Stratosfeer winter 2019/2020

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Ronald
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Lid geworden op: 01-01-2009

Re: Stratosfeer winter 2019/2020

Bericht door Ronald » 21-11-2019 21:58

Bedankt Paul, bijdrage van een helder en hoog niveau, letterlijk en figuurlijk :D

Sebastiaan
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Re: Stratosfeer winter 2019/2020

Bericht door Sebastiaan » 22-11-2019 19:40

Stratofreaks
Hier kunnen jullie de presentaties zien van de EC-bijeenkomst over de stratosfeer -> http://events.ecmwf.int/event/129/timetable/

Karel
Berichten: 2366
Lid geworden op: 01-08-1978

Re: Stratosfeer winter 2019/2020

Bericht door Karel » 23-11-2019 10:04

Bedankt Sebastiaan. De bijdrage van Marlene Kretschmer over de analyse van de periode 1979-2017 en de analyse van 2018 zijn wel zeer illustratief voor de mogelijke effecten van Stratosferische opwarming op de troposfeer. Vergelijk Cluster 4 en Cluster 5. Amerika versus Eurasia!

Sebastiaan
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Re: Stratosfeer winter 2019/2020

Bericht door Sebastiaan » 23-11-2019 10:30

http://events.ecmwf.int/event/129/contr ... meisen.pdf
2/3 heeft negatieve NAO, de rest dus niet.
Synoptische setting op moment van SSW speelt volgens haar een rol of er trop. impact is.
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Ronald
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Is deze mogelijke ontwikkeling nou een gevolg?

Bericht door Ronald » 24-11-2019 10:17

De waarschijnlijke opwarming in de stratosfeer zit nog steeds in de modellen.
Geplaatste kaarten laten de start over een dag of 5 zien en de situatie op dag 10.

In de troposfeer zien we de laatste 2 runs, na 3 a 4 dramatische runs voor 1e deel december, signalen voor hernieuwde drukstijgingen ten oosten en noordoosten, waardoor die enige malen geschetste krachtige westcirculatie er toch niet lijkt te komen die periode.

Zijn deze -virtuele- drukstijgingen nou te herleiden tot die stratosferische opwarming?
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Sebastiaan
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Re: Stratosfeer winter 2019/2020

Bericht door Sebastiaan » 25-11-2019 15:16

Allereerst EC 10 hPa -> zo'n lage m/s zag ik nog niet eerder.
Daarnaast EC 150 hPa. Je zou toch zeggen dat er vanuit 'boven' steun is voor Blokkade op de oceaan. Ik geloof dan ook niet in een doordreunende WC.
Je hebt niet voldoende permissies om de bijlagen van dit bericht te bekijken.

Sebastiaan
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Lid geworden op: 01-01-1978

Re: Stratosfeer winter 2019/2020

Bericht door Sebastiaan » 26-11-2019 10:37

Update Cohen.

Still I am treating the upcoming PV disruption mostly as an absorptive event. This could be the most important weather event of the upcoming winter for the NH. As the energy transfer increases from the troposphere to the stratosphere, I expect an overall milder pattern across the NH with two possible regional exceptions – East Asia and western North America. It does seem to me that this scenario is consistent with the model forecasts heading into mid-December. Close to the peak of the PV disruption I would expect some immediate and short-lived tropospheric response with some regional severe winter weather. Then about two weeks later I would expect a more long-lasting and larger scale increase in severe winter weather across the NH but there will be places that will turn milder and it is difficult to know ahead of time. Based on past events the most likely place to see colder temperatures is Siberia (I know what you are thinking - who cares, its cold no matter what). But I do think that warm sea surface temperatures in the Gulf of Alaska favor downstream troughing and cold and possibly snowy weather across the interior of North America.

If the PV disruption is significant and the coupling with the troposphere robust, this could potentially setup a cold January possibly persisting into February across large regions of the NH. On the other hand, if the PV disruption and/or the coupling with the troposphere are weaker than anticipated then we could be off to the races as far as NH temperatuers.

Ironically, I was thinking, though I argue that PV disruptions lead to more severe winter weather across the NH mid-latitudes, the only guarantee with PV disruption seems to be a multi week period of milder weather for Europe and the Eastern US leading up to and including the PV disruption. Much more ephemeral is a multi-week and even multi-month period of severe winter weather for those regions. It is almost damned if you do and damned if you don’t. If the PV is stable and strong that overwhelmingly favors mild weather and if the PV is significantly disrupted only milder weather is nearly for certain with much more uncertainty with the ensuing severe winter weather. The one possible exception seems to me are the reflected PV events where there seems to be a much stronger likelihood of North American cold weather east of the Rockies.

Sebastiaan
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Lid geworden op: 01-01-1978

Re: Stratosfeer winter 2019/2020

Bericht door Sebastiaan » 27-11-2019 11:55

Op de LT zien we lagedruk bij de Aleoeten, dat is gunstig voor verdere druk op de strat. Poolwervel. Een ander deel van de trop. poolwervel belandt boven Scandinavië.

Sebastiaan
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Lid geworden op: 01-01-1978

Re: Stratosfeer winter 2019/2020

Bericht door Sebastiaan » 27-11-2019 15:58

Zie net een update van Stewart. Hij refereert ook naar het laag bij de Aleoeten.

Looks to me as if the early winter skirmishes are confirming two things:

-stratospheric polar vortex weaker than normal;
-stratospheric polar vortex displaced towards the Siberian Sector.

That should temper enthusiasm for proper early season cold across Europe as it doesn't favour sufficient blocking strength to displace cold air masses south and westwards to the degree necessary.

Tropospherically, our low frequency base state, which is nicely evident across OLR anomaly fields in the Tropics....

... is about to undergo destructive interference in the next two weeks as a more coherent convective wave develops and pushes further east. This is a good signal for the PV to rev up a bit and westerly influence extend across the North Atlantic.

When this relaxes, the low frequency state should take hold again on the hemispheric pattern. Deep upper low in the North / North-east Pacific a facet of this which should to further reinforcement of the weaker and displaced (Wave 1) SPV.

Weak level blocking expected to re-establish to our north and north-east within a broadly north-west flow regime for second half of December. It will be interesting to see how much angular momentum rebounds in the next 2 weeks after being driven to lowish values of late, as this will be key to how much amplification in the upper level flow across the Pacific and Atlantic can be generated to tease out Arctic air masses within that regime.

Sebastiaan
Berichten: 5458
Lid geworden op: 01-01-1978

Re: Stratosfeer winter 2019/2020

Bericht door Sebastiaan » 27-11-2019 16:00

https://www.netweather.tv/forum/topic/6 ... nt=4103736
UKMO houdt e.e.a. in de gate maar ziet nog geen signalen die wijzen op koud weer.

Monday 9 December – Monday 23 December

Staying unsettled with temperatures near normal

The broadly unsettled theme is expected to continue during the middle couple of weeks of December. Low pressure systems are expected to move in from the north Atlantic, passing close to or across the UK as they head towards Scandinavia. During November, the predominant low pressure track has been over southern England or even down over France and Spain. This has prevented the UK from being influenced by the mild south-westerly winds that often accompany our wet weather in winter, so it has been chilly and also wet! The mid-December pattern should be more typical of a UK winter, so whilst it looks like we will see bouts of wet and possibly windy weather, temperatures should be nearer normal for the time of year.

The week of the General Election looks likely to be unsettled with spells of rain and blustery winds sweeping across the UK. Any colder interludes between the frontal rain bands should be brief, so the main weather hazards should be related to the wind and rainfall rather than snow and ice. Looking beyond mid-month and most indications suggest that the unsettled weather will continue. However, we are still monitoring the Arctic stratosphere, as there is a chance that developments here could lead to a spell of colder weather in December. At the moment, whilst there is some uncertainty in the forecast, we don't see any long, drawn out spells of wintry weather developing.

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