Separate names with a comma.
We have a vibrant community here conversing about all sorts of non-snow topics such as music, sport, politics and technology. Simply register to reveal all our Après topics.
NOTE: This notice may be closed.
Discussion in 'Systems & Severe' started by crikey, Jul 6, 2019.
It's solid but it's not an SSW event.
Now no it looks about 315 k short in temp but keep watching @50hpa for any warming.
Yeah that's what I thought. Just needed to make sure I was on the same page as everyone.
Perhaps yet another warming scenario into mid-August.
GFS & EC both agree at this stage. Can't help but feel some abnormality/aberration in the PV this winter.
Yeah I reckon there’s more ozone up there this year via the BDC. Causing the weakening along with the interesting GWO events of this season.
Big imbalances may mark another -'ive SAM event into the latter stages of August.
JMA indicating it's close to SSW threshholds:
An important part of the furniture of ssw - so far as psv goes at least - is reversal of stratospheric circumpolar winds. Been a lot of psv disturbance this year...it may be particularly vunerable to further weakening.
Here we go folks, here’s something to talk about:
A possible major SSW event is on the horizons.....
EC ensembles for comparison. Not sure we're gonna get a split, as much as I would like to see it.
Polar Night Jet looks to get make-over though.
This looks firmly like a displacement event IMO. Still could be a major event regardless.
SSWs are fascinating...interesting to see this thread kick off with the threat of an earlier in mid July...the same time that the AAO went negative (and has sat there pretty much ever since). It's like a pattern shift kicked in at that time - something I've seen before in recent years at around this time. Has a big impact, not only for the snowfields, but also on the east coast weather, bringing dry westerlies and keeping the onshore winds away. Not sure how this upcoming event is shaping up as I don't have access to that paywalled site (I use the paid Meteologix but have not been able to recreate the charts on there so far...) Thanks all for the input, and look forward to hearing how this next event is shaping up.
EDIT: Actually that stratobserve.com site has a heap of info on it. No expert on these events by an stretch, but still looks like an event of some sort kicking in.
EC at the end of it's run, looking like a pretty solid disruption to the SPV:
But EPS Control is the real money shot, going in even harder in the D10-D15 period. That looks like major SSW territory.
the forecast warming does look quite significant. Seems to put a big "dent" in westerly circumpolar flow though maybe because of current elongation and displacement of psv towards antarctic peninsula, 60 south at mid-stratospheric level and above might not be capturing jet flow in all longitudinal sectors and thus exaggerated effect?
I know this forecast is a fair way out there, but look how far displaced the upper psv is by september.
60S (or 60N) is the standard latitude for these sorts of measurements and forecasts.
The reality is that there is a signifcant elongation and displacment of the SPV, and it will cause a disturbance at the stratopsheric level if it runs to forecast. It may be overstated or understated (latter because the vortex itself is closer to the 60S latitude).
Interested to see what it means for us - if the vortex is displacing away from Australia will that not take the westerly belt further away from us? Can see it displacing towards S America, so makes sense to have more of an impact there...although looking @ the surface on those time plots it seems to have little impact anyway - or is that impact down the line beyond the forecast period?
Sorry for the many questions - but great to have some knowledgeable folk on this forum who know this stuff...in terms of medium term forecasting this stuff is gold.
....probably one scenario none of us would want to see playout... the re-occurrence of strong high pressure cells on the perimeter of the upper psv in response to warming, ripping potential vorticity out into the surfzone. Significant O3 depletion might counter warming episodes, but this year the ozone hole has thus far been minimal. A rapidly weakening of the psv may lead to an earlier than normal breakdown = earlier transition to summer pattern.
Animation from Ben Noll:
That GIF shows the PSV being displaced over the tip of SA?
...actually I think it's exclusively the temp field which is most dramatically displaced to be centred somewhere between the tip of the antarctic peninsula and cape horn
..but I've noticed on the gfs forecasts the gph and wind fields look centred on the weddell sea. I dont know which location pv will migrate to.
NIWA here in NZ certainly seem to be onboard with the SSW. Hard to say exactly how it'll play out locally here.
Yep, even some media coverage (ok so it was stuff)
The media has hold of this - so be prepared for a mess of misinformation I am going to assume....
It’s so clear that this is going to be more significant by far, than anything we have seen this winter to date.
JB what generally causes this to happen? Is it just random events or are there many nuanced factors at play that come together for this kind of event?
Nuffie basic standard question.
Does this potentially point towards big snowfall early September?
Doesn't seem to be much correlation with Australian snowfall (based on my extensive statistical study of the population of two events haha)
Yes, there are heaps of factors that go into this process. Not a random event.
For example, the QBO, the mountain torque, tropical circulation, MSLP setups, etc, etc.
Is it just me or is ECMWF EPS showing another BIG warming hot on the heels of next weeks one at the end of it's run?
Yes. It just keeps weakening and weakening.
May be other publications out there which classify events subsequent to these. Currently forecast warming seems to put sam about -5 @10hpa.(from jellybean post above)
Weak and strong stratospheric events recompiled from:Journal of atmospheric science Vol 62," Stratosphere–Troposphere Coupling in the Southern Hemisphere", Thompson, Baldwin&Solomon.
Amplitude is in std dev of the SAM index at 10 hPa.
Year Onset date Peak amplitude
1979 (1 Oct ) -4.8
1988 (1 Aug) - 5.9
1991 (22 Oct) - 3.2
1992 (28 Sep) - 3.0
1995 (11 Sep) - 2.9
1996 (4 Aug) -3.8
2000 (17 Oct) -3.4
2002 (30 Aug) -9.8
Year Onset date Peak amplitude
1985 (10 Oct) 3.2
1987 (13 Nov) 3.9
1995 (4 Sep) 2.4
1996 (31 Oct) 2.8
1997 (21 Oct) 2.5
1998 (19 Nov) 2.5
1999 (22 Oct) 2.5
It aint easy.Microsoft PowerPoint - mcnally-bias-ws
Weakening? As in stratospheric wind speeds getting weaker? Am in interpreting your plot correctly?
The actual vortex I am talking about now.
And a weakened polar vortex allows for low pressure systems and cold fronts to escape out to lower latitudes, thus being a generally good thing in terms of bringing snow bearing weather systems to Aus and NZ? Also manifesting in negative AAO values?
And the Sudden Stratospheric Warming is the driver of the weakened polar vortex? Sorry for all the questions, just trying to piece the story together from the evolving thread.
Seems to be unusual stuff going on in the far south thus year. Earlier there was chatter about a split in the Antarctic polar vortex (into two swirls), but not sure this eventuated. Now we've got the biggest SSW scenario since 2002, potentially causing AAO values to go deeply negative. Which could potentially bring another metre of snow to the Aus, NZ Alps during September. But at this stage the effects of the stratospheric goings on haven't yet made it through to the forecast windows of the medium range weather models (or have they?)
This is my take trying to piece it all together. Comments welcome.
+2deg C stratospheric temperatures????
Yes. Just remember that there can still be inaccuracies in the Satellite data ( into the 10s Kelvin) as noted in post # 283. It is however a very significant anomaly indeed.
And the map you posted is from a forecast model run, prediction date 30 Aug. I went through the ppt from post 283 last night. But is the significance of this ppt and your comment ( I am guessing) that
the models ingest satellite temperature (or proxy, I think they were using the term irradiance) observations to initiate the model run? And therefore errors in the model initiation condition will likely propagate forwards. But errors aside, is hinting at a strong positive stratospheric temperature anomaly.
And after that is all said a done, we have the possibility of another warming the week after...
Up there with 2002 on the EHF @ 10hpa if forecast verifies.
Known as the ‘final warming’. Before the PV says goodnight and the polar night jet tapers off.
That second warming looking stronger than the first on 12Z EPS, in my eyes at least.
EHF right up there with 2002 on latest forecasts.
How to interpret the units of "Kelvin meters per second"?
Yeah there looks like there is two distinctive weakenings of the Upper Strat PNJ. It’s just a matter of how the -AAO anoms get down to the surface now. That +AAO troposphere setup in Early Sept has been there for a few GFS runs now. More and more, I think the impacts of this will stretch deeper into September and possibly early October.
The lower the value, the more heat is being transported into the PV.
Which is what weakens it through planetary waves
I think the following is consistent with jellybean
Eddy fluxes move quantities from higher to lower values. If a mean quantity increases with height, then the eddy flux will be downward (negative); if a mean quantity decreases with height, then the eddy flux will be upward (positive).
(sourcePennState College of Earth and Mineral Sciences, Meteo 300, Fundamentals of Atmospheric Science)
I will hazard that flux refers to a rate of flow through a surface or substance over time, and this is evident - hence Kelvin meters per second.