Stratosphere and Polar Vortex Watch

[karyo]

Interesting read Sebastian. However the coming season looks like enso neutral as things stand now.

[feb1991blizzard]

4 minutes ago, karyo said:

Interesting read Sebastian. However the coming season looks like enso neutral as things stand now.

I am never too worried about enso neutral TBH, far rather have that than too strong a signal like +/- 2.0c, which will pretty much kill off your chances of a cold UK winter apart from right at the end feb into March, 1986,1991 and 1994 all were ENSO neutral and had potent February Easterlies.

[sebastiaan1973]

The key findings are as follows.

1.

ENSO produces a hemispheric negative NAM pattern, which is considerably stronger in the Atlantic sector in late winter. The ENSO response in the Atlantic is mediated by planetary wave forcing of the stratosphere/upper troposphere (Huang et al., 1998; Ineson and Scaife, 2009). Our results suggest that there is a lag in the response in the Atlantic sector relative to the direct tropospheric forcing in the North Pacific, which is quite similar in the different QBO phases and in both early/mid- and late winter. QBO modulates the ENSO signal so that it becomes significant in the Atlantic sector already in early/mid-winter. The ENSO effect in the easterly QBO phase resembles a negative NAO pattern. The weaker polar vortex during the easterly QBO (Holton and Tan, 1980; Maliniemi et al., 2016) advances the mediation of a negative NAO signal to the Atlantic sector (Ineson and Scaife, 2009) and is observed earlier than without QBO modulation. In late winter when the Holton-Tan mechanism is no longer significant (Lu et al., 2014; Maliniemi et al., 2016) a negative NAO signal is rather similar in the two QBO phases. This QBO modulation of ENSO teleconnection to the Atlantic sector verifies the modeling study by Calvo et al. (2009), both in early/mid- and late winter.

2.

The typical positive NAO pattern related to volcanic activity becomes more clear in the westerly QBO phase, especially in late winter. We suggest that this is due to the weaker Brewer-Dobson circulation in the westerly QBO (Flury et al., 2013), which mixes volcanic aerosols less effectively, leaving them mainly to the lower equatorial stratosphere. This would lead to a stronger infrared absorption by these aerosols in the lower equatorial stratosphere, to larger equator-to-pole temperature gradients and a stronger polar vortex (Robock, 2000; Otterå et al., 2010).

3.

The geomagnetic activity (energetic particle precipitation) signature in both early/mid- and late winter is modulated by the QBO phase. Geomagnetic activity produces a significant circulation pattern mainly during the easterly QBO. It represents a dipole pressure pattern similar to the positive NAO pattern, although in late winter it is shifted towards the pole. The geomagnetic activity signal is now verified by a simultaneous consideration of sunspot effects, thus generalizing the earlier studies (Maliniemi et al., 2013, 2016; Roy et al., 2016). A possible explanation to the QBO dependence of the signal to geomagnetic activity is that the Brewer-Dobson circulation is stronger in easterly QBO (Flury et al., 2013). This enhances the transport of ozone to high latitudes (Li and Tung, 2014) and the downwelling of NOx (produced by particle precipitation (Funke et al., 2014)) inside the polar vortex (Baldwin et al., 2001). This would lead to a larger ozone loss for a given level of geomagnetic activity in the QBO easterly phase compared to the westerly QBO, and as so to stronger polar vortex due to the stratospheric cooling (Baumgaertner et al., 2011).

4.

The pattern of the signal due to sunspots (or any other solar driver like TSI or EUV/UV co-varying with sunspots) is very different between early/mid- and late winter. The positive NAO pattern due to SSN in late winter, which is mainly obtained in the easterly QBO phase (in agreement with, e.g., Labitzke and van Loon, 1988; Lu et al., 2009), suggests for the top-down mechanism originating in the stratosphere by enhanced solar UV heating (Kodera and Kuroda, 2002). On the other hand, the positive SLP signature in Aleutian in early winter is only marginally modulated by the QBO, which suggests that the stratospheric variability does not have an effect on it. Rather, it supports the bottom-up mechanism, which is directly forced from the troposphere by enhanced heating in the tropical Pacific (e.g., Meehl et al., 2008). These results related to sunspot activity during early/mid- and late winter in different regions and in different QBO phases verify the different earlier findings (Gray et al., 2010, and multiple references therein) under a common global setting.

https://www.sciencedirect.com/science/article/pii/S1364682618301421

[sebastiaan1973]

https://www.metoffice.gov.uk/research/climate/seasonal-to-decadal/gpc-outlooks/ens-mean

Intrestring update from Glosea5. Neutral ENSO. And high Area in northern Europe.

[weirpig]

50 minutes ago, sebastiaan1973 said:

https://www.metoffice.gov.uk/research/climate/seasonal-to-decadal/gpc-outlooks/ens-mean

Intrestring update from Glosea5. Neutral ENSO. And high Area in northern Europe.

MMM  a very long  way out   but could show perhaps   a more easterly element as we approach the fun season?. 

[JeffC]

1 hour ago, weirpig said:

MMM  a very long  way out   but could show perhaps   a more easterly element as we approach the fun season?. 

I thought that!

[ItNeverSnowsInWindsor]

We have a 20-40% chance of below average temperatures! Lower heights over S Europe also depicted as a -NAO looks more promising!

Edited August 12, 2019 by prolongedSnowLover

[Cheshire Freeze]

13 hours ago, sebastiaan1973 said:

https://www.metoffice.gov.uk/research/climate/seasonal-to-decadal/gpc-outlooks/ens-mean

Intrestring update from Glosea5. Neutral ENSO. And high Area in northern Europe.

A very good update but nothing to put any stock in at this range. Interesting to see what looks like a potential retrogressive signal with the jet heading underneath the blocking. 

Generally, indications look very good to me at this very early juncture.

[northwestsnow]

7 hours ago, CreweCold said:

A very good update but nothing to put any stock in at this range. Interesting to see what looks like a potential retrogressive signal with the jet heading underneath the blocking. 

Generally, indications look very good to me at this very early juncture.

Yes i agree C C..

Added to this we have a favourable SST profile in the Atlantic, which in my opinion scuppered last winter.

Early days but as long as ENSO doesn't go crazy i think this winter holds a decent chance of being seasonal..

[summer blizzard]

Does anybody have the SSW dates from 1979 onward.

 

 

 

 

[Kirkcaldy Weather]

5 minutes ago, summer blizzard said:

Does anybody have the SSW dates from 1979 onward.

 

 

 

 

https://www.researchgate.net/figure/List-of-the-Major-SSW-Events-Recorded-Between-1958-and-2013-Peak-lunar-tidal-Peak-ZMZW_tbl1_324608809/amp

http://birner.atmos.colostate.edu/ssw.html

[JeffC]

Any chance we could update the title? I get it that we might want to just let the thread run for historic purposes!

[SMU]

Vortex now nearly 2M/S behind the record-

[JeffC]

3 hours ago, Kirkcaldy Weather said:

https://www.researchgate.net/figure/List-of-the-Major-SSW-Events-Recorded-Between-1958-and-2013-Peak-lunar-tidal-Peak-ZMZW_tbl1_324608809/amp

http://birner.atmos.colostate.edu/ssw.html

Amazing there wasn't one for 6 years between 73 and 79!!

[JeffC]

2 hours ago, Steve Murr said:

Vortex now nearly 2M/S behind the record-

Crikey, wonder what the explanation of that is?

Edited August 18, 2019 by JeffC

[SMU]

20 hours ago, JeffC said:

Crikey, wonder what the explanation of that is?

A Very warm lower stratosphere more than likely-

The pattern now becoming more defined outside of climatology ( note the blue line is 2019/20 its about 2 M/S below the baseline )

The only caveat here is that its August not November so there is time for it to recover-

& for all those enjoying the daily blocked CFS runs for the Winter - its because the model is keeping the vortex @sub 20M/S where as the climo norm is nearer 40M/S in December ...

Also look at the clustering below climo at around 10 M/S

Edited August 19, 2019 by Steve Murr

[JeffC]

3 minutes ago, Steve Murr said:

A Very warm lower stratosphere more than likely-

The pattern now becoming more defined outside of climatology ( note the blue line is 2019/20 its about 2 M/S below the baseline )

The only caveat here is that its August not November so there is time for it to recover-

& for all those enjoying the daily blocked CFS runs for the Winter - its because the model is keeping the vortex @sub 20M/S where as the climo norm is nearer 40M/S in December ...

agreed there's time for it to recover, but rate and extent of recovery will be dependent upon lower strat temp also going into winter? which may be influenced by Hurricane activity - i.e. deposition of above ave temp air into the higher latitudes? So maybe we need a few Norhbound hurricanes to perpetuate things...or maybe not!  

[Singularity]

It's going to be really interesting - and educational - to see how the unusually warm lower stratosphere interacts with the colder than usual upper levels.

It may depend a lot on the tropospheric NAM state (i.e. AO state). The more negative it tends to stay, the less wave activity flux will be able to reinforce the lower stratospheric positive temp & height anomalies, and vice versa. 

I wonder whether all the anomalous heat and moisture from the unusal amounts of open Arctic Ocean waters will drive enough extra rising motion, as the upper atmosphere seasonally cools, to force some +AO periods even with the warm lower stratosphere in place. IIRC, we saw a fair bit of that in 2016, with the lower stratospheric zonal winds kept well below normal until Dec, when - of course - things turned on their heads just when we least wanted them to.

That year, it felt like we came very close to the first Arctic sea ice loss-driven major HLB episode in the winter months (as opposed to autumn, in which we've seen a few, but mostly not of the cold variety for the UK). Take an even more disrupted lower stratospheric vortex this year, plus a descending E QBO and low solar activity, and who knows what might unfold...

[weirpig]

Just looking at the Vortex and the strength the CFS forcasts it to be during the winter months  i was wondering is this something a model can predict with a degree of certainty   ( however low that may be at such a lead time)  or is start forcasts still very much hit and miss?.  Because obviously if the CFS is correct  a cold one could very well be on the way . 

[sebastiaan1973]

2 hours ago, Singularity said:

That year, it felt like we came very close to the first Arctic sea ice loss-driven major HLB episode in the winter months

http://www.nature.com/articles/s41558-019-0551-4.epdf?author_access_token=lev7cCLvJaqZgqEL2fkrCtRgN0jAjWel9jnR3ZoTv0OkPw7OWz-ctumf1Sllaa-sNqBW8kixcwl-ojSoyKUmUfvHbXmZ3llXRmZN-HO_pmKRWEHLwCuZqZkuv4bolog-ehQV4R4jg8i93P7ntZX4_w%3D%3D

Observations show that reduced regional sea-ice cover is coincident with cold mid-latitude winters on interannual timescales.

However, it remains unclear whether these observed links are causal, and model experiments suggest that they might not be.

Here we apply two independent approaches to infer causality from observations and climate models and to reconcile these

sources of data. Models capture the observed correlations between reduced sea ice and cold mid-latitude winters, but only

when reduced sea ice coincides with anomalous heat transfer from the atmosphere to the ocean, implying that the atmosphere

is driving the loss. Causal inference from the physics-based approach is corroborated by a lead–lag analysis, showing that

circulation-driven temperature anomalies precede, but do not follow, reduced sea ice. Furthermore, no mid-latitude cooling is

found in modelling experiments with imposed future sea-ice loss. Our results show robust support for anomalous atmospheric

circulation simultaneously driving cold mid-latitude winters and mild Arctic conditions, and reduced sea ice having a minimal

influence on severe mid-latitude winters.

Edited August 20, 2019 by sebastiaan1973

[bluearmy]

On 13/08/2019 at 02:06, CreweCold said:

A very good update but nothing to put any stock in at this range. Interesting to see what looks like a potential retrogressive signal with the jet heading underneath the blocking. 

Generally, indications look very good to me at this very early juncture.

would want to see the trend on that Aaron ......could easily take a mean sceuro block from that glosea output which doesn’t deliver winter to nw Europe ....if the trend is retrogressive then we could take further interest ..... that’s a sizeable high anomoly although our best extended wintry periods do tend to come from weak blocking in the rough area glosea shows as the jet travels into Biscay 

the coldies are looking for as many background signals to line up so that a few jumping ship late on doesn’t deliver another season of disappointment against expectation. 

[Interitus]

Bit of a nonsense calling it a weaker than average vortex, the vortex hasn't reformed yet.

[mb018538]

8 minutes ago, Interitus said:

Bit of a nonsense calling it a weaker than average vortex, the vortex hasn't reformed yet.

Yeah i don't get the incessant obsession with it at this stage of the year either. It hasn't formed, and it doesn't really matter if it's a bit below normal speed. It can quickly spin up to normal and above normal in a short space of time, which renders all of this irrelevant.

[mountain shadow]

19 hours ago, Interitus said:

Bit of a nonsense calling it a weaker than average vortex, the vortex hasn't reformed yet.

I think the point is, that the weaker the polar stratosphere is now that it might take longer to deepen as we move through Autumn and into Winter there by potentially improving the probability of a colder start to Winter than normal.

[karyo]

17 minutes ago, mountain shadow said:

I think the point is, that the weaker the polar stratosphere is now that it might take longer to deepen as we move through Autumn and into Winter there by potentially improving the probability of a colder start to Winter than normal.

We have seen those slow starts before, the vortex can remain weak for a couple of months and then quickly pick up speed in November. It may lead to a more blocked autumn but the way global temperatures are going (and shortage of ice) it is more likely to result in residual warmth than any notable cold.