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Stratosphere temperature watch - 2016/17


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On 1/9/2017 at 12:25, Interitus said:

we can see the main wave 1 component at 500mb become established, quasi-stationary over the Atlantic -

216.png

Upwards propagation of wave 1 typically takes place at roughly ~6km per day, so should reach the 100mb around 10000 metres higher within a day or two, with a westward displacement or tilt, and indeed this is what is seen over the next couple of days -

264.png

During this time, the 10 and 1mb levels are influenced by waning previous wave 1. It takes 4+ days for the new wave to reach from the troposphere to 10mb and above, and at the end of the run we see it appear, with a further westward tilt -

336.png

 

On 1/25/2017 at 16:57, Interitus said:

As this SSW is wave 1 from essentially Atlantic side blocking, is the tendency of the GFS to steamroller this away resulting in reduced or shortened forcing compared to the other models?

Just to recap the progress of the warming from earlier posts above, with an initial wave 1 followed by the main wave 1, they can be roughly identified in the NCEP blocking chart below as highlighted. It is interesting that the initial Pacific wave 1 was well forecast to day 10 and even noticeable at day 12. However, the Atlantic based wave 1 which has initiated the SSW was poorly forecast beyond day 7, thus perhaps confirming suspicion of Atlantic zonal bias in this instance, with ramifications for the SSW forecast and also obviously for the weather in the UK/Europe in general as the ongoing blocking persists -

9panel_ghgs_nh_ed.thumb.png.f24134e8da7cb4ea8094b2c639e38d7a.png

Though to be fair, if yesterday is confirmed as a reversal, the GFS chart below from 19/01 was pretty accurate -

On 1/19/2017 at 07:24, Interitus said:

Z_temp_10hpa_312_17011900.png

Bit of a surprise.

 

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The current projected Wave 1 displacement of the stratospheric vortex looks to be following the script nicely. During the last few days and for the next 2-3 we will see a series of unusually deep

Well this is getting interesting and a possible game changer. Why chop down a tree when you can squash a seedling ? Following the lead of the models of late last week, we have begun to tick down

The importance here I think is the consistency over the GEFS in terms of pretty much all the ENS members falling below zero and obviously indicating a wind reversal, to an extent the GFS DET can do wh

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On 1/31/2017 at 19:49, Catacol said:

airly swift recovery forecast... and we had a similarly swift vortex recovery in December. For the start grogs out there - is this the strong wQBO at work or is it some other factor? I don't recall seeing such swift vortex recovery from stressed states in the past but maybe my memory is playing tricks on me.

OK, by identifying 10mb zonal wind minima as the lowest wind speed over a 21 day period (central date +/- 10 days) and then finding the maximum wind speed within the following fortnight, there is a correlation of only 0.06 between wind increase and monthly QBO i.e. no significant relationship.

The average increase by month is -

Oct 9.83 m/s

Nov 16.78 m/s

Dec 22.47 m/s

Jan 21.50 m/s

Feb 20.34 m/s

Mar 12.48 m/s

Apr 5.00 m/s

This displays a clear seasonal signal and the reason should be fairly obvious. The wind speed might be expected to be a balance between temperatures recovering post-warming and the amount of further perturbation and wave activity. Hence the largest increases are found during the period of shortest days when the stratosphere is at its coldest, and with the greatest chance of radiative cooling to help temperatures recover.

The GFS 06z forecast of 27 m/s for 15/02/16 is (subject to fluctuation) slightly above average for February or winter average of 21.38 m/s but within 1 s.d. (29.56 m/s) and a lot less than record of 42.13 m/s just last year on 09/02/16 (from 11.53 to 53.66 m/s, QBO 6.77) or 2nd place 40.34 m/s from 04/12/81 (-3.08 to 37.26 m/s, QBO -12.31)

 

 

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16 hours ago, Summer Sun said:

 

He's a bit behind the game considering I posted this on the mod thread 4 days ago -

umedel60_17012906ed.thumb.png.b5efacce811714432008713211524fdd.png

https://www.netweather.tv/forum/topic/87058-model-output-discussion-25th-jan-the-final-third-of-winter-beckons/?page=15#comment-3534630

edit: It's interesting that the Attard GFS forecast animation linked in that post still shows a coupling between the stratospheric 10mb and tropospheric 500mb anticyclone as they move from Alaska into eastern Siberia -

http://www.atmos.albany.edu/student/hattard/realtime/dt_500/DT_500.php

In light of Cohen's comment about classic downward propagation of weak polar vortex to surface, it is worth considering what mechanism may be at play here, and what is meant by 'classic'. The 'classic' reviews do show some quick response but also more generally over a period of weeks for propagation of anomalous zonal wind, based upon composites of numerous events which blur the mechanisms behind this. This leads to the rather vague 'will it/won't it propagate?' and 'what will be the effects?' kind of questions. At the present time, a better explanation might be found in the work of the likes of, for example, Harnik, Shaw and Perlwitz, with a quick response through downward wave reflection/coupling at the actual time it is occurring.

 

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4 hours ago, Nouska said:

This will please those who were looking at comparisons with 1991 - similar distribution of the separate lobes and a proper split this time.

06Zaa70dd679e81ad87bc7e675ca99f378d.gif1991 psnh_pen_hist_z30_199108.gif

Potentially a wintry March?

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2 hours ago, karyo said:

Potentially a wintry March?

Was there a SSW late Jan 1991 - if so then it was a very quick response with the cold in very early Feb, it didn't last too long though, 2 weeks at best, remainder of Feb 91 was mild and March 91 not especially cold at all.

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1 minute ago, damianslaw said:

Was there a SSW late Jan 1991 - if so then it was a very quick response with the cold in very early Feb, it didn't last too long though, 2 weeks at best, remainder of Feb 91 was mild and March 91 not especially cold at all.

Ok but the chart above is for 20/2 so I'd think it would spill into March comfortably. I love a cold March! :D

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1 hour ago, damianslaw said:

Was there a SSW late Jan 1991 - if so then it was a very quick response with the cold in very early Feb, it didn't last too long though, 2 weeks at best, remainder of Feb 91 was mild and March 91 not especially cold at all.

No technical SSW in 1991 but this year following a very similar script as @bobbydog has been commenting on in the model thread.

Strong warming end of January '91

   archivesnh-1991-1-28-12-4.png

(Note core cold centred to north of UK as was the case last week.)

The vortex partly splits into two lobes and is rapidly followed by development of Scandinavian high pressure. I cannot see if this is up or down influence as no archive of the different levels from back then. The vortex reformed by mid month and allowed the Atlantic train back on the tracks.

archivesnh-1991-2-4-0-0.png     psnh_pen_hist_z30_199111.gif

Looking at the GFS strat forecast and reading between the lines of a Fergieweather tweet about GloSea - a proper and lasting split may follow this one but as to what the surface conditions would be to see out February and usher in Spring ..... We know a cold March can follow a decent split from the events of 2013 but the picture is far from the scattered vortex profile that was present at this stage in 2013.

psnh_pen_hist_z30_201308.gif

An edit to add the archived MJO chart from February 1991 - similar phasing to current forecast but a much lower amplitude.

rmm_199102.png

 

 

 

Edited by Nouska
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15 minutes ago, Nouska said:

 ..... We know a cold March can follow a decent split from the events of 2013 but the picture is far from the scattered vortex profile that was present at this stage in 2013.

psnh_pen_hist_z30_201308.gif

 

 

 The one on the 18z GFS is exactly that!!!  

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1 hour ago, damianslaw said:

Was there a SSW late Jan 1991 - if so then it was a very quick response with the cold in very early Feb, it didn't last too long though, 2 weeks at best, remainder of Feb 91 was mild and March 91 not especially cold at all.

I think 99% of us would take that in 2017!

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13 hours ago, Isotherm. said:

I have not been optimistic this winter from a CONUS standpoint insofar as the stratosphere, due in part to preset background conditions, and ongoing modulatory effects of mechanisms such as EEP via geomagnetic activity, robust westerly shear stress via the QBO, and poor tropical forcing. Additionally, up until the past couple of weeks, the brewer-Dobson circulation has been weaker than normal w/ concomitant decreased ozone transport. That has since improved dramatically. The alterations in late January via Aleutian stratospheric ridging and subsequent w1 forcing converging at the vortex has led to a technical SSW w/ much more susceptible vortex. It always appeared to me that reconsolidation would occur, but the question in my mind was the extent to which subsequent w2 assaults would impact the circulation. The upcoming period will feature enhanced w2 generation with a classic constructive interference regime across the northern hemisphere, in conjunction with propagating MJO wave signal. This will induce further Rossby wave driving applying more pressure to the vortex. As the U signal circulates the globe, we should see - initially - the low geopotential heights approach the W US Coast followed by retrogression, as well as the development of the first genuine -NAM/NAO of the winter. Some of the latest model data has been detecting the impacts of the w2 forcing on the vortex with the upwelling splitting activity throughout the stratosphere. If this occurs, my thinking is that the resultant tropospheric transformations would be fairly rapid due to present conditions, the nature and origin of this attack, and ongoing weak circulation further up in the atmosphere. Overall, it is difficult to ascertain low level impacts right now, but my confidence has been high on a AO/NAO reversal for mid February into March. Of course, we could revert to the base pattern; that's always a possibility, but I think the evidence is sufficiently strong to argue against such a notion at this juncture.

By the way, I have been reading this board for awhile, and I think there are some very talented individuals posting here.

Hi @Isotherm.. and welcome to the forum.

A great first post and I certainly agree with your thoughts, certainly that the SSW is helping drive the MJO and then this in return creating the conditions for wave 2 activity to return the favour upwelling into the strat. Will the ECM smell the coffee as it looks like the GFS already has.

Edited by chionomaniac
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1 hour ago, chionomaniac said:

Hi @Isotherm.. and welcome to the forum.

A great first post and I certainly agree with your thoughts, certainly that the SSW is helping drive the MJO and then this in return creating the conditions for wave 2 activity to return the favour upwelling into the strat. Will the ECM smell the coffee as it looks like the GFS already has.

Thanks for the welcome chiono. Below the 10hpa level, the ECMWF does have a split precursor appearance by the 15th. It could simply be a timing difference with the euro slower. But it is incontrovertible that the precursor pattern is strikingly w2, so I would expect the 10hpa level to acquire more of that appearance. It is possible euro / slower may be correct as MJO forcing likely won't peak until 15-18th on the vortex. GFS is correct on the w2 signature but it certainly isn't impossible that it is a little quick on the trigger. Either way, interesting stratosphere tracking ahead.

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8 hours ago, Weather-history said:

Got to say the Atlantic doesn't look like now it will dominate the rest of winter. The Atlantic hasn't really dominated this winter, there have been a few burst of it but the story of this winter has been quieter with anticyclonicity being the dominant.

@Weather-history; Certainly for the north and west of Britain it does not seem to have been a cold winter to date. Where I live in the North Pennines I am yet to see the temperature drop below -5C (unusual for us at over 400 metres above sea-level not to get below this temperature) and we have only had 8 cm of snow-cover at most. The high-pressure systems this winter have tended to be over Europe, sometimes extending across the South and this is not a good position for very cold conditions with hard-frosts for the North Pennines. This part of the country has often had mild air off the North Atlantic whilst the South East has had dry cold and frosty weather under high-pressure.

That said, the (predicted) circulation far aloft over the Arctic and sub-arctic gives more grounds for optimism (as regards cold weather and snow) over the next fortnight and certainly for those of us living in the north of England the longer-term forecast charts (which have strong high-pressure over Scandinavia) there are prospects for the coldest weather this winter to date. In early January the predicted mean winds at 10 mb were over 30 m/s (67 mph or more) along 60N and the strong westerly QBO high over the Equator looked like it might help maintain the strong upper flow; thanks to upwards wave activity over the tropics associated with convective disturbances (leading to subsidence and warming in the Arctic Stratosphere) since early January the 10 mb level westerlies averaged along 60N are now much weaker ( and predicted to remain so) leading to the surface synoptic set-up with high-pressure over Scandinavia expected this week. if it comes off I, for one, will be quite chuffed!  

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Some great theories above, but it looks like it is the GFS which is starting to smell the coffee with a renewed wave 1 attack like the ECM, rather than the sequence of wave 2 splits which it pulled out of nowhere for a number of runs at day 10 onwards. The ECM or GEOS/MERRA have not shown any great wave 2 amplitude, indeed it is below 'average'. Of course there are theories of vortex splitting from exciting the resonance of the barotropic mode which can occur with relatively low wave 2 forcing, but I have no idea if the GFS can handle this. On the subject of wave number it can be seen from the reanalysis data that wave 1 is dominant for nearly all SSW regardless of whether it is a split or displacement, only 4 in the MERRA data have dominant 10mb wave 2 for the fortnight prior to reversal. This is confirmed by this interesting recorded presentation from the 2015 AMS conference which examines this in more detail and makes the surprising suggestion that wave 1 can actually transform into wave 2 in the stratosphere as they describe -

Quote

Preliminary results suggest that, against common belief, the dominant wavenumber of the energy flux into the stratosphere might not determine the type of the SSW as the wavenumber 1 component is largest at almost all times. Instead, differences in the wave-wave interactions within the stratosphere are responsible for the split of the polar vortex.

https://ams.confex.com/ams/95Annual/webprogram/Paper256393.html - click on "Recorded Presentation" link to view.

With regards SSW-MJO(-SSW?) and in reference to this 10hpa temperature anomaly animation doing the rounds -

temp10anim.thumb.gif.abaf0d1d9de360cd750ec3d5f9172b22.gif

Yes, at the time of the stratospheric warming in the Arctic, meridional circulation creates a commensurate cooling over the tropics which, theory goes, enhances tropical convection. Except this is at 10mb, there is no convection at this level. The cooling needs to be in the lower strat/upper troposphere (see eg. Kodera (2006) paper Influence of stratospheric sudden warming on the equatorial troposphere) and as can be seen in the plot below, cool equatorial anomalies only feature lower down at the end of run, at around the time of the projected MJO peak amplitude (with possible uplift showing in cool mid-trop anoms).

T_10s10n.thumb.jpg.142a650580fc0d3f082a044469d2bdc4.jpg

Factor in propagation time for any extratropical waves, then more for vertical propagation and a wave 1 displacement is probably already under way.

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I just think this has been a drawn out 'final warming'? Last year we saw an early final warming in late feb so disruption leading to final collapse would seem to be the way we are headed. As far as 'forecasting ' is concerned we've not been able to look beyond day 3 all winter!!!

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54 minutes ago, Gray-Wolf said:

I just think this has been a drawn out 'final warming'? Last year we saw an early final warming in late feb so disruption leading to final collapse would seem to be the way we are headed. As far as 'forecasting ' is concerned we've not been able to look beyond day 3 all winter!!!

Mounting evidence for the excessively warm Arctic troposphere altering the typical seasonal progression as even near-average amounts of wave breaking have greater resources to work with. Coupled with reduced trop-strat heat transfer during quiet WAFz periods due to GHG blanket, perhaps a great many of our winters will tend to see a vortex that gets very strong, very fast, then takes a hammering later in the season.

All hypothetical though, and I shall (at least) wait and see what happens in an E-QBO, low solar activity autumn-winter before drawing conclusions.

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