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Stratosphere and Polar Vortex Watch


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Some useful tropospheric developments upcoming which are likely to have stratospheric impacts towards the end of November and more particularly into December. A strong convectively coupled tropic

so after many days the GFS & FNMOC & canadian finally now follow the Euro with 44 out 64 Members with a split at day 9- The ECM is day 8. We will call it - SSW & Split for 1st Ja

For all that watch the zonal winds. Let me urge you to look at the geopotential heights more. At least as far as weakening/strengthening trends go. Because as the polar vortex cries for help, you migh

Posted Images

14 minutes ago, Yarmy said:

 

NDJ

convert_image-gorax-green-002-6fe5cac1a3

DJF

convert_image-gorax-green-000-6fe5cac1a3

 

If you're being really picky, DJF could use a negative height anomaly over western Russia, but...

 

What a lovely update that is.  got a hunch this year some may see a white festive period. 

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10 hours ago, Yarmy said:

 

NDJ

convert_image-gorax-green-002-6fe5cac1a3

DJF

convert_image-gorax-green-000-6fe5cac1a3

 

If you're being really picky, DJF could use a negative height anomaly over western Russia, but...

 

We've been here before with that model. 2 years back I think. In the end although we were kind of blocked, we couldn't get any troughing to our S or over Europe. 

Pinch of salt. 

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8 hours ago, CreweCold said:

We've been here before with that model. 2 years back I think. In the end although we were kind of blocked, we couldn't get any troughing to our S or over Europe. 

Pinch of salt. 

Absolutely, and it's different enough from last month's update to not take too seriously yet, albeit that had a fairly substantial +ve anomaly over the polar regions too. 

Edit: The model was also upgraded last November from the old System 4 to the SEAS5. 

Edited by Yarmy
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The z500 geopotential anomaly charts are distorted by the fact that geopotential heights are proportional to temperature - with a warmer arctic there is a positive anomaly. Better to use sea level pressure - probably shows what many people want to see with regards near surface flow but the anomalies are not particularly dramatic -

convert_image-gorax-green-009-6fe5cac1a363ec1525f54343b6cc9fd8-Ifduu2.png

 With regard to the stratosphere, it may have potential for wave 1 propagation from the eurasian side to the stratospheric Aleutian high giving strat vortex displacement.

Just to add, looking at the earlier charts in the past year this completely missed the SSW influenced cold early spring and the warm summer.

Edited by Interitus
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Certainly looks like another interesting winter ahead. 

Is the jury still out on the anomalous QBO reversal of 15/16? The last I remember reading about it, was that it was felt to be primarily ENSO driven with mid lat Rossby wave interference. But still with many more questions than answers lingering.

 

 

Edited by s4lancia
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Just saw a tweet from yesterday showing CFSV2 forecast for first week October has an anomously weak westerly flow at 10mb ……. now this is the CFSV2 but stuck clocks are right twice a day and we aren't talking too far ahead in any case …...analogues with 2009 would I think tie in with a very weak zonal flow at the beginning of the season

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1 hour ago, bluearmy said:

Just saw a tweet from yesterday showing CFSV2 forecast for first week October has an anomously weak westerly flow at 10mb ……. now this is the CFSV2 but stuck clocks are right twice a day and we aren't talking too far ahead in any case …...analogues with 2009 would I think tie in with a very weak zonal flow at the beginning of the season

Interesting.  Another reference to 2009/10.  I know it's early days but for the last few weeks when I've been asked about winter by colleagues at work I've given something like 2009/10 as my best guess.  ENSO similar but maybe we're weaker this year, and weak polar vortex - it will be really interesting to watch the evolution of the vortex over the next couple of months, to see if a front loaded winter actually occurs.  If the rest of 2018 is anything to go by an interesting December would not surprise!

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1 hour ago, sebastiaan1973 said:

Sorry to say but in 2009/2010 we had a moderate tot strong El Nino. 

http://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php

QBO-phase strongly negative in 2009/2010. http://www.esrl.noaa.gov/psd/data/correlation/qbo.data

Yes, you are correct.  Sorry, my post above was not particularly well worded, Nino but weaker than 2009/10 was all I meant re ENSO. 

I wasn't claiming 2009/10 is an analogue for this year, it is more a gut feeling - from all the models, data and opinions I've looked at so far - that I think (at the moment) come winter the actual weather will pan out similar to 2009/10.  Time will tell!

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9 hours ago, Mike Poole said:

Yes, you are correct.  Sorry, my post above was not particularly well worded, Nino but weaker than 2009/10 was all I meant re ENSO. 

I wasn't claiming 2009/10 is an analogue for this year, it is more a gut feeling - from all the models, data and opinions I've looked at so far - that I think (at the moment) come winter the actual weather will pan out similar to 2009/10.  Time will tell!

Seasonal models are generally useless.

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1 minute ago, summer blizzard said:

Seasonal models are generally useless.

And I still think taking into account models, real data and opinions that I have read including yours, that weather patterns this winter will follow a 2009/10 trend.  If I'm wrong please judge me after the event.

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On 21/09/2018 at 21:22, summer blizzard said:

Seasonal models are generally useless.

We make some progress: https://journals.ametsoc.org/doi/10.1175/JCLI-D-16-0153.1

Significant predictive skill for the mean winter North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) has been recently reported for a number of different seasonal forecasting systems. These findings are important in exploring the predictability of the natural system, but they are also important from a socioeconomic point of view, since the ability to predict the wintertime atmospheric circulation anomalies over the North Atlantic well ahead in time will have significant benefits for North American and European countries.

In contrast to the tropics, for the mid latitudes the predictive skill of many forecasting systems at the seasonal time scale has been shown to be low to moderate. The recent findings are promising in this regard, suggesting that better forecasts are possible, provided that key components of the climate system are initialized realistically and the coupled models are able to simulate adequately the dominant processes and teleconnections associated with low-frequency variability. It is shown that a multisystem approach has unprecedented high predictive skill for the NAO and AO, probably largely due to increasing the ensemble size and partly due to increasing model diversity.

Predicting successfully the winter mean NAO does not ensure that the respective climate anomalies are also well predicted. The NAO has a strong impact on Europe and North America, yet it only explains part of the interannual and low-frequency variability over these areas. Here it is shown with a number of different diagnostics that the high predictive skill for the NAO/AO indeed translates to more accurate predictions of temperature, surface pressure, and precipitation in the areas of influence of this teleconnection.

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Not a surprise if you know this article: 

https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2017GL072832

Here evidence is presented that tropical upwelling changes related to the 11 year solar cycle also modulate the boreal winter MJO. Based on 37.3 years of MJO amplitude data, the largest amplitudes and occurrence rates, and the weakest static stabilities in the tropical lower stratosphere, occur during the QBOE phase under solar minimum (SMIN) conditions while the smallest amplitudes and strongest static stabilities occur during the QBOW phase under solar maximum (SMAX) conditions. Conversely, when the QBO and solar forcings are opposed (QBOW/SMIN and QBOE/SMAX), the difference in occurrence rates becomes statistically insignificant.

 

With some comments over here:

https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2017JD028171

Activities of the Madden‐Julian Oscillation (MJO) in boreal winter has recently been found to be stronger in easterly phases of the stratospheric quasi‐biennial oscillation (QBO) than its westerly phases. This QBOMJO connection was investigated in this study using a method that identifies individual MJO events by tracking their eastward propagating signals in precipitation. Stronger MJO activities in QBO easterly phases are a consequence of more MJO days, not larger amplitudes of individual MJO events as previously thought. More MJO days come from more MJO events initiated over the Indian Ocean and their longer duration because of a weaker barrier effect of the Maritime Continent on MJO propagation. Zonal heterogeneity exists in the connection between QBO, MJO, and tropical total precipitation in general. This poses a challenge to our current understanding of the MJO dynamics, which has yet to fully include upper‐tropospheric and stratospheric processes.

 

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Just published with open access (according to one of the authors)

The influence of the stratospheric state on North Atlantic weather regimes

Quote

Stratosphere–troposphere coupling is often viewed from the perspective of the annular modes and their dynamics. Despite the obvious benefits of this approach, recent work has emphasised the greater tropospheric sensitivity to stratospheric variability in the Atlantic basin than in the Pacific basin. In this study, a new approach to understanding stratosphere–troposphere coupling is proposed, with a focus on the influence of the stratospheric state on North Atlantic weather regimes (during extended winter, November to March). The influence of the strength of the lower‐stratospheric vortex on four commonly used tropospheric weather regimes is quantified. The negative phase of the North Atlantic Oscillation is most sensitive to the stratospheric state, occurring on 33% of days following weak vortex conditions but on only 5% of days following strong vortex conditions. An opposite and slightly weaker sensitivity is found for the positive phase of the North Atlantic Oscillation and the Atlantic Ridge regime. For the North Atlantic Oscillation regimes, stratospheric conditions change both the probability of remaining in each regime and the probability of transitioning to that regime from others. A logistic regression model is developed to further quantify the sensitivity of tropospheric weather regimes to the lower stratospheric state. The logistic regression model predicts an increase of 40–60% in the probability of transition to the negative phase of the North Atlantic Oscillation for a one standard deviation reduction in the strength of the stratospheric vortex. Similarly it predicts a 10–30% increase in the probability of transition to the positive phase of the North Atlantic Oscillation for a one standard deviation increase in the strength of the stratospheric vortex. The stratosphere–troposphere coupling in the European Centre for Medium‐range Weather Forecasts Integrated Forecasting System model is found to be consistent with the re‐analysis data by fitting the same logistic regression model.

https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/qj.3280

Edited by knocker
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The vortex strength at this time of the year is not particular indicative as to how it might progress. The chart below shows the correlation between the 10mb zonal wind and its strength at intervals between 7-42 days later. At this time of year (end of September / start of October) the predictability is at its lowest, only correlating a week in advance. At the end of October / start of November the zonal wind is fairly predictable a month and a half ahead as the vortex is properly formed at this point and is generally too early for major warmings in this period. After this, long term correlations fall as warmings affect the dataset, but short term the vortex increases in predictability for one and two weeks in advance and is fairly stable up to three weeks - the kind of timescales that warmings may take to materialise.

1988832854_u1060cor.thumb.png.f898fb6ecdcd84aa7600b8b8ded6c074.png

 

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https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018GL078838 

If the winter NAO is strongly negative or positive the models show this in advance. 

Recent studies of individual seasonal forecast systems have shown that the wintertime North Atlantic Oscillation (NAO) can be skillfully forecast. However, it has also been suggested that these skillful forecasts tend to be underconfident, meaning that there is too high a proportion of unpredictable noise in the forecasts. We assess the skill and overconfidence/underconfidence of the seasonal forecast systems contributing to the EUROpean Seasonal to Interannual Prediction (EUROSIP) multimodel ensemble system. Five of the seven systems studied have significant skill for forecasting the wintertime NAO at 2‐ to 4‐month lead times. Four of these skillful systems are underconfident for forecasting the NAO. A multimodel ensemble (ensemble size 126 members) is both skillful and clearly underconfident. Underconfidence becomes more pronounced as the ensemble size increases. Certain years in the hindcast period are well forecast by all or most models. This implies that common teleconnections and drivers of the NAO are being captured by the EUROSIP seasonal forecasts.

Plain Language Summary

In this paper we provide an intercomparison of seven seasonal forecast systems, with particular focus on the wintertime North Atlantic Oscillation (NAO). The wintertime NAO is the main driver of winter weather variability in the United Kingdom and Europe, and being able to forecast the NAO for the season ahead has potential benefits for many different sectors such as agriculture, energy, health, transport, and water resource management. We show that five of the seven systems studied can skillfully forecast the NAO, and a multimodel ensemble has even higher skill. Four of these skillful systems are found to be underconfident, which means that there is too high a proportion of unpredictable noise in the model. Being underconfident makes it more difficult to fully utilize the skill of a forecast. However, one system is skillful but not underconfident. We also find that there are common years in which the NAO is well forecast by all the skillful systems. This is an important result because it implies that common drivers of NAO predictability are being captured by these systems. These results are an important contribution to our understanding of seasonal forecasts systems and the predictability of the NAO.

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