason why my local (and many others) would end up freezing cold in the middle of summer after a howling noreaster. Eckman Transport. Look it up if your beach is afflicted with this mid-simmer menace.
That would be 100% correct tgi , if 73-74 were El Nino dominated periods ..... but infact High on the scale of back to back La Nina's and strong too ( on the atmospheric side of things ) .... But interestingly i think that a Negative IOD may have also setup or helped kick start atleast one of those years ?
Welly , divergence above helps draw up or more to the point NOT create a barrier to the surface low " exhausting or continuing to spiral lift .
Speaking of Spiral , The Ekman transport is also referred to as Ekman Spiral ..... The ocean can at act very similar to the atmosphere and their influence on each other is definitely a two way street . Its just
that apart from land interaction making short term changes involved in sea breezes and Upwelling , generally speaking the oceanic changes are far slower .
Next week we will cover Kelvin waves ;-) ..... just kidding .
Is an upper low created by *whispers* uplift of a surface low? And are they the same air mass?
Caml - ah yeah of course NW OZ does, only just realised that it is in the Australian Area of Responsibilty. So that figure for activity does not include the entire Indian.
sheepdog - cheeers. That's interesting as I've paid particular attention to how the Bay of Bengal seems to capture cells. So I thought it would've had more. It'll take me a while to get my bearings on that site though :/ I'm a bit scared of delving into the dipole.
Southey i wish i could understand your lingo . Ive just learnt of ekman spiral , thanks . Got a question will swell form easier from wind and the earths rotating in sync , say from a cyclone compared with westwind trades swell ? Southern hemi for this example . The earth spins eastward and that drives the ocesn currents , can it help swell propagate ?
Haven't had a chance to read all the above comments yet, but re swell forming easier from wind travelling with the rotation of the Earth instead of away with it.. you're a big thinker Camel, and I like it.
But... there is nothing in this unfortunately.
It's all about relativity and I think you're forgetting that the storm itself is actually moving, along with the ocean in sync with the Earth, carrying the same momentum.
Sure if the Earth and ocean was moving while the storm above remained stationary relative to the Earth you'd see your ideas bearing fruit, but this isn't the case and the closest thing to this actually occurring is a 'captured fetch' scenario. Where the storm moves at a similar speed and in the same direction to the swell it is creating, resulting in the sea state growing much faster and the swell becoming bigger than under normal circumstances.
Also remember if we didn't have the Earth's rotation we wouldn't have the Coriolis Force and in effect, no spinning storms.
Craig, on a semi related topic, an old sea dog on an even old prawn trawler told me something back in the days of telegrams, neil young and buddha sticks.... Sorta stuck with me.... Wanna know if it is true, and if there is a terminology....
In laymans terms, he said that when you have a direct long period south swell (or direct north swell) travelling through a relatively calm patch of sea, the earths rotation will very slightly bend the swell westward. He said it's only a matter of a few degrees. I've sorta taken this on board all my surfing life. I've seen cases where it seems like this has happened. Am I living a lie? :) If true, what is the scientific name?
Will get back to you on this soon.
What Craig said ....
Only " Upper lows " will have a tendency to be lagging on the earth rotation , due to "drag" ( for want of a better term ) from the stratopause .
Again , these guys are far better at this stuff ....
One thing is for certain , and its been discussed here in the past , unless a Cyclone drops down into a fetch of accompanied in state " trade swell " , then it will struggle to get much output in the way of swell , unless of course it can achieve a captured fetch , but rotating / spinning whilst retro grading ( westward movement / against earths rotational pull ) for atleast a few hundred km's .
Transitioning systems , ie like what energised the southern ocean westerly swell machine last week is far more likely , and is very similar to what happens in the NW PAC , and Nth Atlantic every Boreal winter .
the only thing i know at the moment is that we are more than likely to go into a medium strength Winter / Spring El Nino .Peaking before this time next year then Followed by another STRONG La Nina in 2015/16 .
BTW the ocean currents aren't directly driven the earths rotation , far less emphasis is placed on the mid lattitudes westerly wind belts that are the motor of these currents , they themselves are driven by the coriolis effect , Everthing else is either a return path or a thermal mixing reaction .
Getting back to you Sheepdog on the Coriolis Effect on swells.
And in short the answer is yes (but for any swell direction and the sea state/conditions don't matter).
Now, the Coriolis Effect only starts to influence any moving object on a spinning surface if the time in which it is travelling is at least half that of the time it takes to complete 1 revolution of that spinning surface.
So with the Earth, it takes 1 day to rotate, so any object that moves for a period of 12 hours or more will see the Coriolis Effect kicking in. Deflecting to the left in the Southern Hemisphere and to the right in the Northern Hemisphere.
So this applies to swells as they travel and exist for well over 12 hours but is also taken into account and calculated by the wave models. It's if you did these calculations manually that you'd have to take it into consideration.
This also disproves the water down a toilet bowl myth re spinning one way in the Northern Hemisphere and another in the Southern Hemisphere.
This can't be possible as the water would have to take over 12hrs to go down the bowl instead of seconds. The spinning is just relative to the bowl shape and where the water is injected.
Also the Coriolis Effect is also the reason we see upwelling across certain regions as explained here: Why does the water get cooler in Sydney after a nor-easter
hey craig ,thanks but cant quite understand that . do you say that its true or not ?
Just edited a little. Yes it's true.
okay thought so .sheepdogg knows a few tricks .
greater circle path , swells moving through trade winds will enhance this .
Super El Nino prediction for the coming year.
Just Super ..
High chance of El Niño and Perhaps strong , but most likely not SUPER ....
Jamstec ( arguably the most accurate agency ) , have this possible niño peaking
Early , and then a high chance strong Nina to follow ..... The following
36 mths .
I can't bring myself to read through such articles. "super el nino"... i know what their point is straight away, so why bother reading? It's so frustrating to see this be such a divisive and narrow minded issue.
But, I find it curios that the SOI has dropped so much, although I haven't been following it day to day. I would've thought with cyclones just E and W of Darwin recently, the SOI couldn't have dropped that much, even if there has been cyclones in the central pac as well???
Southey et al, can any of you guys point me in the direction of where I may be able to find historical IOD readings, dating all the way back to 1997 (did they even log the IOD back then?)?
It's a start...
I've found this which has some data going further back but it would be good to actually see the raw data/specific dates better.
Question I have is the IOD Mode Index different to the IOD Index as the figures on the JAMSEC wesbite are different to those shown on the BOM link above?
ie 1.4 Jamsec reading in Sept 2012 vs 0.8 BOM reading in Sept 2012?
I think I found it.
sorry don ,
been busy " discussing " things eleswhere . will find something easier / The actual figures ( as far as i'm aware aren't as important as the ENSO . ENSO's oceanic influence ( for australia anyway ) is measured as a cross reference of two areas . the Regions are shown on BOM but from west to east ( all on the Equator ) you have 4- 1 ..... Regions 3 and 4 are cross rfeerrenced or averaged and placed as a figure of anomalie from normal or average .
Whilst the IOD is from completely opposite ( polar) and E-W regions / sides of the Indian ocean .
And are subtracted / or the difference measured from each other much like the atmospheric component of ENSO being the Southern Osciallation Index (SOI) ..
I know you probably know this , but what i'm getting at is like the SOI its influence isn't squarely on the strength of it . And even less so the IOD . Many guys including myself like to look at longer accumulative totals in the SOI to see where we are in a cycle .
So having that in mind BOM have a chart ( and don't ask me how they have extrapolated it ) that simplifys the categoration both and defines them either warm/cold and wet dry ... When i had more time i started and didn't finish my own amplitude , frequency and tendency of both ....
I'll finish one day . But untill then i'll find the BOM? or csiro one , and post a link .
southey wrote: its influence isn't squarely on the strength of it . And even less so the IOD .
e.g. when the SOI is -8, the influence will be different if it's transitioning from La Nina to El Nino vs El Nino to La Nina?
yes , but it depends on which way , how fast etc etc ... also if you add up the average monthly totals you get a long term trend which some say can correlate to the PDO / IPO influence / long term cycles ....
Don , try this
Thanks Southey. Can I ask where you got that table from? It's odd that there's only been one year of positive IOD and La Niña which is very different information to what I've found?
Although I am only looking at a specific month in each year but still.
Don , I'll have to do some serious homework to find its source . But my source most likely got it form Bob Tisdale .
Generally speaking if a true La Nina is phase , then most likely the ITF transport pretty much will negate a Positive IOD . The only chink in that theory is that the SAM , ACW or Sub tropical IOD (can't remember the true acronym ) , causes an atmospheric anom , that drives the western zone higher than the Eastern ( sumatera ) zone ......
IOD measurements are not as advanced as ENSO ...... most likely if and when India get more spare cash to throw at things like advanced weather bureau funding will it be understood as finite . Untill 5 years ago , wheat farmers in the NW of VIC were the most knowlegable of the IOD or atleast its affects on SE Aust precip. patterns ....
BTW , someone maybe sarge4 was asking of early season , well by my limited observation it looks ripe for INDO .
Been a very quiet early season Indo thus far Southey.
My prediction? Now this is a hail mary....... A large El nino is on our doorstep..... The last two tropical low have formed in what I call the "el nino corridor"......... It's not a good sign for inland Qld farmers, and cyclone swell devotees...... I hope I am wrong.....
It's well underway bloke. Just a question now of how strong and when it peaks.
Yeah, no Hail Mary when the BOM are also on board...http://www.bom.gov.au/climate/enso/