Sudden Stratospheric Warming update
Three months since the Sudden Stratospheric Warming (SSW) event over Antarctica, the verdict is out on its effects on the weather and also surf across the Australian region.
This event was only the second in recorded history (since the phenomena was identified in 1979) with the last event occurring in 2002.
With the 2002 event being the baseline, the Bureau of Meteorology nailed the outlook following this SSW event in early September, that being the forecast of strong negative Southern Annular Mode (SAM) events in the months following.
There's a lot of acronyms flying around above, so here's a brief summary of what's occurred.
The forcing and development of such a rare SSW event is still being discussed, but the very strong positive Indian Ocean Dipole event and cold waters off Indonesia have likely played a part in disturbing the atmosphere (setting up a blocking pattern), and this disturbance propagated from the lower atmosphere (troposphere) up into the upper atmosphere (stratosphere). Additional mountain forcing from the South American Andes looks to also have played a part in setting off the initial disturbance.
This disturbance caused a sinking of cold air in the upper stratosphere, and with all things being equal, a significant warming event occurred, jumping around 75 degrees, hence the term – Sudden Stratospheric Warming.
Such SSW events then disrupt the polar vortex (strong westerlies sitting around the south pole) even causing a reversal which then propagates slowly back down into the lower atmosphere. It took a good while for the SSW event to properly start influencing the surface weather, with it filtering down just over a month after the event.
What this has resulted in is instability in the surface westerlies and zonal flow (west to east) in the form of negative Southern Annular Mode (SAM) events.
Regular readers of Swellnet would be familiar with the SAM, that being under positive SAM events, the westerly storm track retracts closer towards Antarctica, while under negative SAM events the westerly storm track is shifted north towards Australia.
In 2002 strong negative SAM events were seen in the wake of the SSW event, and this year we've seen the same.
The south-east corner of the country has been copping persistent cold fronts, cooler weather and plenty of surf, not typical for this time of year where smaller swells and more favourable winds from the eastern quadrant are usually the norm. Victoria's Surf Coast has offered numerous days of great waves, while there have been some standout days across the South Australian coast closer to Adelaide when November usually goes flat.
December snow. Image courtesy of Hotham Alpine Resort
The colder air has also provided numerous out-of-season snow dumps to the Victorian and New South Wales high country, but on the other side of the coin, these unusual westerly winds have fuelled and played a big part in this years unprecedented fire season on the East Coast. Instead of moist onshore easterly winds, dry, hot westerly winds have intensified any small fire outbreak.
Monthly climate data for November has just come in and we can see in the below charts, the difference in Mean Sea Level Pressure (MSLP) and surface winds from normal.
Large negative Mean Sea Level Pressure anomalies below Tasmania (-12) and in the Indian Ocean (-10)
Surface wind anomlalies for November, showing a clear westerly bias across the south-east of the country
It paints a clear picture with two significant negative MSLP anomalies below Tasmania and also in the south-west Indian Ocean (indicating much lower pressure than normal), along with westerly wind anomalies under South Australia, onwards across Victoria and Tasmania, north-west across the East Coast. While smaller southerly swells have prevailed across NSW, the amount of clean, autumn like mornings has been the most noticeable.
One other consequence of the SSW is that the ozone hole is the smallest on record since 1982. This is directly linked to the warming of the stratosphere, resulting in fewer stratospheric clouds forming (the surface of these cloud particles provide the catalyst for ozone depleting chemical reactions).
We're edging towards two months of negative SAM events, but how long the SSW event continues to influence the weather and surf is yet to be seen. It'll likely start to play less of a role into the end of December, but keep an eye on the site and comments below for running commentary.
The strong positive IOD event is slowly weakening, but it's delaying the onset of the moonsoon across northern Australia, and as a result we'll see tropical developments delayed into summer.
On a final note, this SSW event isn't linked to climate change per-se and is a seperate phenomena in itself, though there may be a slight causal link to the strong negative IOD event seen in the Indian Oean.
Comments
Yep they nailed it for sure and hopefully we don't see another one for a few decades. Only happy campers down here are probably wind surfers and kite boarders.
And hangliders,)
Hi Craig. Any correlation to the ridiculous run of Northerlies across SE QLD coastlines this year - starting very early out of season in June/July and ramping up till now. Been the worst I have seen and horrible for surf. I thought it couldn't get any worse on the Sunny Coast, but if this is the new norm then the only hope are wave pools lol.
Been the odd ok day at A bay, Sunshine Beach but yeah terrible overall.Also cyclone and wet season been late last few years ie shifted from Jan\feb to March\April.So a new normal for now.Looks like this year will even later but with overhang into winter.
I saw on the ABC weather the other night how Australia had its Coldest Maximum temperature ever, and I thought if this event might of had something to do with it.
"More impressively, the highest temperature recorded at Thredbo Top Station during the 24 hours to 9am on Tuesday was only -1.0 degrees. This was Australia's lowest daily maximum temperature on record" and as the article in weatherzone states: "This week's record-breaking cold outbreak occurred because the belt of westerly winds that flow between Australia and Antarctica was positioned further north than usual for this time of year. This displacement was a flow-on effect of a phenomenon called 'sudden stratospheric warming' that occurred high above Antarctica in late August and September."
Yep all related.
"Australia's lowest daily maximum temperature on record"...I'm presuming thats for December only, given places like Hotham have had max temps of -6c or so in winter.
We had a beaut night of -10C at Dinner Plain 2 or 3 years back. Went outside in my pyjamas that night to experience it. Clear skies after strong front and snow. Gave quite a few diesel cars a bit of trouble as the fuel froze in their lines. (Cue "The Day After Tomorrow" quote).
Oooops yea, November I believe.
yep
How Long did the 2002 SSW event influence negative SAM events for Craig?
Looks like into January 2003..
Remember 2002 and thinking it was the worst run in to Christmas ever...until now. Friggin westerlies and even on the west coast you have to travel a long way down to get away from the bastards.
Worst run of surf in recent memory. I've had a brand new board sitting around for about 5 weeks without a sniff. Put it in today and sat through endless Westerly squalls and short period swell. Going to book Indo season in now to give myself something to hope for.
where are you Dandan?
state, rough area.
In Tassie FR, in the south. We’ve had some average days at home, and some better than average days if you do a 3 hour round trip drive, but most surfs have been hampered by Westerlies when they’d usually be backing off by now. Swell has been okay but always 15 degrees too far West to light anything up.
Here’s hoping for a decent summer!
These articles have been excellent Swellnet. I suspect things are just getting started.
Remember when snow was going to be a thing of the past? Well, the US is breaking records:
https://flipboard.com/@WashPost/snow-cover-reaches-early-december-record...
But that's not the end of it! It seems models are predicting a NHemi SSW right after this SHemi SSW!
The resultant low temps and snowfall in the US could be something for the record books...
Question for all - has there ever been SSWs recorded in SHemi and NHemi in close proximity?
Thanks VJ, and probably no re that last question. The coming event for the NH is way earlier than normal and these events usually only occur late winter.
VJ and Craig, will this NH event have any effect on Aus/Indo surf?
Nah not at all.
Well I can report that for the lower North Island NZ it's been pretty much shithouse for the last month. Almost no south swell for the S coast, raging onshore and small on our NW coast and apocalyptically strong offshore and small on the E coast. This after one of the best winters and early springs in living memory. The SSW can go get fucked as far as I'm concerned.
Good stuff Craig
The SSW on the surf coast has been freaking awesome
sure plenty of strong westerlies, but so many days of clean 4ft+ in Nov-Dec.
This week has been 4-6 every day since Tue and still going strong into the weekend
Sorry to make you all feel bad but someone has to benefit!
Why don't you send out fricken invitations PLStocks?
Nah, it's all good. You gotta take the rough with the smooth aye. Like I said we had a pretty epic winter here so I'm still dining out on that. Also I'll be spending most on Jan in a particularly wave rich part of the country so happy days.
Actually in some ways it's good when the surf is shit-house for a while. Gives you time to get stuck into some projects round the house. It's kinda stressful when the surf's really pumping. The wife starts to get pretty grumpy with me and a lot of shit round home get's put on the back burner.
5 days of flatness, max, to do backed up chores. After that I'm ready to surf and make excuses again. My missus is au fait with that.
You're a special case though Island Bay. I've never known anyone with as much dedication to surfing as you.
IOD < > ENSO < > SAM ( The Fire Starters )
http://theconversation.com/its-only-october-so-whats-with-all-these-bush...
Well QLD is fucked, would it help if I threw some CFCs at the ozone layer?
On account of last election result.
Pretty sure Oz banished Qld to Hell.
BOM can't convince us any different.
Death Penalty is more compassionate.
VicLocal just can’t help him or herself. That’s right, I forgot the Surf Coast belongs to you. Give it a break.
Totally agree.
Been getting ripper waves at my protected local on the peninsula whilst the beachie only crew cry and carry on.
Posting here makes fark all difference to numbers.
I would have thought the other side of the Peninsula would have been a pretty good call with all the swell coming through & the wind direction (I can mention it now, event seems to be over)
Doesn't hurt to put it out there: Craig, can I please order some snowfall on the Vic Alps for December 25?
"...last event 2002"
another pattern perhaps - i think it was Dec 2002 when wicked bushfires were torching NSW, Sydney, Royal National Park, Bendalong - similar pattern to current. Related?
well the latest storm to hit the South Island was a real haymaker, regardless of the ssw having a hand in its formation, track and stalling. Weather stations around the alps picked up 1000 to 1500mm of rain, an estimated 5-6m + of snow at higher elevations, a confirmed 150cm at 1800m. It’s caused chaos with bridges washed out, landslides, tourists trapped and more than a few close calls. Interestingly it’s been proposed that Australian bushfire ash May have helped increase rainfall intensity due to rain seeding onto the dust particles or something like that....
Yeah, wow!
Particles of dust and ash (only the tiny pieces) could have definitely provided the nuclei for enhanced rainfall, will have a deeper look when I get a chance.
Crikey! That's decent precipitation. Do the NZ met use the term "inclement weather" like they do in Tassie? After a while I learned to hear that and duck for cover!
And Craig - is it over now? Is the SSW dissipated? Vic surf forecast seems a bit more negative SAM now. What a time it was.
They pretty much call it as it is over here, without emotive language. A little further up the scale than inclement that’s for sure!
Nah I heard it could be lingering for a couple more months :o
Ah jebus no, say it ain't so Craig. Give us on the Hoax Coast some hope.
AAO is about to take another dip down. Might be a pretty cool, windy Xmas in the SE
Yep, bouncing back down..
"The strong positive IOD event is slowly weakening, but it's delaying the onset of the moonsoon across northern Australia, and as a result we'll see tropical developments delayed into summer."
I'm suspecting the delay of the monsoon is what has really cruelled the spring rains across the riverina and monaro area's, well interior nsw in general.
Craig, any update on this pattern? There seemed to be some hope for rain on today's +368 charts...
No that's IOD related as that's the main influence through our spring across those regions, not the monsoon which is more related to rainfall over the north of the country.
Long-range MJO forecasts are suggesting nothing at all for our region for at least two weeks, if not a month!
Cool thanks. Yeah I'm not very good with the weather TLAs I just know that most of the spring and summer storms come from NW trough events. To my casual map reading eye drawing moisture from the tropics hence my monsoon comment.
Summer skiing!
Geez, I hope that leopard skin ski gear catches on....
That's epic, merry Christmas Craig!
The paddocks are turning even down here, but I'm spun out to see AAO down again. Take care all you crew to the north, stay safe with the fire dangers. Young one is wondering if we drive up to the Mid North coast late summer, will it all look burned? I dunno.
Went for a walk in the Nat park on the beach under the cliffs just as a little micro-front went over this arvo, was amazing to see the line of cloud just before the wind change - you could see the air getting out the way of the change, then the direction change up above and below. Not really a surfing day tho I went out early for a grovel which was fun.
Dare I pray for AAO dropping and more fronts and swell like we've had?
Merry Christmas to you too VJ!
And I love when you can see the mixing and swirling air masses! Fluid dynamics in motion.
Looks like summer taking a hold in Vico from the weekend?
Just an update for December.
We can see that the negative SAM events continued to influence the Southern Ocean with lower than normal atmospheric pressure extending from west-southwest of Western Australia to the south of Tasmania.
And also the westerly wind anomalies across Tasmania and into the Tasman Sea.
MSLP anomaly December 2019
Surface wind anomaly December 2019
Cheers for the update Craig. Generally it's been a bit more rubbish down on this coast in the recent time period, lots of SW through SE, a bit of swell here & there but junky. In between there's been a couple of offshore days with some size. There's been a two very hot days (43, 40) preceeding a front passing over. Still a tinge of green in the grass but as soon as you are inland it's looking dry as one would expect for January. Cloud cover this week and rain Sun/Mon reminded of Victoria's ability to morph back into winter looking conditions on a whim - one day of smoke from the Gippsland fires occurred before that.. Bluebottles washing ashore at times, and one followed me around the impact zone the other day.
It feels a little surreal for everything to be a like relatively normal holiday season given what has been happening around the country, both on the land up and down the East coast and in the water in Esperance. Gotta get through February though... the 2nd last last big front that came through was a dry front and those are the most concerning...
VJ - Your area gets bluebottles?
Maybe naive just didn't think they would get down that far.
Yep we do, more often if we've had a few days of SE winds in summer or around it. Maybe they come from the east coast in this scenario?
Anyway, going to grab something longboardy and go have a paddle, done my work early today.
Yeah I'd be interested to figure out where they've come from? They haven't been too bad here this year in Sydney and I'm guessing they're from a more localised source closer to you.
So I had my surf and guess what, stung by jellyfish. Walking in too. The poor thing had been all chopped up (maybe someone ran over it with their fins?) and must've been pissed. So I copped a sting. This was one of those browny ones.
Related:
https://www.independent.co.uk/news/uk/home-news/giant-jellyfish-cornwall...
Roadknight had bluebottles just before Christmas.
This is a decent front coming over for 10 January! Strong as an ox.
Surprised there hasn’t been more discussions on the link between the Sudden Stratospheric Warming and the East Coast bushfires.
Climate change, drying weather patterns and drought had primed the East Coast forests for bushfires, but the SSW looks to have been the trigger for the fire weather that has allowed the fires to explode. The negative SAM has resulted in winter like westerly winds to continue into summer, but rather than cold and dry they are hot and low humidity, pushing bushfires over the ranges down onto the coast.
Look how fast the Snowy Mountains have dried back, from snow cover in Craig’s photos at the start of December, to raging fires now. Again must be a feature of dry hot westerly winds from the negative SAM.
Yep, I've mentioned it many times over the last couple of months. It's one of the main contributors to the current devastating fire season.
Your analysis and updates have been great Craig, was more curious why the wider media hasn’t picked up on the SSW with regards to the fires.
Thanks Distracted :)
Here are the wind anomalies for January, and those Qld and those central to northern NSW surfers, you guessed it, northerlies!
Bump to thread: here's something for Craig.
Paper in Science links the Arctic Amplification to the increase of mid latitude NHemi extreme cold and snow events, catalogs an increase of these events over the last 40 years ("Winter is Coming") and attempts to construct a link between the two using SSW and SPV stretching events and their causes.
https://www.science.org/doi/10.1126/science.abi9167
"Anthropogenic global warming is projected to increase some weather extremes—for example, more heat waves and heavy precipitation events (1, 2)—but not severe winter weather such as cold air outbreaks and heavy snowfalls (3, 4). Yet, contrary to global climate model (GCM) projections, recent weather extremes have included an increase in cold air outbreaks and/or heavy snowfalls across the Northern Hemisphere (NH) since 1990 up to the recent past (3, 5–8)."
"These results have important societal implications. First, they highlight an important type of stratosphere-troposphere coupling, SPV stretching, that has been mostly hidden in the heretofore primary focus on SSWs, even though the impact of SPV stretching events on North American temperatures can be of greater extent and magnitude (31). Second, the identification of the precursor pattern to stretching events can potentially extend the warning lead time of cold extremes in Asia, Canada, and the United States. Third, our analysis is informative for policy-makers. Preparing for only a decrease in severe winter weather can compound the human and economic cost when severe winter weather does occur, as exemplified during the Texas cold wave of February 2021."
Thanks VJ, will scope tomorrow.