Stratosphere and Polar Vortex Watch

[Interitus]

Interesting, though maybe a couple of days out of date -

 

About-turn...

 

Edited December 2, 2017 by Interitus

[ArHu3]

31 minutes ago, Interitus said:

Interesting, though maybe a couple of days out of date -

 

About-turn...

 

 

 

Today's graph looks even better, especially compared to Thursday's but then it's today's and tomorrow might look very different ?

Edited December 2, 2017 by ArHu3
Wrong graph

[bluearmy]

Perhaps the latest gefs zonal wind forecast might be relevant - looks to me as though the predicted strengthening of the zonal flow mid upper strat may have been overdone by the gfs suite a couple days ago. Ec yesterday looks just as promising despite the trop run being less amplified hemispherically 

[Interitus]

1 hour ago, ArHu3 said:

 

 

Today's graph looks even better, especially compared to Thursday's but then it's today's and tomorrow might look very different ?

It's the same run, this graph is at 65°N, the other is 60°N

[ArHu3]

1 hour ago, Interitus said:

It's the same run, this graph is at 65°N, the other is 60°N

Where is 60 degrees hidden? I guessed the direct link for that graph but is there an overview page somewhere? 

[Dennis]

lets see if this will game on

[lorenzo]

Interesting look by day 10 on Berlin this morning..

to get the 60N plot just change the 65 in the url to 60

[Dennis]

some good progress in the strato 

[Dennis]

 

[Shuttler]

Hi. Can the more learned on this forum possibly explain why the Trop and lower Strat has been so de-coupled from the Upper Strat since Sept ? And set to continue for much of Dec by the looks of latest Ens and weekly fcasts (ECM46). I expect phases of this but it seems unusual to see such longevity in the winter half of the year. I'm trying to understand what may be driving the perpetual Arctic blocking and -AO signature in the absence of any sig downwelling from the upper Strat. Are we looking at a greater influence from the reduced Arctic sea ice or SAI this season, perhaps ? I do wonder if a split SSW (as I'm expecting this Jan) would break the Strat-Trop de-coupling we're currently seeing, though of course this is likely to induce further Arctic blocking for the second half of the winter. Any suggestions appreciated - with the ultimate aim of improving seasonal guidance !

 

[Interitus]

8 hours ago, Shuttler said:

Hi. Can the more learned on this forum possibly explain why the Trop and lower Strat has been so de-coupled from the Upper Strat since Sept ? And set to continue for much of Dec by the looks of latest Ens and weekly fcasts (ECM46). I expect phases of this but it seems unusual to see such longevity in the winter half of the year. I'm trying to understand what may be driving the perpetual Arctic blocking and -AO signature in the absence of any sig downwelling from the upper Strat. Are we looking at a greater influence from the reduced Arctic sea ice or SAI this season, perhaps ? I do wonder if a split SSW (as I'm expecting this Jan) would break the Strat-Trop de-coupling we're currently seeing, though of course this is likely to induce further Arctic blocking for the second half of the winter. Any suggestions appreciated - with the ultimate aim of improving seasonal guidance !

 

Why do you say it is decoupled?

[Shuttler]

14 minutes ago, Interitus said:

Why do you say it is decoupled?

I don't see much downwelling of lower heights from the Upper Strat in the past 3 months or so. Compared to earlier this year for example, as is fairly evident I think from the time series plot. Just trying to understand what causing the perpetual positive GpH in the lower Strat and Trop (and Arctic blocking) since Sept.

[Summer Sun]

 

[snowking]

12 hours ago, Summer Sun said:

 

That is an awesome index! It would be good to get something like that developed for public access (I'm assuming Michael's one would be behind the WSI paywall?) even if it were GEFS/NAEFS based

Edited December 5, 2017 by snowking

[bluearmy]

Note that zonal flow slowly picking up a bit as the strat Alaskan ridge pulls back away from the pole a tad. Also, through week 2 the gefs is retrogressing that ridge towards the aleutians. 

[Paul_1978]

19 minutes ago, bluearmy said:

Note that zonal flow slowly picking up a bit as the strat Alaskan ridge pulls back away from the pole a tad. Also, through week 2 the gefs is retrogressing that ridge towards the aleutians. 

Good news or bad regarding the Aleutian ridge?

[bluearmy]

13 hours ago, Paul_1978 said:

Good news or bad regarding the Aleutian ridge?

I quite like aleutian ridges from experience - others will have a different viewpoint 

It all boils down to the locale and strength  of the Canadian vortex as far as the Atlantic profile is concerned. A retrogression of the Alaskan ridge should pull the n American trough and pv west a bit too. 

 

[SteveB]

I sure I saw somewhere  on hear about the vortex gaining strength around now & setting up shop in it's usual location. If it hasn't done this by now, then it's fairly likely that we can start calling this Winter differently

My question is, what is the current situation regarding the vortex, is it still dis-organised ?

[Fiona Robertson]

Forecast animation looks tasty

https://www.netweather.tv/charts-and-data/stratosphere

[snowking]

8 hours ago, SteveB said:

I sure I saw somewhere  on hear about the vortex gaining strength around now & setting up shop in it's usual location. If it hasn't done this by now, then it's fairly likely that we can start calling this Winter differently

My question is, what is the current situation regarding the vortex, is it still dis-organised ?

I think this tells the story quite well vs last year at the moment:

As you can see, just as we are reaching the point where last year we saw rapid vortex intensification, this year we are heading in the opposite direction - not a technical SSW but a very weakened stratospheric vortex and a pattern which is still being largely driven by the troposphere in all reality (with further wave flux driving up into the stratosphere to come courtesy of our upcoming Scandi/Siberian high & Aleutian low combo) with some fairly notable Wave 1 forcing further aloft too:

In terms of how organised the vortex is/isn't, well hopefully you already know that tropospherically the vortex is somewhat in tatters and will remain so for some time to come yet into the medium range period. In terms of the stratosphere (with the caveat that this is yesterday's 0z ECM run):

You can see the results of that Wave 1 forcing further aloft, with a lot of pressure being placed on the vortex from the Pacific side, knocking the usually rock-steady spinning plate off its usual central axis and over towards the Siberian sector instead.

So other than right at the very top of the the stratosphere where we see a forecast increase in zonal wind speeds:

The vortex is not looking like a particularly happy chappy. But that last point is the one I wanted to drive home here - just because it's all rosy just now it doesn't, unfortunately, mean we can absolutely write off downwelling of a stronger zonal winds from the stratosphere into the troposphere as we head further into the winter.

However, given the current direction of travel of global angular momentum budgets, further wave flux likely to be driven up from the troposphere, an Easterly QBO and of course the lack of distinct coupling presently between the troposphere and the stratosphere, one very much hopes that we are looking at the most favourable conditions for quite a few years if you are of the colder persuasion (or as I like to think of it, the light side of The Force), with the vortex being battered and bruised and awaiting some sort of potential knock out blow - to be clear, I can't see that knockout blow in any current output, but it looks primed to be knocked out should that blow come.

'62 was an analogue for me, but I'm not sure we are quite staring down the barrel of anything quite that significant yet. Certainly struggling to see anything especially mild in the outlook that's for sure.

Edited December 6, 2017 by snowking

[SteveB]

Thanks Snowking, was kind of what I thought reading what was said in this thread and on twitter.

Whole Winter is looking promising, what could possibly go wrong.

[Paul_1978]

How are stratospheric winds actually measured? Presumably there's no anemometers up there .

[Dennis]

6 hours ago, Paul_1978 said:

How are stratospheric winds actually measured? Presumably there's no anemometers up there .

You mean this ........actual winds strato

[FetchCB]

7 hours ago, Paul_1978 said:

How are stratospheric winds actually measured? Presumably there's no anemometers up there .

According to this paper it's done via satellite doppler radar 

http://journals.ametsoc.org/doi/pdf/10.1175/JTECH1880.1

Ithink that also weather balloon data may also be used 

[Interitus]

On 12/4/2017 at 20:17, Shuttler said:

I don't see much downwelling of lower heights from the Upper Strat in the past 3 months or so. Compared to earlier this year for example, as is fairly evident I think from the time series plot. Just trying to understand what causing the perpetual positive GpH in the lower Strat and Trop (and Arctic blocking) since Sept.

At its most simple, as geopotential height is proportional to virtual temperature, perpetual positive GpH in the lower strat/trop reflects anomalous warmth and lowering upper strat heights or thicknesses shows cooling. Critically important - upper height changes can only indirectly affect heights at lower levels or the surface through ageostrophic circulations. To quote Steenburgh & Holton from "On the Interpretation of Geopotential Height Tendency Equations" (1993) https://atmos.washington.edu/~gcg-dlh/JR_site/papers/1993_3.pdf

Quote

Assuming hydrostatic balance, only two processes can alter the geopotential height of a given pressure surface: 1) a change in the mean virtual temperature of the column of air below that pressure level, and 2) a change in the total mass of the air column due to net mass divergence or convergence. Virtual temperature change above a given pressure surface cannot alone cause a change in the geopotential height of that surface.

This is worth absorbing and it follows that time/geopotential height cross-sections may not be the best indicators of trop/strat linkage. 

It all depends on what exactly is the nature of, and what is referred to as troposphere-stratosphere coupling. A common indicator is by annular mode i.e Arctic oscillation and stratospheric NAM, as used in the well known charts from Baldwin and Dunkerton to show the downwelling of zonal wind anomalies following SSW. If limited to this it could be argued that the recently moderately strong higher vortex is decoupled from the lower strat / trop - Snowking above referred to a 'distinct lack of coupling'. However, the wave/mean flow interaction which we are seeing at the moment weakening the strat vortex is obviously also a form of coupling!

Peter Haynes summed up coupling well in SPARC newsletter 25 (bold my emphasis) -

Quote

Baldwin and Dunkerton (1999, 2001) have shown that the vertical structure of NAM variation in NH winter typically shows a downward propagation from middle stratosphere to troposphere and the corresponding figure from their 2001 paper is now (quite justifiably) de rigeur in any scientific talk in this area. Does this picture imply a direct effect, with some delay, of anomalies in the stratospheric circulation in mid-stratosphere on the troposphere?

The answer is ‘not necessarily’. The equatorial quasi-biennial oscillation (QBO) is an educational example. The QBO is manifested by downward propagating anomalies in zonal wind, however it was pointed out by Plumb (1977) that, at least in simple dynamical models of the QBO, there is in fact no downward propagation of information. The evolution of the flow below some given level is completely independent of any changes that are made above that level. The distinction in elementary wave theory between phase propagation on the one hand, and group propagation on the other,
with only the latter unambiguously associated with propagation of information, is well-known. The downward propagation of wind anomalies in the QBO can be seen as a sort of phase propagation.

Simple dynamical models of the equatorial QBO of the type studied by Plumb (1977) are not necessarily relevant to the extratropical stratosphere, in particular because rotation is omitted and because a WKBJ approximation is used in calculating the structure of the waves for given mean flow. However
Plumb and Semeniuk (2003) have shown in a simple wavemean model of the extratropical stratosphere (that does incorporate rotation and uses a
weaker approximation for the spatial structure of the waves) that forcing at low levels can give rise in the stratosphere above to downward propagating
structures similar to those observed by Baldwin and Dunkerton. Therefore, such structures do not necessarily imply downward propagation of information.

There is similar uncertainty in interpretation of the correlations between anomalies of zonal velocities and wave fluxes of the type shown by Hartmann et al. (2000), (Figure 1), for example. While these correlations strongly suggest dynamical connections between troposphere and stratosphere involving two-way interactions between mean flow and waves, it is impossible to tell from the correlations alone whether there is an effect of the stratosphere on the troposphere, or the troposphere on the stratosphere (or indeed whether it makes sense only to think of the troposphere-stratosphere system as intrinsically coupled, with the whole idea of the effect of one component on the other as intrinsically flawed).

Notwithstanding the above, there are now many examples of simulations in numerical models where changes in the troposphere have been shown to result from imposed changes in the stratosphere. In these cases downward propagation of information is difficult to discount. Some relevant examples include imposed perturbations to the upper stratosphere (Kodera et al. 1990,Gray 2003) as a simple representation of solar cycle effects, changes to stratospheric radiative equilibrum temperature profiles in a simplified general circulation model (Polvani and Kushner 2002, Kushner and Polvani 2004), changes to Southern Hemisphere stratospheric ozone in a general circulation model (Gillett and Thompson 2003) and changes to stratospheric initial conditions in a numerical weather prediction model (Charlton et al. 2004). The results of Scott and Polvani (2004), obtained in a simplied dynamical model with a damped troposphere, show nicely that the wave flux from troposphere to stratosphere cannot be considered to be set by the tropospheric wave forcing alone and that the stratosphere can to some extent determine how much wave flux it accepts.

http://www.atmosp.physics.utoronto.ca/SPARC/News25/coupling.html

There has been much research in the 12 years since this was published, advancing many of the ideas which are described therein, but a definitive description of coupling processes still doesn't appear to be complete.