SAM Trends Positive
Climate projections will have some Australian surfers rejoicing, and others not so
SAM Trends Positive
What if I told you that the last few years provides a glimpse into the future for Australian surfers? One where we live with positive SAM.
No, I'm not talking about an upbeat friend, instead we're discussing the Southern Annular Mode (SAM) - occasionally called the Antarctic Oscillation (AAO).
Regular readers would be aware of SAM, and it's impact to the surf across our wide-ranging country whether in positive or negative mode.
The Tasman Sea looking more like the Southern Ocean (Brokensha)
In layman's terms, it's an index that provides an idea on how far the westerly storm track is from normal. When in a positive mode, the westerly storm track retreats south to polar latitudes and away from Australia, although it strengthens, resulting in higher pressure across the country.
When in a negative mode the westerly storm track pushes further north, bringing more swell to the southern states albeit with associated cold fronts and local wind.
With the recent triple La Niña, lower than normal pressure across northern Australia has resulted in the sub-tropical high pressure belt moving much further south than normal, and in turn pushing the westerly storm track further south towards the South Pole.
This has resulted in a persistent positive SAM mode since 2020. In fact, 2022 equaled the record amount of positive SAM days, which was set in 1998, that being 278/365 (76% of the year).
The impact of a shift in the sub-tropical high and westerly storm track further south is still fresh in most Australian surfers' minds. The East Coast sees more easterly swell action thanks to the movement of the sub-tropical high south, exposing NSW to easterly trade-wind swells, while in the southern states the retraction of the westerly storm track to the south results in smaller swells arriving more from the south, yet more favourable winds for the exposed coasts.
Plotted below is the SAM index for the past forty years, along with a trend line which shows a shift to more positive SAM events during the past few decades.
AAO/SAM observations from 1979-2023. Trend line is shown in red
There are two causes linked to this positive SAM trend, the first being the ozone hole (which is now slowly recovering) and the second being greenhouse gas emissions.
Lets first look at the ozone forcing.
The release of human-made, ozone-depleting chemicals (chlorofluorocarbons etc) into the atmosphere has resulted in the depletion of ozone in the stratosphere since the 1970's. After realising the damage being done, the 1987 Montreal Protocol was introduced, banning the production and emission of these harmful aerosols.
There's a natural cycle of ozone in the stratosphere, with it decreasing through the start of spring thanks to the formation of polar stratospheric clouds. These clouds contain ozone-eating chlorine and bromine compounds, which are released with the arrival of spring time sunlight.
The emission of CFCs added extra chlorine-containing compounds into the atmosphere, hence accelerating the breakdown of ozone, leading to the formation of the ozone hole.
Because ozone absorbs the sun's heat, a lack of ozone leads to a cooling of the stratosphere and intensification of the polar vortex. A stronger polar vortex equals stronger than normal westerly winds around Antarctica - ie a positive SAM mode. This is evident in SAM observations from about the 1970's onwards.
Thanks to the Montreal Protocol we're seeing a slow repairing of the ozone hole and climate models have a weak negative SAM forcing during summer for the coming decades as a result. This is offset by the positive forcing imposed by increasing greenhouse gas emissions.
With the warming atmosphere and warming tropical oceans, we're seeing an expanding of the tropics. This is leading to a more permanent shift in the sub-tropical high southward, ie - positive SAM mode.
We're also seeing a positive feedback loop taking place, where the more that positive SAM events develop, the more we see strong polar westerly winds. These winds promote upwelling of (relatively) warm circumpolar deep water along the Antarctic shelf, leading to ice melt.
The greenhouse forcing is the main contributor to the positive trend seen through winter, and this is the concern for the southern states.
Winter is their prime surf season and any contraction of the westerly storm track - even if it's stronger - equates to a reduction in the number and size of large groundswell events along with less north-west to south-west frontal progressions.
Under this pattern more exposed locations - the Mornington Peninsula for instance - will benefit as winds become lighter and more favourable, but for spots like the Surf Coast, this means a shorter, more sporadic swell season.
On the East Coast we can expect more easterly swell energy as a general rule, owing to a southerly shift and strengthening of the mid-latitude jet, resulting in stronger mid-latitude lows and extratropical cyclones.
Western Australia is a tricky one, with a reduction in strong polar frontal systems in winter likely to be replaced by an increase in mid-latitude lows which aren't of much benefit to the Margaret River region but produce fun surf for more metropolitan locations.
Comments
So what you're saying is I should take up Golf or move East.....?
Thanks for the breakdown Craig.
That lineup shot at the top gets the pulse goin!
just great.
The Tullamarine Tub welcomes the news.
Hmmmm for the short term maybe, but will they be able to hold the attention of poor Victorian surfers long enough? While they sit watching swell after swell batter the QLD & NSW?
Eventually there'll be no surfers left down here!
There will be a renaming of the "Surf Coast".
And that's a bad thing? MP looking good.
Ah jazus, that's not what I wanted to read. Oh well, we will all have to move to the North Coast. Out of interest Craig, what is the vertical scale on your SAM trend line? How "extreme" is the trend?
It looks to be just over 0.5pt positive move in the past 40 years.
Cheers. Do we have earlier data (prior to 1979) for comparison?
It's tricky thanks to the limited observations that make up the SAM index, but there are various reconstructions like below.
More reading here about the tricky nature of reconstructing past SAM modes here:
https://cp.copernicus.org/articles/17/1819/2021/
Cheers Craig. Some holiday reading while I curse Huey for the never ending f***ing south easterlies
An interesting link to comparisons of some reconstructions of the SAM index over the common era:
- paper: Trends and variability in the Southern Annular Mode over the Common Era
- associated slides
The main graphs:
(In this bottom figure over the whole common era, the top graph of the three in the figure has been cut off by me since it's already reproduced by Craig above.)
These papers also seem to link to the main papers discussing the climate science believed to indicate that the recent upward trend in the SAM is due to ozone depletion and greenhouse gases.
Thanks GSCO.
Surf aids for the SC, both QLD and VIC.
Anyone got any CFCs I can borrow?
This has well and truly flattened me. Fuck.
All this positive feedback seems to be causin some serious negatives!
Haha! Wait until the fourth La Nina in a row rolls around.
I’ve been waiting for that Sprout.
Does this correlate with more East / South East winds through the Victorian winter or just less large winter swell events? The easterly wind pattern seems to start earlier and finish later with La Nina, but if this flips to El Nino, do we still get a positive Sam? Basically will we get winter NW winds but smaller swell on the surf coast or no swell and winter SE winds?
ENSO modulates the signal and with El Niño you can expect to see more negative SAM events.
Otherwise, it'd be somewhere in between what you've hypothesised in winter with less large swell events but more favourable winds from the northern quadrant - ie from north-west to north-east.
As a SC surfer, I’ve noticed swells being way more W direction too. Not just the total absence of significant swells. Even my wife noticed the roar of the ocean on the one occasion there was a swell of size this year. It is truely shizen.
Yep agree here 100%.
Whenever we do get swell from that 2-3ft range and up, it’s so inconsistent due to how westerly it always is. Shits me, can be left spending 2 hours in the water for 4-5 waves.
That does not sound too bad? As long as there is at least 2-3 ft of swell and the wind is out of the northern quadrant you'll always get a decent surf on the surf coast as long as you're open to what and where you surf. If we're in for more of that it's a light at the end of the tunnel after 2 months of these endless SE winds! Now what can you do about the state of the MP and PI sand banks?
But the chaff never gets sorted from the chauder. This period alone has bred so many new kooks without consequential waves.
So true. Have you also noticed the pool surfer coming of age? I saw a guy last week it was 2-3 foot, he couldn’t paddle, he couldn’t duck dive. But when he got to his feet he absolutely ripped. My first guess is he is from Melbs and spends a lot of time at the Tullamarine Tub.
Hmmm... so, Craig... how's our snow season this year looking? Warmer with more precipitation?
I was going to ask this as well Brandon.
My interpretation of Craig's analysis is NSW will continue to do well due to its altitude, Vic might be more of a battle as it relies on those more classic SW systems. Hard to say year to year but general trend.
Way to early to say this far out.
So southern coast surfers will want to get to the surf in EVs and have a home ozone generator, while east coast surfers will want to buy V8s...
hahahahahah...
Classic!
Also heard of more southerly direction swells in the SW, Craig does that mean more of those kind of swells which tend to bypass Perth?
The Perth winter just gone was pretty avg due to the lack of frontal activity, mainly mid-latitude cut-off lows. The mid-lat lows just don't cut it as they don't move the sand around, hence the shit summer banks hang around longer. They also bought more rain and wind to up North.
If you listen to one long time Perth surfer/shaper who surfs everything and froths on closeouts the winter was like getting a hummer off Julia Roberts (look her up kids), i.e. exceptional. Jeez she could suck a tennis ball through a garden hose with that gob.
I think I know the surfer/shaper you mean, he's a legend. I'd be a grom in to see him and he'd be "Yeah I went down south for the weekend, yeah, Bears, 350 waves..." and I'd just blink.
Was around a little bit over the winter and it was good - saw one bloke get a stand up barrel off takeoff at Hale Rd, got a few good ones myself but he had the stars align that day. Shallow on the bank!
So it means mean more southern swells in Indonesia?
In general yes, the ones with the period and strength.
all is not lost for us mexcians south of the boarder yes....this is ok for east of melbourne. and its summer forcast not winter:)
Yes, wind and smaller days has helped east coast beachies but the banks east of Melb seem to have been consistently more shitty the last few years.
I wonder if the lack of bigger swells has thwarted the usual cycle of sand movement?
doesnt big swell destroy sand banks. ie small swells for 2 months and there should be good banks on open beaches....happy to be corrected.
Yes there is sand but there aren’t any rips to give it shape.
Eg First carpark is basically a 500m close out when there are usually at least one or two rips creating a rideable wave.
Maybe bigger swells are needed to create these..
big swells just create gutters i thought. i got told by an old torquay local a long time ago that for examlpe, that you could have multiple gutters out to the ocean if there were lets say 4 big swells in a month each bigger than the last. its just natures way of protecting its self. ( the actual beach itself). and i did used to think big swells would make good banks beacuse rips would form and you would have left and rights. but big swells in vic just buldoze the surf zone. and happy to be corrected on that.
Peninsula beaches often seem to benefit from a flush out from a bigger swell. Can take a bit of time to resettle afterwards but eventually something happens. The banks have been pretty stable for months over summer but many are starting to break down and need a to restructure. Consistent easterly/se wind pattern hasn't really helped.
In general, big swells create the v shaped rip banks especially if it is high energy with lots of water moving about. A well-spaced deep groundswell may not so much. But it depends on the beach set up, swell direction, tide cycle at the time and other X factors.
A beach like Woolamai, for example, tends to form banks in the same general spot due to prevailing swell directions and water flows. If, however, a big swell comes in from an unusual direction it might be trying to shift the bank / rip patterns slightly and be trying to "go against the grain" producing a rip where a bank is usually. This can stuff up the banks or create something surfable but unusual.
Once banks are in place in the "right" spot for a particular beach, it creates a much more stable set up for staying good for a long time. If subsequent swells support the existing placement they can groom and maintain the bank. More random swells might fill in the channels or cut into a nice line of sand creating dead spots.
One good swell can set up banks for months. Another sizeable swell from a slightly different angle can blow them apart.
In Victoria, a good swell season should mean good banks between the main swell events. Shitty swell seasons would be not so good. But in the end, it is too complicated to forecast. More a case of when they go bad, they may well stay bad for some time.
Some long time locals may have it figured out. However, in practice they just benefit from being there at the right time or tide rather than any longer term prediction skill.
Makes alot of sense. It appears perhaps then that we have had the benefit of smaller swells to allow banks to gather sand but the lack of a few decent ones to wash through and dig out some good gutters.
I read it to affect all year not just summer
The ozone forcing is greatest in summer, where as GHG forcing is year around but most noticeable into winter.
Imma likin this
“ The release of human-made, ozone-depleting chemicals (chlorofluorocarbons etc) into the atmosphere has resulted in the depletion of ozone in the stratosphere since the 1970's. After realising the damage being done, the 1987 Montreal Protocol was introduced, banning the production and emission of these harmful aerosols.”
Craig how does a large volcano eruption into the atmosphere compare with man-made greenhouse gas emissions.
Eg - can you say one eruption is the equivalent of 5 years of man-made emissions? This is just an example obviously.
When you can stop a volcano, let us know...
It took 10 years for industry to stop CFC's in fridges and air con's f'ing the planet......
"Unfortunately, the chemical stability of CFCs turned out to be a problem that threatened the whole world, as scientists discovered in the 1980s. Leaking CFCs, mostly from discarded equipment, remain in the atmosphere for a long time. Eventually they make their way to the stratosphere, where they are finally destroyed by UV radiation from the sun. But when they break down, they create chlorine that reacts with the protective ozone, letting dangerous radiation through to the Earth's surface."
"When production of CFCs was eliminated in the 1990s to protect the ozone layer, new refrigerants were developed and the industry shifted to HFCs......"
"HFCs are like CFCs but much more reactive in air, so they never reach the stratosphere where they could harm Earth's protective radiation shield. They largely saved the world from impending ozone disaster, and they are now found in refrigerators and heat pumps everywhere."
"But while HFCs' chemical reactivity prevents them from depleting the ozone layer, their molecular structure allows them to absorb a lot of thermal radiation, making them a greenhouse gas. Like carbon dioxide on steroids, HFCs are extremely good at capturing infrared photons emitted by the Earth. Some of this radiant energy warms the climate."
Reference: https://phys.org/news/2022-09-climate-hfcs-refrigerators-air-conditioner...
"Human activities emit 60 or more times the amount of carbon dioxide released by volcanoes each year. Large, violent eruptions may match the rate of human emissions for the few hours that they last, but they are too rare and fleeting to rival humanity’s annual emissions."
Reference
https://www.climate.gov/news-features/climate-qa/which-emits-more-carbon...
George Orwells' 1949 book "1984"....possibly predicted a feedback loop of ignorance managed by P.R.
" the novel examines the role of truth and facts within societies and the ways in which they can be manipulated. "
https://en.wikipedia.org/wiki/Nineteen_Eighty-Four
"1984" free Ebook
https://gutenberg.net.au/ebooks01/0100021.txt
Thanks, this is along the lines of what I was wondering.
Thanks Bbbird, the recent Tongan eruption was equivalent to that of Krakatoa in 1883 and we'll continue to see the flow on effects of this over the coming years.
It also helped create a significant ozone hole last year due to the mass injection of water vapour high into the atmosphere.
Thanks Craig, it seems strange to me, although not a climatologist, that 1998 (a huge El nino year) had the effect it did on SAM, as per your quote below, maybe I am missing something? Thanks for any enlightenment:
'With the recent triple La Niña, lower than normal pressure across northern Australia has resulted in the sub-tropical high pressure belt moving much further south than normal, and in turn pushing the westerly storm track further south towards the South Pole. This has resulted in a persistent positive SAM mode since 2020. In fact, 2022 equaled the record amount of positive SAM days, which was set in 1998, that being 278/365 (76% of the year).'
I thought the same but looked into it closer and 1998 saw a rapid transition from strong El Niño to strong La Niña. I'll get the data for you.
Here ya go, here's 1998..
Thanks Craig, if the X axis in the 1998 plot is time (?), then it seems that SAM was already mostly positive prior to May? Does 1997 shine any additional light on this? The inter-relations among all these different climate forcings (El Nino - La nina, Indian O. Dipole, Pacific Decadal Oscillation, Jet stream shifts and all the extra heat in atmosphere and oceans, etc.) are obv. complex and well above my pay grade, but like most readers I greatly enjoy your articles and their relevance to waves and winds! Cheers.
Yeah it was, 1997 shows a strong negative dip (down to -4.8) into the final third of the year as the El Niño really kicked into gear.
Might have to pull up some other charts to see how the Niño to Niña switch played out when I get some spare time.
Thanks for that - fascinating stuff.
Actually I'm going to bet on extremes reverting and a negative SAM and no La Nina, and pumping southern oceans because big volcano, but mostly jus' because...
Must have been a bumper SC surf season in 2002!
Positive Sam,
Why do cheerful people annoy me?
There's just something about bright and shiny people that annoys others. Turns out, the vexation is not completely irrational. One thing cheerful people don't have going for them is optic management. Research shows people who are unfailingly happy are perceived as naive and gullible.8 Jan 2022
https://theswaddle.com › the-science...
The Science Behind Why We Find Perky, Happy People Unbearable.
I think I only like positive Sam when he gets depressed and turns negative.
These westerly swells and SE winds have left Vic with sand in all the wrong places.
Hopefully we back out the way we came into La Nina and the beaches light up.
Thanks Craig, masterful article
The other thing that's positive about this article is the fact that we came together globally and acted, on the advice of the scientific community, regarding the man made hole in the ozone layer and it seems we fixed it !!!
Now if we could do the same in relation to our CO2 emissions would that then moderate our nasty SAM trend line?
Save the climate, save the surf coast.
(Not sure how well the Great Ocean road will fare in the near future if we are suddenly hit with large swells).
Hi Craig, saw this today:
https://www.abc.net.au/news/2023-01-18/la-nina-weakens-el-nino-weather-p...
I was in Sumatra most of 11/22 - got skunked the whole time; NW winds, no SW swells of significance, owner of accom's said it had been raining non-stop since 08/22; adding "the worst peak season in 17 years" etc.
Licking my chops from that non-surf trip, I'm thinking of going back to Indo in April; so as not to blame nature and fill my empty wave bank - but I read your story above and this ABC link; and think, from my limited technical perspective, it all reads to me like if I went back to Indo in April I'd be getting skunked again?
(I prefer the cross-seasons due to lower crowds)
Thoughts?
Bummer!
La Niña isn't giving up yet, but I'm still confident it'll dissipate over the coming months, even with another burst of easterly trades forecast over the coming week. We'll continue to watch this space.
Over in the Indian Ocean it looks like we'll see a resumption of normal programming and weaker trades through that period.
The Indian Ocean Dipole really effects things through spring and not in the lead up.
Craig > good man; thanks for the update. I'll ask again at end of feb - see where you're at with global data - as I don't want to blow another $3k. > RR
Craig does this have much affect on Fiji?
Got a mid-year trip in the pipeline
The SAM stuff?
In general with less frontal activity pushing up and across the southern states, onwards through the Tasman Sea you'll be relying on more distant polar swells, which coming from that area is favourable for reaching Fiji.
So less large swells and a mix of quality long-period stuff with mid-period swell a possibility from Tasman Lows. Lots of factors come into play for Fiji.
Cheers Craig. Yep the sam stuff.
i thought Indo last year was inconsistent surf, and wind wise.
More east swell and cyclone swell for the east coast isnt a fair trade for SE groundswell in my book
Yep, thanks to the La Niña signal and - IOD event. We saw mid-latitude lows and fronts which produce smaller, weaker, lower period swells along with those funky winds.
Craig what was the set up for the 10 year drought we had from 2000 then?
Qld surfers may need to consider what comes with the warmer water currents flowing south atm....
http://oceancurrent.imos.org.au/sst.php?regiontype=1
http://oceancurrent.imos.org.au/product.php
"saltwater crocodile sighting on North Stradbroke Island"
https://www.abc.net.au/news/2023-01-18/parks-and-wildlife-investigating-...
Large Black bubble is where both models have the aao now and there forecast, aka sam. Colors are where it may trend to in the future.
Is it known what caused the spike in positive storm tracks in the 1100s and 1200s that’s shown in the reconstructed graphs?.
This was the Medieval Warm Period, and it looks like there were indications of a mostly La Niña like setup..
"There is an extreme scarcity of data from Australia for both the MWP (Medieval Warm Period) and the LIA (Little Ice Age). However, evidence from wave-built shingle terraces for a permanently-full Lake Eyre during the 9th and the 10th centuries is consistent with a La Niña-like configuration, but the data are insufficient to show how lake levels varied from year to year or what climatic conditions elsewhere in Australia were like."
This also correlates with drought in North America and also coral observations indicating a La Niña state.
Sam forecasted to dip at the end of the month. Correlates to the next incoming mjo. Teleconections.
AAO aka Sam is forecasted to trend into + again later this month.
Sorry Craig if someone asked this already - can't see they have...will the + SAM result in decreased rain for the SW of Australia?
Yeah it does because moisture laden fronts are suppressed and you get drier, east to south-easterly winds.