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39 minutes ago, Dennis said:

full hit by Polarvortex 

64.png

For n Scandinavia Dennis. - yes indeed! 

zonal wind charts not as impressive as yesterday's Berlin output but they were never going to be. this morning looks quite reflective of the 00z run though late on the Atlantic seems to more awake which is probably reflective of the trop profile.

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10 minutes ago, Glacier Point said:

And the importance of the Siberian High - Aleutian Low combo,

5a169d3e2f24f_2005mslp.thumb.jpg.863e397d37a3f9a5e896b7ed2e8ca60e.jpg5a169da5c25aa_2006t.thumb.jpg.ea016e32419048e66ebc8555cfdcfdb1.jpg

What are your thoughts going forward Gp,regards strat this winter.

I know your busy and we appreciate your time and thoughts.

Be lovely if you posted in mod thread.

Yes I'm greedy lol.

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As @recretos has showed, the GEFS are not always reliable at 10hpa. It’s a shame that strat data from the eps isn’t available on weatherbell. Do any paywall sites offer this ??

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5 hours ago, Glacier Point said:

 This year's vortex refuses to cool in its core, the cooling events always around the periphery..so temperature plots are not going to be a reliable guide.

 

This is just not the case - from the MERRA data https://acd-ext.gsfc.nasa.gov/Data_services/met/ann_data.html currently the temperature is below average at every level (10mb, 30mb, 50mb, 70mb, 100mb, 150mb) at 90°N, 80°N, 60-90° zonal mean and 55-75°N zonal mean.

Cooling is progressing normally, and ignoring long term background drivers such as BDO driven subsidence and stratospheric CO2, immediate temperatures are a balance between radiative thermal relaxation (cooling) and wave driven heat flux and baroclinic subsidence (warming) - an indication of the recent lack of these warming effects at the moment can be seen in the below average 45-day mean heat flux charts eg -

4575vTmean30.thumb.png.de9cbfb1b6159602ec8370cbd87495e4.png

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19 minutes ago, Interitus said:

This is just not the case - from the MERRA data https://acd-ext.gsfc.nasa.gov/Data_services/met/ann_data.html currently the temperature is below average at every level (10mb, 30mb, 50mb, 70mb, 100mb, 150mb) at 90°N, 80°N, 60-90° zonal mean and 55-75°N zonal mean.

Cooling is progressing normally, and ignoring long term background drivers such as BDO driven subsidence and stratospheric CO2, immediate temperatures are a balance between radiative thermal relaxation (cooling) and wave driven heat flux and baroclinic subsidence (warming) - an indication of the recent lack of these warming effects at the moment can be seen in the below average 45-day mean heat flux charts eg -

4575vTmean30.thumb.png.de9cbfb1b6159602ec8370cbd87495e4.png

I admit i am no expert and just say what i see.The graph you show does indeed show temperatures dropping but it can be confusing looking at those.For example based on the mean zonal winds data the vortex is weakest around the pole and this appears to be reflected in the temperatures showing some warming at latitudes 80/90N  at the lower levels(50hPa)-here

t80n_50_2017_merra2.pdf.bce8eab0574394e468c19305369e9fdc.pdf

t90n_50_2017_merra2.pdf

Anyhow just scanning through the latest data and we see continuing evidence of wave breaking..The Tokyo site shows this has been ongoing since early Autumn with .the obvious effect on the vortex at lower levels.

jikei_uep_nh.gif

Zonal winds increasing at the top but being neutralised from filtering down to lower levels.

According to latest ECM forecasts still the same picture going forwards days 5/10

ecmwfzm_u_f120.gifecmwfzm_u_f240.gif

The blue(negative)readings persisting at high latitudes up to 20hPa -not an official major warming but certainly that vortex has been undermined by the ongoing heat fluxes and looks like it will still be weakened going into December.

Edited by phil nw.
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30 minutes ago, phil nw. said:

I admit i am no expert and just say what i see.The graph you show does indeed show temperatures dropping but it can be confusing looking at those.For example based on the mean zonal winds data the vortex is weakest around the pole and this appears to be reflected in the temperatures showing some warming at latitudes 80/90N  at the lower levels(50hPa)-here

t80n_50_2017_merra2.pdf.bce8eab0574394e468c19305369e9fdc.pdf

t90n_50_2017_merra2.pdf

 

The heat flux graph posted not so much shows temperatures dropping directly but below average wave activity meaning lack of warming influences.

In the two graphs linked to above, the warming is in the forecast, not what they are at present.

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5 minutes ago, Interitus said:

The heat flux graph posted not so much shows temperatures dropping directly but below average wave activity meaning lack of warming influences.

In the two graphs linked to above, the warming is in the forecast, not what they are at present.

The lack of warming influences as you put it Interitus has certainly kept the lower vortex under strength at it's  core though.Pretty much i think what GP said in his post.:)

 

 

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30 minutes ago, phil nw. said:

The lack of warming influences as you put it Interitus has certainly kept the lower vortex under strength at it's  core though.Pretty much i think what GP said in his post.:)

Sorry, again using the MERRA data (this time from https://ozonewatch.gsfc.nasa.gov/meteorology/wind_2017_MERRA2_NH.html which includes percentile deviation), the average November 2017 vs long term mean 60°N zonal winds are

10mb 28.99ms - 28.08ms

30mb 18.19 - 18.08

50mb 15.64 - 15.43

70mb 14.74 - 14.35

100mb 14.66 - 13.81

150mb 15.89 - 13.92

All just slightly above average, interestingly apart from the lowest level at 150mb which is above the 70% level (ie in top 30%).

It is normal for the core of the vortex to have weaker zonal wind than the heart of the polar night jet eg. from NCEP reanalysis the 30mb November zonal wind at various latitudes -

60°N - 16.86ms

65°N - 17.27ms

70°N - 16.67ms

75°N - 14.67ms

80°N - 10.94ms

85°N - 5.69ms

Now, although it wasn't mentioned by GP, you are correct, depending how it is defined, the "lower vortex core" does have lower zonal winds than normal -

1711Uanom.thumb.gif.6abce2346ec7af0104230c4e7eaf4c50.gif

But notice how this is compensated for by a stronger night jet. The reasons for this are that the vortex has been less disturbed so the wind distribution has not been spread about, and also because the lower vortex is larger than average -

vortexarea.thumb.png.548a6dfde79f2b0baf6a976b8ff0224c.png

It is certainly not due to lack of cooling, as shown by the temperature anomalies -

1711Tanom.thumb.gif.aec6cf8babc1a17761121b818547d392.gif

 

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Great discussion - have not see the PV plots before. Interesting viewing..

https://ozonewatch.gsfc.nasa.gov/meteorology/pv_2017_MERRA2_NH.html

Translating size and shape from the graph above re:vortex size is easier imo with something more visual to follow, this is where the animations are excellent and totally spell binding - can drift watching these when there are wave breaks.

https://acd-ext.gsfc.nasa.gov/Data_services/arctic/index.html

Opening the animation details the PV layer and hPa for guidance vs the other data usually referred to.. here are a few vorticity ones in image format for referral and this page also has temp profiles.

EPV_2017112100_A_380.thumb.png.bbd9c543dab5ca40cf7650dfd227cbf4.pngEPV_2017112100_A_440.thumb.png.00a5293a76a6883eb91c1f5a3383cb29.pngEPV_2017112100_A_600.thumb.png.8d4a7bf947c0caf590f995155f0d0e58.pngEPV_2017112100_A_800.thumb.png.616a51f1761b0939924af76f101e791e.png

T_2017112100_A_50.thumb.png.411ea1085a4563129b0cc762170798c6.png

Our GEFS suite is 12/8 for u wind reversal on Hannah Attard's page today, we all know it likes to misbehave however...

Edited by lorenzo
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Would welcome people's thoughts on how they think the very active hurricane season and heat transported from the tropics has had on the emergence of the Polar Vortex this year. I suspect it has had the effect of weakening its potency somewhat..

Interesting to note potential comparisons with winter 05/06, that year came on the back of an equally very active hurricane season. There was alot of mid atlantic ridge development that winter, but it never quite linked up with the siberian high, and we were left prone to a northwesterly airstream in the main, but lots of frost and preety cold temperatures, it wasn't until later in Feb easterlies arrived. Had we seen such a link up then a very cold winter would have occured no doubt. East europe and west russia were especially cold in January. We also saw a wintry cold latter part to November with northerlies, very similiar to synoptics on offer currently..

Anyhow we seem to be starting the winter in a different situation this year with regard to the strat, lots of heat being pulled into the Poles.

Edited by damianslaw
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@Interitus given @damianslaw view of the last signature Hurricane input and @Glacier Point input on forthcoming East Asian Mountain Torque inflection - wondered with your subject matter expert knowledge - if you had a view on potential vortex disruption / wave activity.

I feel we are on the cusp of a strong and significant SSW event, however not sure if this is one for this winter or whether the classic VI period will over write early destabilization of the vortex.

Be great to hear your thoughts 

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3 minutes ago, bluearmy said:

Apologies for not posting this gefs output - it’s consistent 

DF401DA5-74EB-41A5-84ED-A948624E7ABF.thumb.jpeg.fc9c508dac364d77a3ef282b23fea1de.jpeg

Lets hope its correct after reading Tamaras very sobering post in the model thread blue :)

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npst30.png

Down at 30 hpa the advance across N. America gets properly underway at +312 now so it has at last been drawing closer in range. The significant height response begins at +252 so that's encouraging. Won't be so encouraged if ECM/EPS don't show similar interest though!

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Obviously a long way to go, but if tonight's (24 Nov) ECM 12z NH 500hPa profile for 4th Dec verifies anything like the forecast, from an old study that undertook research into the Jan/Feb 1979 SSW, the combination of anomalous high pressure in both Atlantic and Pacific is not without interest??

Extract from the paper "How Well do we Understand the Dynamics of Stratospheric Warmings" by Michael E. McIntyre (page 56):

  • In the northern hemisphere winter the parts of the troposphere over the north Atlantic and Pacific act as separate resonant cavities, which can be excited independently of each other and of the stratosphere......
  • The stratosphere still responds as to a given forcing from below, and the stratospheric response (for a given state, of the stratosphere) will tend to be strongest in wave 1 when the Atlantic and Pacific anomalies happen to have opposite signs, and strongest in wave 2 when they happen to have the same sign.....  
  • If this version is a good approximation to the truth then there should be some tendency for the "strong wave 1" and "strong wave 2" conditions in the stratosphere to be mutually exclusive, especially at times when the magnitudes of the Atlantic and Pacific anomalies are at their largest.....
  • Such behaviour is indeed observed, and has often been remarked upon.

Tonight's ECM output:

500 hPa 5a187ce4b63dd_ECMNH500hpa24Novfor04Dec.thumb.png.d5bfe7060a2831458fa41eeba7244ae4.png Anomaly 5a187ceeb2b92_ECMNH500hpaanomaly24Novfor04Dec.thumb.png.3ba5d85655b56fc48205d45d00245bce.png

https://www.jstage.jst.go.jp/article/jmsj1965/60/1/60_1_37/_pdf

Edited by Blessed Weather
Link added.
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I believe this is the first true reversal forecasted this season. The GEFS supports this to some degree, but we all know the model has the tendency to be too progressive.

u_65N_10hpa.png

Edited by Ruben Amsterdam
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8 minutes ago, Ruben Amsterdam said:

I believe this is the first true reversal forecasted this season. The GEFS supports this to some degree, but we all know the model has the tendency to be too progressive.

u_65N_10hpa.png

Even if we dont get a reversal its still great to see zonal winds dropping as we move through Dec..

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12 minutes ago, northwestsnow said:

Even if we dont get a reversal its still great to see zonal winds dropping as we move through Dec..

We saw similar extraordinary 2 sigma drops last year being modeled (and almost verifying) only for the zonal winds to come back with a vengeance 

 

Oh and these winds are @ 65 degrees, not 60 where they need to reverse for a true ssw

Edited by ArHu3
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22 minutes ago, ArHu3 said:

Oh and these winds are @ 65 degrees, not 60 where they need to reverse for a true ssw

This is the WMO definition, yes. However, there is no real difference between using 60 and 65N when it comes to classifying SSW events. See: http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-13-00173.1

"Poleward of 60°N, the local and coherent reversal requirements yield nearly identical numbers of SSWs; anywhere in this region, if the wind reverses from westerly to easterly at one latitude, it is also almost certain that the wind is reversing everywhere poleward of that latitude."

This is also why Attard plots 65N and not 60N.

Edited by Ruben Amsterdam
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18 minutes ago, ArHu3 said:

We saw similar extraordinary 2 sigma drops last year being modeled (and almost verifying) only for the zonal winds to come back with a vengeance 

 

Oh and these winds are @ 65 degrees, not 60 where they need to reverse for a true ssw

I have a feeling this winter will be a little different to last year. 

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13 hours ago, Blessed Weather said:

Obviously a long way to go, but if tonight's (24 Nov) ECM 12z NH 500hPa profile for 4th Dec verifies anything like the forecast, from an old study that undertook research into the Jan/Feb 1979 SSW, the combination of anomalous high pressure in both Atlantic and Pacific is not without interest??

Extract from the paper "How Well do we Understand the Dynamics of Stratospheric Warmings" by Michael E. McIntyre (page 56):

  • In the northern hemisphere winter the parts of the troposphere over the north Atlantic and Pacific act as separate resonant cavities, which can be excited independently of each other and of the stratosphere......
  • The stratosphere still responds as to a given forcing from below, and the stratospheric response (for a given state, of the stratosphere) will tend to be strongest in wave 1 when the Atlantic and Pacific anomalies happen to have opposite signs, and strongest in wave 2 when they happen to have the same sign.....  
  • If this version is a good approximation to the truth then there should be some tendency for the "strong wave 1" and "strong wave 2" conditions in the stratosphere to be mutually exclusive, especially at times when the magnitudes of the Atlantic and Pacific anomalies are at their largest.....
  • Such behaviour is indeed observed, and has often been remarked upon.

Tonight's ECM output:

500 hPa 5a187ce4b63dd_ECMNH500hpa24Novfor04Dec.thumb.png.d5bfe7060a2831458fa41eeba7244ae4.png Anomaly 5a187ceeb2b92_ECMNH500hpaanomaly24Novfor04Dec.thumb.png.3ba5d85655b56fc48205d45d00245bce.png

https://www.jstage.jst.go.jp/article/jmsj1965/60/1/60_1_37/_pdf

Yes it is interesting and could lead to a more dramatic splitting of the vortex, as most famously in Jan 2009 - many reviews of that event have been published. However the high pressures typically need to be quasi-stationary and of a suitable duration and the corresponding Berlin wave 2 chart shows little activity by that time -

5a193436bce8b_ecmwfzm_ha2_f240171124.thumb.gif.614af2d92e91aa0effc338f2c5491213.gif

Pure wave 2 events are uncommon and the GFS/GEFS are forecasting a more typical wave 1 displacement at this point caused by high pressure from the Atlantic side. There are suggestions in the ensembles of a rapid downwelling through strat/trop coupling leading to increased pressure and heights over north America or north Pacific. This was something mooted last winter and subsequently tweeted by Andrea Lopez-Lang - see in the animation the stratospheric geopotential anomalies are initially linked to those around longitude 0°W then downwell around 120-180°W

 

Edited by Interitus
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11 hours ago, Interitus said:

5a192243e8abb_NH_HGT_10mb_38417121100.thumb.gif.b9c53a92fe14ba288b02503920bff188.gif

GFS unsurprisingly less extreme since this run but for interest's sake, this was a 60°N reversal, u = -0.2 m/s

17112500u384.thumb.png.eafc917bcb5fc75051b546bc0f2d34cd.png

Would be the 'classic' Canadian warming.

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