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Discussion in 'Systems & Severe' started by crikey, Jul 6, 2019.
Stratospheric Polar Vortex.
GFS (super-Long Range) showing an early wobble @10mb for the PV.
Same High positioning as last winter (IO region), so potentially similar forcing.
Something to keep an eye on IMO:
SAM is about to hit a brick wall post 12th July.
Is this a good thing or a bad thing. Obviously high SAM is bad, but what does a wobble mean for us?
Maybe an early sign of something good for later in the season. Probably nothing.
We saw a wobble on the models late-July/early-Aug last year and reverbs saw it wind up as one of the biggest anoms climate scientists had ever seen. Early speculation is that it's 'climate change' driven.
Not suggesting much for the snow season, but it's an anom to monitor.
This ties in with this reply I received a week or so back - I wrote to Eun-Pa Lim at the BoM asking about the changes around the 10hpa level:
Hi, I assume you are concerning about +ve/-ve SAM & yes, the forecast increase of the polar night jet around Antarctica may couple down & promote +ve SAM sometime in weekly timescale
But such change in the upper stratosphere may be favorable for spring polar vortex weakening if it is followed by substantially increased wave activity in the lower atmosphere, which may result in -ve SAM in late spring like that of 2019
So it’s good time to start monitoring the condition of the upper strato winds & surface conditions. Thanks 4 drawing my attention to this.
Great to get her reply, and love the great leveller that social media can be, where you can contact someone specific at the BoM and they get back to you. Once again the SAM is going to be one to watch. No IOD, Pacific not looking certain and the SAM offside as well? Going to be interesting late winter.
I posted this in Tassie & deep South thread fwiw.
Evidence of some decent warming in lower strat of IO polar region (26th-3th Jul)
Not a SSW event by any stretch but I'd be guessing the polar night jet will be humming with a nice kink in it this time next month.
Heat flux @ 10MB looking strong in the forecast!
Definitely could be a sign of something. Not significant as of yet for tropospheric effects, but it can become so.
Some heating evident in the upper-PV in the second week of July. Has all but corrected in the upper PV since then.
No real flow-on effects of it descending into the lower-PV.
GFS painting a picture of an Eddy Heat Flux shift in the PV, mid to long range, which could spell another minor PV warming episode over the next 2 weeks.
Interesting read here.
Had a quick flick thru , I will need another read to digest.
Yeah wow! Thanks for sharing.
Or two more reads....
Looks to have verified.
Just putting this here for posterity. A continuation of the warming event of July.
Lets see if it makes it down into the upper-trop.
For awhile now, on again off again forecast of anomalous wave 1 activity just ahead...minor warming trend at this stage which manages to penetrate the spv[all images courtesy StratObserve]...
... looks impressive on eddy heat flux anomalies....
.....with negative sam emerging up to and including mid&higher stratosphere...
If it happens..bearing in mind that its been a bit flukey from day to day...would perhaps mitigate somewhat anticipated cooling(and spv intensifying) affect of ozone depletion.
There is another thread for this type of discussion, but yes that looks really interesting.
Solid warming trend and weakening effect on most of the models.
And as you say, it looks like a w-1 attack, not sure how strong it will become at this point.
This one is certainly appears to nudge thresholds over the last 7-10 days.
35C change, puts it shy of last years event but +3-4 weeks we'll know for sure.
Interestingly, there is some coupling between upper strat and lower strat already.
Ridge establishing itself in Southern IO, but seemingly unsustainable and has backed off in the last 7 days.
LR outputs of GFS Ens suggest the ridge evolves Westward over Southern Aus where it retrogrades.
Looks like some stratospheric warming over the polar continent is coming.
Warming from wave forcing has to compete with any cooling trend from ozone depletion. The area suitable for psc formation which has generally remained above the mean since about late July, has crept back across the 2nd tercile
and the forecast for a take-off in ozone hole size is quite dramatic.
If correct, I wonder if this would put 2020 in same basket case class as pre 2005 ozone depletion era before there was a trend back towards a "healing" of the ozone hole ie: some further intensification of spv might be expected?
Here we go, just as GEFS had it's eye on a fortnight ago.
This event looks the real deal.
Doesn’t look sustained however.
Should help to keep the AAO negative though for the time being.
Nice event ending over the weekend, with the 10mb plot showing 35°C heating event in the weekending 31st August.
That’s pretty well sustained for a SHem heating event.
Quite substantial forcing in recent days.
No where near enough to reverse upper level winds but the PV looks to be in for a nice wobble over the next fortnight.
Some concurrent ridging present eitherside of the in lower strat PV (13th).
Def some warming occurring over the last week.
Looks like the final event for the PV this winter.
Lower strat warming:
Looks like the final warming event to me, IMO.
Should be registering a decent deformation by this time next week.
EC 10 day forecast, looks pretty close to the end by this stage.
Some decent warming of SPV in areas, but looks pretty standard for the end of the season.
End of gfs forecast period shows steepening rise in temps @ 10 hpa could be start of wind down for year, though perhaps latter third of these charts are a bit iffy.
@50 hpa and below, spv holding its integrity for a while longer. Thought perhaps the big decline in zmzw wind (especially @100hpa)Oct 1 or so(with a rapid acceleration other side according to gfs at least) might mirror a (final?) cold outbreak is coming...
Here's last update from British Antarctic Survey
Antarctic Situation at 2020 September 21
Antarctic ozone today: The 2020 ozone hole has grown rapidly since mid August and now covers 22 million square kilometres (msqkm), above average for the last decade. It covers most of the Antarctic continent, but is currently rather elliptical in shape, with the axis directed towards Africa. Ozone amounts are generally high around the continent as the polar vortex blocks transport further south, and are still decreasing within the vortex. Values range from around 130 DU within the vortex to well over 400 DU outside it. The area with lowest values is offset from the pole towards Africa. The vortex area near the base of the ozone layer has passed its maximum size at around 33 msqkm, and has shrunk a little to 32 msqkm which is near average for the time of year. The temperature of the ozone layer over Antarctica has passed its minimum but is below the -78°C Polar Stratospheric Cloud (PSC) formation threshold in most parts. The area with potential PSCs peaked at around 29 msqkm in July and has declined to around 18 msqkm, still a little above the average for the time of year. The temperature is mostly close to or a little below average values and is highest around Antarctica and declines towards the equator and over the Pole. The ozone hole is expected to become more circular over the coming week.
...snippet from https://www.hindawi.com/journals/amete/2017/3078079/
suggests strong relationship between ozone depletion(average total column 03) and date of final breakdown of (s)pv
First forecast I've seen of any breakdown - around 12 Oct spv near stratopause.
From: The Final Warming Date of the Antarctic Polar Vortex and Influences on its Interannual Variability , Joanna D. Haigh; Howard K. Roscoe,
J. Climate (2009) 22 (22): 5809–5819.
The following noted
Descent of breakdown varying from 10 to 40 days between 30hpa-100hpa
1.Ozone mass deficit
2.Phase of qbo(modulated by solar cycle)
Be of interest to see some metrics on relative strength of spv. At currently forecasted +4 sam at upper level, I would guess it is extremely strong against climatology. Positive sam descending to surface I think marks the evolution to maturing stage. Looks to be dearth of wave activity recently which has contributed to it's persistence (in combination with substantial ozone depletion this season thus far).
....I wonder if we might have anticipated some unusual outcome in spv evolution this season, given the unconvincing descent of the easterly phase qbo earlier this year
..thanks jellybean I had forgotten all about Dr Butler and twitterings.....
As the elongated axis of the spv cartwheels about the polar region in coming days, its tropospheric counterpart is forecast to dramatically broadside the southern Andes. Looks like substantial gravity wave activity is generated as a result.
Wave-like formations remain visible inside the spv even as late as the last week of October(as well as a noticeable long tail filament of stripped pv extended into the surf zone)
A bit to watch here. I believe there is good consensus in the scientific community that parametrization of gravity wave forcing in modelling of spv evolution is much underdone.
Still a very slow weakening of the Southern Hemisphere SPV.
Forecast to be stronger than most climatology deep into November.
I'm relying on stratobserve for this - GFS(and remainder models) seem to have zw@10hpa ramping up in short term and then easing slightly into early November, though the other models see it starting to fall significantly(which I would expect to happen).
Significant cold in lower spv, I would have thought, will offer continued support to some further ozone depletion when you consider this
and in absence of wave driven heat flux, the lower spv may prove particularly resistant to breakdown.
A lot of interest in watching this unfold. Might yet have a few twists and turns - perhaps models will struggle to map it's course because the event may prove something of an outlier?
Really appreciate your posts, but have to be honest and struggle to follow some of the details. Would like to know what outcomes you see from this event? Guess it is connected with this, which I have been following - cold anoms slowly dropping down with what I guess is an associated slow drop down through the atmopshere in the SAM - which I guess will hit the surface sometime in the next couple of months and could have an impact on the weather here in Aus, likely the opposite to last year? Am I on the right track?
Apart from noting that the transition to circumpolar easterlies marks the transition to summer and imagining the effect that delay would have generally - I dont understand enough yet to speculate much about how the evolution of the spv in a particular year is likely to nuance our weather pattern.........my focus is mostly on observations of the seasonal spv.
For search purposes -
Limpasuvan V., D. L. Hartmann, D.W.J. Thompson, K. Jeev and Y. L. Yung (2005), Stratosphere-Troposphere evolution during Polar Intensification, J. Geophys. Res., 110, D24101, doi:10.1029/2005JD006302
- amongst other things looks at features of meridional circulations in both stratosphere/troposphere though exclusively NH(I think) and a has a bit about connection to enso for instance.
Kuroda, Y. (2008), Ëffect of stratospheric sudden warming and vortex intensification on the tropospheric climate, J. Geophys. Res., 113, D15110, doi:10.1029/2007JD009550
.....both of which I'm reminded to reread myself.
There may be a few more recent, which look again at seasonal transition through the prism of stratosphere-troposphere coupling which could be useful. The majority of papers about the place though, deal with sudden stratospheric warming/ weakening of the spv I guess reflecting the frequency of these events in the NH.
It's a pity because the trend in the south since the late 90's- like this season - has been toward vortex intensification to the accompaniment of ozone depletion as most would know - with some notable exceptions -such as the split of 2002 and last years warming event - which both got some papers of interest.