Stratosphere and Polar Vortex Watch

[Allseasons-Si]

Nowt to worry!!!

reinforcements are on there way

[Mike Poole]

3 hours ago, Gael_Force said:

I wondered about the resolution as there is so much more definition in the FV3 compared to current GFS. CF the +240 hour charts from current run.

     

 

FV3 is 13 km horizontal resolution out to day 16, but I don't think that is responsible for the niggles on the output, I think that is the plotting isn't used to the different data set on Meteociel and other sites, could be wrong.

[kold weather]

5 hours ago, Singularity said:

As far as I can see, GFS is pretty isolated in having the reversal completely fail to propagate downward, with the NAM actually going more positive in the lower stratosphere.

GOES-5 for example has a steady downward propagation and no +NAM development at all.

I've seen little evidence to justify taking GFS over other modelling strat-wise. Less sure about FV3 though; it would be a strange move if it didn't have the stratosphere resolution brought up to par with the likes of ECM.

In all fairness the last few runs look somewhat more realistic in terms of keeping the PV fragmented. It tries to reform on the 18z but is once again nearly split by the end of the run.

[ArHu3]

12 hours ago, Gael_Force said:

I wondered about the resolution as there is so much more definition in the FV3 compared to current GFS. CF the +240 hour charts from current run.

     

 

Probably a meteociel issue, if you go back into the gfs archives around 2011-2012 the Strat looks like that too

[Blessed Weather]

On 24/12/2018 at 15:10, sebastiaan1973 said:

But are there are the consequences of the lower heatflux at 100 hPa? Don't we need enhanced upward planetary wave propagation at 100 hPa - 300 hPa? for downwelling purposes.

Hi Sebastiaan. Sorry for the delay responding. Yes, I agree. Below is a simple explanation of the importance of continued upward wave activity in bringing about successful downward propagation of the SSW reversed (easterly) zonal winds into the troposphere.

I thought Amy's tweet was an interesting insight into this SSW and a pointer to why downward propagation of easterlies appeared to be stalling around 100 hpa.  

How does it move down through the atmosphere?

As it turns out, waves can only move around the Earth's atmosphere in westerly winds. Fluctuations in our weather send waves up through the atmosphere to the easterly winds in the stratosphere, where they travel no further, and instead break and reinforce the easterly winds, bringing the easterlies lower. This pattern continues until the easterlies have moved down to the troposphere - the lowest part of the atmosphere where our weather is.

It can take anything from a few days to a few weeks for this process to take place. 

Source Met Office: https://www.metoffice.gov.uk/learning/wind/sudden-stratospheric-warming             

[Summer Sun]

 

[karyo]

10 minutes ago, Summer Sun said:

 

To prevent mass hysteria or even suicide, please don't post this on the Hunt for cold thread. 

[Summer Sun]

 

[Interitus]

2 hours ago, Blessed Weather said:

Hi Sebastiaan. Sorry for the delay responding. Yes, I agree. Below is a simple explanation of the importance of continued upward wave activity in bringing about successful downward propagation of the SSW reversed (easterly) zonal winds into the troposphere.

I thought Amy's tweet was an interesting insight into this SSW and a pointer to why downward propagation of easterlies appeared to be stalling around 100 hpa.  

How does it move down through the atmosphere?

As it turns out, waves can only move around the Earth's atmosphere in westerly winds. Fluctuations in our weather send waves up through the atmosphere to the easterly winds in the stratosphere, where they travel no further, and instead break and reinforce the easterly winds, bringing the easterlies lower. This pattern continues until the easterlies have moved down to the troposphere - the lowest part of the atmosphere where our weather is.

It can take anything from a few days to a few weeks for this process to take place. 

Source Met Office: https://www.metoffice.gov.uk/learning/wind/sudden-stratospheric-warming             

It is simplified - the need for westerly winds is for the vertical propagation of planetary waves (and then not too strong which limits propagation also as seen during the middle of the SH winter). The mean easterly wind field at 10 hPa for example doesn't tend to descend en masse through the strat into the troposphere at 60°N. At 150 hPa the mean zonal wind very rarely becomes easterly during winter, and then only marginally -

In the MERRA data it has done so in the 45 days following SSW on 3 occasions and on one of those it had already been easterly in the days preceding the SSW.

The zonal flow anomalies represent perturbation of mean flow which tends to be regionalised i.e. through the geopotential height field of the waves and associated geostrophic wind, and when the perturbations become well aligned then the zonal wind anomalies can appear to descend, but also ascend of course.

 

 

Edited December 28, 2018 by Interitus

[northwestsnow]

Beginning to sound like this SSW is going to be chocolate tea pot material for cold for us anytime soon, if it all.

Wondering if any hope is going to be MJO related..

[fujita5]

17 minutes ago, karyo said:

To prevent mass hysteria or even suicide, please don't post this on the Hunt for cold thread. 

However you can see from the charts posted that zonal winds do decrease significantly north of 50N at all levels.  This, as far as my limited understanding can surmise, should allow slow moving ridge/trough configurations to develop with reasonable chances for amplification.  It certainly wouldn't usher in raging easterlies but we'd still be in with a chance of cold weather at times.

[Northern Sky]

2 minutes ago, fujita5 said:

However you can see from the charts posted that zonal winds do decrease significantly north of 50N at all levels.  This, as far as my limited understanding can surmise, should allow slow moving ridge/trough configurations to develop with reasonable chances for amplification.  It certainly wouldn't usher in raging easterlies but we'd still be in with a chance of cold weather at times.

Wait, what? Surely it's either going to be absolutely incredible, fantastic raging cold or desperate, horrendous, endless mild? We live in a world where there is only two possible outcomes to anything...

...don't we?

[fujita5]

1 minute ago, Northern Sky said:

Wait, what? Surely it's either going to be absolutely incredible, fantastic raging cold or desperate, horrendous, endless mild? We live in a world where there is only two possible outcomes to anything...

...don't we?

You forgot option 3: "Meh".  Cool, cloudy and completely uneventful. 

I'm hoping we get some clarity soon, it's becoming quite painful watching the clock tick down to when the warming event ends with no definitive answer on whether the easterlies reach the trop.

 

[Summer Sun]

 

[Summer Sun]

 

[Selliso]

2 minutes ago, northwestsnow said:

Beginning to sound like this SSW is going to be chocolate tea pot material for cold for us anytime soon, if it all.

Wondering if any hope is going to be MJO related..

We're not seeing the "usual" type of response down into the trop of recent years, that's for sure... Loving the model watching, though. I want the cold as much as the next person, but the model conflict is half the fun!  

I am still 100% on the fence, and probably will be until 1st Jan. 

[bluearmy]

45 minutes ago, fujita5 said:

However you can see from the charts posted that zonal winds do decrease significantly north of 50N at all levels.  This, as far as my limited understanding can surmise, should allow slow moving ridge/trough configurations to develop with reasonable chances for amplification.  It certainly wouldn't usher in raging easterlies but we'd still be in with a chance of cold weather at times.

If only we could have an MJO in phase 7 or 8 to take advantage of this ...........

[Interitus]

1 hour ago, Interitus said:

The zonal flow anomalies represent perturbation of mean flow which tends to be regionalised i.e. through the geopotential height field of the waves and associated geostrophic wind, and when the perturbations become well aligned then the zonal wind anomalies can appear to descend, but also ascend of course.

 

Ok, an illustration. The last couple of GFS runs have toyed with a double dip reversal at 10 mb, here are the forecast zonal winds at 10, 100 and 500 mb from today's 06z -

The first strong reversal has virtually no effect at 100 mb, and the 500 mb level shows typical variability. Looking at the geopotential anomalies for the maximum reversal on Jan 4th shows that there are some similar features but they aren't particularly well aligned at each level -

At the second dip though there is a following reduction in zonal wind at 100 and 500 mb as the geopotential anomalies are more closely aligned -

 

 

[Singularity]

 

Tentative I know, but maybe GFS is finally starting a move toward a better-defined wave-2 pattern and Canadian vortex which, from what I've read lately, should be more conducive to downward propagation of the reversal.

[chris55]

Lots of conflicting views regarding the strat downwelling or not. I have a feeling we are in slightly uncharted territory with the anomalies surround the SSW, so should be fascinating watching how this unfolds over the coming month. 

[chris55]

A good little snippet from Liam Dutton regarding the possible effects of the SSW. 

For any stat newbies this is a good guide to what might happen with this SSW.

Edited December 28, 2018 by chris55

[Summer Sun]

 

[Catacol]

Wave 2 impacts ongoing through to day 10 and apparently building at this point

10hpa winds now set to bottom out at around -16m/s around 3rd/4th Jan

with the majority of GFS members showing ongoing reversal over 10 days or more. Downward propagation of easterly components in question now - good tweet from Amy Butler earlier showing disagreement between GFS and GEOS on extent of that propagation....and she refused to be drawn on which was more likely to verify....but overall the longer the circulation at 10hpa remains in reverse and under ongoing stress the better it has to be on chances of successful downward propagation. 

Out at 10 days ECM sees a distressed vortex in the lower strat with the stronger daughter stretched across Asia with definite potential for height rises around Greenland

Much hangs on the extent to which the lower strat can couple to the trop...but simultaneous movement of MJO through towards 7-8-1 orbit ought to provide trop based guidance for the Greenland ridge to form. If the TPV manages to resist impacts from both above and below it will be doing well indeed....

Edited December 28, 2018 by Catacol

[Interitus]

7 minutes ago, Catacol said:

10hpa winds now set to bottom out at around -16m/s around 3rd/4th Jan

At 65°N - the GFS forecasts since 23/12 18z (last without SSW) for 60°N have been 

-3.4, -0.4, -3.6, -14.3, -13.4, -5.9, -9.2, -11.3, -6.5, -8.1, -11.4, -13.5, -10, -10.9, -10.7, -11.3, -11.9 and -11.2 m/s (up to today's 06z) 

Notably stronger than the FV3 which since 24/18 18z (last seen without SSW - missed a few runs) -

-2.6, -, -, -6.1, -3.8, -4.3, -, -6.3, -9.5, -7.9, -7.7, -7.6, -5.4, -7.1 (to 06z today) 

 

[Catacol]

9 minutes ago, Interitus said:

At 65°N - the GFS forecasts since 23/12 18z (last without SSW) for 60°N have been 

-3.4, -0.4, -3.6, -14.3, -13.4, -5.9, -9.2, -11.3, -6.5, -8.1, -11.4, -13.5, -10, -10.9, -10.7, -11.3, -11.9 and -11.2 m/s (up to today's 06z) 

Notably stronger than the FV3 which since 24/18 18z (last seen without SSW - missed a few runs) -

-2.6, -, -, -6.1, -3.8, -4.3, -, -6.3, -9.5, -7.9, -7.7, -7.6, -5.4, -7.1 (to 06z today) 

 

Yes. Is 65 degrees not more significant?

Edited December 28, 2018 by Catacol