Stratosphere and Polar Vortex Watch 2020

[snowy weather]

Just now, Allseasons-si said:

Yes this is possible as we would not know yet where the pv segments would end up in the lower latitudes but a greater chance than without an SSW.

Thank you. Can the cold weather from an ssw end up in both the UK and US or can it only end up in one place?

 

[sundog]

6 minutes ago, snowy weather said:

Is it possible for us to be on the wrong side of a SSW? 

For example can it happen that instead of the UK, it is the US that gets all the cold due to the SSW?

 

I think that's what happened the last time in 2019.

[Allseasons-Si]

1 minute ago, snowy weather said:

Thank you. Can the cold weather from an ssw end up in both the UK and US or can it only end up in one place?

 

A displacement(i think) would be two places at opposite ends but a split can be more places,it really is hard to judge and we would have more info nearer the time,besides,i am not one to be asking as i don't have as much knowledge as the more strat geeks on here(sorry guys)

 

[snowy weather]

Just now, Allseasons-si said:

A displacement(i think) would be two places at opposite ends but a split can be more places,it really is hard to judge and we would have more info nearer the time,besides,i am not one to be asking as i don't have as much knowledge as the more strat geeks on here(sorry guys)

 

Thank you, much appreciated:)

[mb018538]

That's some upward spike there!

[bluearmy]

9 minutes ago, mb018538 said:

That's some upward spike there!

Give it a few runs to see some continuity - the 00z run later on looks very mobile in the mid/upper strat. Last couple  gfs runs have actually pretty much removed the reverse flow right across the strat later on. (Away from the tropics of course) 

[ALL ABOARD]

8 minutes ago, bluearmy said:

Give it a few runs to see some continuity - the 00z run later on looks very mobile in the mid/upper strat. Last couple  gfs runs have actually pretty much removed the reverse flow right across the strat later on. (Away from the tropics of course) 

Was looking promising for a long reversal and another warming for a split.. 

Wonder what's driving the rapid recovery. 

[keithlucky]

7 minutes ago, bluearmy said:

Give it a few runs to see some continuity - the 00z run later on looks very mobile in the mid/upper strat. Last couple  gfs runs have actually pretty much removed the reverse flow right across the strat later on. (Away from the tropics of course) 

Looks like stratospheric warning underway big drop in south Greenland  and Iceland  temperatures forecasted for Thursday onwards,

[sebastiaan1973]

Oops. The downwelling of GFS  stagnates.

[SqueakheartLW]

At no stage did the ECM predict a reversal at 1hpa getting to -48 m/s yesterday and predicted to be -46 m/s today. Both big upgrades on the initial ECM predictions

These are how the actual 1hpa figures look compared with the predicted figures from up to 10 days ago

Prediction Date     3rd January     4th January

25th December     -8.3 m/s           -23 m/s

26th December     -27 m/s            -34 m/s

27th December     -23 m/s            -31 m/s

28th December     -21 m/s            -31 m/s

29th December     -21 m/s            -30 m/s

30th December     -27 m/s            -33 m/s

31st December     -32 m/s            -33 m/s

1st January            -40 m/s            -38 m/s

2nd January          -41 m/s            -41 m/s

3rd January          -48 m/s             -46 m/s

Back on Christmas Day the ECM only predicted -8.3 m/s for 3rd January. Much less than what we actually ended up with. It also went with -23 m/s for the 4th (Today) and the 3rd January prediction is -46 m/s. We shall find out tomorrow which was closest to the actual figure

 

 

Edited January 4, 2021 by SqueakheartLW

[bluearmy]

just an observation ...... the gfs strat runs are now looking like maintaining the displacement after a brief split (similar to the one we have now which showed a v brief split ).  I wonder if this is due to the current change in the trop patterns being modelled over the last  day or so ?  different trop waves being shoved up into the strat compared to the models runs of a few days ago will result in different effects in the upper strat in the week or so to come thereafter ????

 

[Battleground Snow]

This is positive right? Glosea seeing the 2nd warming? Albeit out of date data now?

 

[ALL ABOARD]

1 minute ago, Battleground Snow said:

This is positive right? Glosea seeing the 2nd warming? Albeit out of date data now?

 

You'd think so but then

 

[knocker]

An extract from Stratosphere Troposphere Interactions by K. Mohanakumar

4.12.1 Evolution of Warming

During the prewarming stage an intense polar night jet stream with strong vertical wind shear will appear. Al this time a blocking situation develops in the troposphere. There is amplification of wave numbers I and 2 occurring in the upper troposphere and lower Stratosphere. There are two types (Type A and Type B) of wave amplification which takes place during the prewarming period. In Type A, intensification of wave number 2 occurs about 2 weeks prior to the onset of the major warming. This is closely followed by an increase in the amplitude of wave number I with a subsequent weakening of wave number 2. During this time. wave number I reaches a peak about I week prior to the warming. In Type B warming, wave number I maintains a large amplitude for a long period. Type A is the most frequently occurring type of stratospheric warming.

An important character of sudden warming is its downward propagation from 45 km into the lower stratosphere. This feature is not zonal in character. but has nonzonal structure. with a planetary wave tilting westward with height. In the middle latitudes. warming in the stratosphere (40 km) is followed by cooling in the mesosphere (65 km). Simultaneously, the opposite occurs in low latitudes, with stratospheric cooling and mesospheric warming, but the magnitude of the changes in the lower latitudes is one order less compared to that noted in higher latitudes.

4.12.2 Theory of Stratospheric Warming

Sudden stratospheric warming evolves in the darkness of the polar night without any apparent external source of beating. However, in a major warming event, the mean temperature of the stratosphere increases at the rate of I 0-C per day and within a week. the normal north-south temperature gradient gets reversed. It is believed that this occurs mainly due to the convergence of heat and momentum fluxes associated with the amplified transient planetary-scale waves. This again produces an induced meridional circulation which decelerates the westerly jet.

Earlier researchers were deceived by the apparent downward propagation of the warming and easterlies and looked for an upper energy source. Further studies, like that of Matsuo (1971), have shown that the source of energy lies in the troposphere. In this theory It is explained that a sudden increase in stationary planetary wave amplitude m the troposphere is accompanied by vertical propagation of transient wave energy into the stratosphere.

The transient wave energy passes through the stratosphere without any absorption, but gets trapped in the mesosphere causing convergence of heat and easterly momentum. Due to lower density in the upper levels, the effect on temperature and wind becomes substantial. The prewarming temperature gradient becomes weak and gets reversed. The westerly jet weakens and may be replaced by easterly winds.

The appearance of the easterly flow above the westerly flow produces a critical level with zero wind velocity in the mean current, where the horizontal speed of the mean current is equal to the horizontal phase speed of stationary waves in the troposphere. The easterly regime descends as the westerly wind gets destroyed. The critical level of wave energy thus comes down. The processes of energy absorption and sequence of events may be so fast and mixed that the appearance of easterlies may look simultaneous throughout the stratosphere (Holton and Austin 1991).

The vertically rising wave energy from the troposphere is spread over a band of synoptic and planetary-scale waves. Since the stratosphere is opaque to synoptic scale waves, the transmissivity of the planetary-scale wave increases. As a result, wave numbers l and 2 are dominant in the upward propagation of wave energy from the troposphere into the stratosphere. It is believed that wave number l prepares conditions favorable for stratospheric sudden warming, whereas wave number 2 acts as an effective source of energy for the stratospheric warming.

Prior to the incidence of SSW, the stratosphere is so tuned that relatively small perturbation gets enormously amplified within a short period, a phenomenon called resonance. Association between the tropospheric blocking situation, amplification of standing planetary waves in the troposphere and lower stratosphere, and the subsequent appearance of sudden warming in the stratosphere is viewed as manifestation of the same phenomenon in the troposphere, stratosphere, and to a certain extent in the mesosphere. The difference among various situations lies in the differences in the depths of tuned conditions, favorable for resonance.

Since the energy source lies in the troposphere, tuning of the troposphere leads to resonance in the troposphere and the appearance of blocking situation. If the middle atmosphere also gets tuned at or around the time of resonance and blocking situation m the troposphere, then there is resonant response of the middle atmosphere also (Schberl 1978). This may be the reason why all stratospheric warmings are accompanied or preceded by the tropospheric blocking phenomenon, but all tropospheric blockings are not accompanied by SSW.

It is hypothesized that sudden increase in planetary wave amplitude in the troposphere during winter triggers vertically propagating transient wave energy. It can be considered that troposphere and middle atmosphere constitute one system tuned for the occurrence of resonance; the upward flux of wave energy from the upper troposphere into the lower stratosphere cannot be taken as a lower boundary condition for the stratospheric warming. Thus upward flux will have to be taken as an internal phenomenon for the troposphere-stratosphere-mesosphere system

[Paul_1978]

2 minutes ago, Battleground Snow said:

This is positive right? Glosea seeing the 2nd warming? Albeit out of date data now?

 

Second graph shows zonal winds going back westerly before end of Feb?

[Battleground Snow]

1 minute ago, ALL ABOARD said:

You'd think so but then

 

Let's hope it doesn't survive!

[Battleground Snow]

1 minute ago, Paul_1978 said:

Second graph shows zonal winds going back westerly before end of Feb?

I think it always would have this early in the season, the longer it's reversed the more chance of northern blocking can be established long term. Got to admit it's hard to keep up with this with the data changing so much. Guess it best just to watch and see how it plays out.

[Singularity]

A SSW that propagates down to the troposphere effectively places reduced or reversed zonal flow there which then takes time to be eroded from above once the polar vortex has recovered, which it usually does unless the SSW has occurred late in the season.

Sometimes the more meridional / amplified pattern permitted by the reduced or reversed zonal flow leads to further rounds of warming in the lower stratosphere which can lead to multiple periods of HLB, such as we saw in 2013.

The way forecasts are evolving, I'm getting the impression that we're going to be looking for a favourable displacement outcome - one which doesn't place the polar vortex above the North Atlantic. This is certainly possible. Tropospheric impacts will be weaker compared to a split event, so probably just a case of seeing whether the zonal flow is reduced enough for the subtropical high to gain a foothold somewhere in the Iceland to Scandinavia area.

Or at least throw up some 'wedges'.

[Vikos]

Well, hopefully we get that negatives (easterly) currents at 60°N/500-1000hpA in nearer future.

In the animatioan one can see that positive blob coming from 30°N, but than gets punched back by negatives... that's where my hopes lay, some milderlish days with a significant cold outcome. Models struggel, but ECM is a rock in predicting strat-trop couplings (imho)

We need to give a couple of days, and just to relay on the main runs 00z/12z wich have a higher resolution

 

GFS runs differences (example)

Real time data usage here -->

Metcheck.com - GFS GDAS Information - How much observation data went into this GFS run? Latest run and archive information

WWW.METCHECK.COM

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Metcheck.com - GFS GDAS Information - How much observation data went into this GFS run? Latest run and archive information. Updated every 6 hours.

 

Edited January 4, 2021 by Vikos

[Bullseye]

As for the initial warming happening around today/tomorrow, are we looking at a displacement of PV?

The reason I ask, was the JMA and GFSp not going for split of the PV within 5-day range (I am sure @SqueakheartLW mentioned this in earlier post few days back), if so would this not be concerning for the both models but especially GFSp - I could have picked this up wrong. Cheers

[mountain shadow]

17 minutes ago, Bullseye said:

As for the initial warming happening around today/tomorrow, are we looking at a displacement of PV?

The reason I ask, was the JMA and GFSp not going for split of the PV within 5-day range (I am sure @SqueakheartLW mentioned this in earlier post few days back), if so would this not be concerning for the both models but especially GFSp - I could have picked this up wrong. Cheers

ECM has a split at 10hpa.

 

[northwestsnow]

3 hours ago, sebastiaan1973 said:

Oops. The downwelling of GFS  stagnates.

You seem like the net weather grim reaper for coldies 

[chris55]

50 minutes ago, mountain shadow said:

ECM has a split at 10hpa.

 

Is that actually a split? Or a just a squash? I can see two centres but they are linked??

[bluearmy]

1 hour ago, Paul_1978 said:

Second graph shows zonal winds going back westerly before end of Feb?

Of course - it can’t stay easterly for too long in winter ——— this isn’t  ‘the day after tomorrow’.  Expect westerly to return approx 20th jan. hopefully they won’t become too strong

51 minutes ago, mountain shadow said:

ECM has a split at 10hpa.

 

Yes, it’s a displacement but there has always been a v short lived split preceding it. The much vaunted split in mid month looks like being another v temp split high up at 10 hpa and properly split in the mid strat  (50hpa)

[sebastiaan1973]

12 minutes ago, northwestsnow said:

You seem like the net weather grim reaper for coldies 

Sorry for the inconvenience