Missed this yesterday but the 12Z EC was noteworthy for showing a split of the vortex up to 30hPa and certainly a stretched vortex even up at 10hPa. 00Z run, however, less keen, but still signs that the vortex will come under duress looking ahead...
http://twitter.com/MattHugo81/status/11 ... 6649527297
Stratosfeer winter 2019/2020
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Sebastiaan
- Berichten: 12294
- Lid geworden op: 31-12-1977
Re: Stratosfeer winter 2019/2020
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Re: Stratosfeer winter 2019/2020
De troposfeer sontwikkelt zich zeer gunstig voor een verstoring van de stratosferische vortex.
Veel wave1 op langere termijn
Ook binnen de tiendaagse is er al iets zichtbaar
De verstoring leidt niet meteen tot een SSW, maar kan wel de aanzet tot iets groters zijn. Dat zien we wel vaker, eerst een displacement en bij nieuwe wave (liefst wave2) ook een split.
Het lijkt me, kijkende naar de stratosferische zonale wind, dat de QBO snel negatief zal zijn, in ieder geval al in januari.
De verstoring leidt niet meteen tot een SSW, maar kan wel de aanzet tot iets groters zijn. Dat zien we wel vaker, eerst een displacement en bij nieuwe wave (liefst wave2) ook een split.
Het lijkt me, kijkende naar de stratosferische zonale wind, dat de QBO snel negatief zal zijn, in ieder geval al in januari.
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Re: Stratosfeer winter 2019/2020
Nog even de zuidelijke SSW (minor). Die heeft stevig doorgezet en de zonale wind is nu negatief.
De doorwerking in de troposfeer is ook evident. Van hetzelfde kaliber als in 2002. Vertaalt zich ook in de SOI: Met uitzicht op een El Nino 3.4 (30% kans)
Ik zie mogelijk ook verband met de extreme droogte in New South Wales.
De doorwerking in de troposfeer is ook evident. Van hetzelfde kaliber als in 2002. Vertaalt zich ook in de SOI: Met uitzicht op een El Nino 3.4 (30% kans)
Ik zie mogelijk ook verband met de extreme droogte in New South Wales.
Je hebt niet voldoende permissies om de bijlagen van dit bericht te bekijken.
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Sebastiaan
- Berichten: 12294
- Lid geworden op: 31-12-1977
-
Sebastiaan
- Berichten: 12294
- Lid geworden op: 31-12-1977
Re: Stratosfeer winter 2019/2020
Presentatie Ventrice over februari 2018 SSW
https://ams.confex.com/ams/2019Annual/v ... ngid=50319
https://ams.confex.com/ams/2019Annual/v ... ngid=50319
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Sebastiaan
- Berichten: 12294
- Lid geworden op: 31-12-1977
Re: Stratosfeer winter 2019/2020
That famous stratospheric teleconnection where SSW event means westerlies... Very interesting runs of the GloSea Model at the moment.
http://twitter.com/Met_Set_UK?ref_src=t ... 0%3Fs%3D20
http://twitter.com/Met_Set_UK?ref_src=t ... 0%3Fs%3D20
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Sebastiaan
- Berichten: 12294
- Lid geworden op: 31-12-1977
Re: Stratosfeer winter 2019/2020
Zonale snelheid dondert naar beneden.
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Re: Stratosfeer winter 2019/2020
Textbook Judah Cohen
https://www.esrl.noaa.gov/psd/events/20 ... -cohen.pdf
https://www.esrl.noaa.gov/psd/events/20 ... -cohen.pdf
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Sebastiaan
- Berichten: 12294
- Lid geworden op: 31-12-1977
Re: Stratosfeer winter 2019/2020
Update Cohen
Summary
The Arctic Oscillation (AO) is currently negative and is predicted to remain negative for the next two weeks.
The current negative AO is reflective of mostly positive pressure/geopotential height anomalies across the Arctic and mixed pressure/geopotential height anomalies across the mid-latitudes. The North Atlantic Oscillation (NAO) is near neutral with mixed pressure/geopotential height anomalies spread across Greenland and Iceland; and the NAO is predicted to remain near neutral as geopotential height anomalies remain weak across Greenland.
This week, troughing/negative pressure/geopotential height anomalies over Western Europe are predicted to be sandwiched by ridging/positive geopotential height anomalies in the central North Atlantic and Western Asia. Normal to below normal temperatures are predicted for Western Europe including the United Kingdom (UK) under northerly flow while normal to above normal temperatures are predicted for Eastern Europe under southerly flow. However, over the next two weeks the ridging in Western Asia will push north into the Barents-Kara Seas allowing cold air in Siberia to flow west underneath the ridge into Northern Europe.
Currently temperatures are mostly above normal across Western Asia and Southeastern Asia as ridging/positive geopotential height anomalies dominate Western and Southern Asia while temperatures are below normal in Siberia with troughing/negative pressure/geopotential height anomalies dominating the region. However, over the next two weeks, ridging/positive geopotential height anomalies currently centered over the Caspian Sea eventually will drift north into the Barents-Kara Seas allowing troughing/negative geopotential height anomalies with below normal temperatures to stretch across Northern Asia and Northern Europe.
This week ridging/positive geopotential height anomalies are predicted to dominate western North America with normal to above normal temperatures for Alaska and the West Coasts of Canada and the United States and troughing/negative geopotential height anomalies over eastern North America with normal to below normal temperatures east of the Rockies both in Canada and the US. However, over the next two weeks the pattern is predicted to flip with troughing in western North America with cooler temperatures and ridging in eastern North America temperatures turning milder.
In the Impacts section I discuss how the atmosphere is predicted to respond to above normal October Eurasian snow cover extent consistent with previous research.
Impacts
Last week I included the graphic of the six-step process of how snow cover advance in October can influence the behavior of the stratospheric polar vortex (PV) in early winter and mid-to late winter weather. This year Eurasian snow cover extent was above normal and therefore I would expect a relatively perturbed or disrupted PV most likely in January followed by a prolonged period where the AO is on average negative and cold temperatures across the mid-latitudes from late January into February. But before then there are two other steps. And of course as we saw last winter an even highly perturbed PV does not guarantee to be followed by a meaningful period of a negative AO.
The first step following above normal Siberian October snow cover are cold temperatures in Siberia. This is coupled with a northwestward expansion of the Siberian high and ridging/blocking in the mid-troposphere in the Urals/Scandinavian region. I just did a quick correlation of October Siberian with November surface temperatures shown in Figure i. Above normal October Siberian snow cover extent is followed by below normal temperatures in Siberia that extend southwestward towards the Persian Gulf and warm temperatures in the Middle East and Eastern Europe. Temperatures are also above normal in western North America, in particular Alaska. Also included in Figure i, is the latest CFS surface temperature forecast for November and the similarity to the temperature response to above normal snow cover is striking. Predicted are below normal temperatures in Siberia that extend southwestward towards the Persian Gulf, relatively warm temperatures in the Middle East and Eastern Europe and warm temperatures in western North America including Alaska.
Figure i. a) Correlations October Eurasian snow cover extent with Northern Hemsiphre surface temperatures1949 through 2004. b) Forecasted average surface temperature anomalies (°C; shading) across the Northern Hemisphere for November 2019. The forecasts are from the 11 November 2019 CFS. -> PLAATJES UPLOADEN LUKT NIET, WEBP BESTAND
As I discussed last week, the response to above normal October Siberian snow cover in pressure/heights is a northwestward expansion of the Siberian high. Last week I showed the analysis for the mid-troposphere but in Figure ii, I show the analysis for sea level pressure (a plot that I have shown many times previously in the blog from Cohen et al. 2014). The northwestward expansion of the Siberian high is coupled with relatively low pressure in the respective ocean basins, forming a tripole pattern. This pattern is also favorable for exciting vertical energy transfer from the troposphere into the stratosphere. Also included in Figure ii is the predicted November SLP from this morning’s CFS. Again, the SLP pattern predicted for November is strikingly similar to the pattern shown to be the response to above normal October snow cover. Also included in Figure ii is the average SLP pattern 0-45 days prior to a PV displacement and it is characterized by the northwestward expansion of the Siberian High coupled with deep low pressure in the northern North Pacific as shown in Cohen and Jones 2011. Again, there is a strong similarity between the predicted November average SLP pattern and the pattern most favorable for initiating a PV displacement. Therefore, in my opinion the atmospheric response to above normal October Siberian snow cover has been “textbook,” which is also highly favorable to initiating vertical energy transfer from the troposphere to the stratosphere that disrupts the PV. And given the spatial scale of the blocking high pressure across northern Eurasia, it projects more onto wave one that favors a PV displacement over a PV split.
Figure ii. a) Regression of November SLP anomalies (hPa) onto October monthly mean, October Eurasian SCE (contouring) and December meridional heat flux anomalies at 100 hPa, averaged between 40-80°N (shading). b) Predicted average sea level pressure (hPa; contours) and sea level pressure anomalies (hPa; shading) across the Northern Hemisphere from November 11, 2019 through November 30, 2019. The forecasts are from the 11 November 2019 CFS. c) Sea level pressure anomaies (hPa) averaged 45 to zero days prior to polar vortex displacements. -> PLAATJES UPLOADEN LUKT NIET, WEBP BESTAND
From Figure 12 below the vertical energy transfer is responding to the atmospheric circulation and is predicted to become more active in the next couple of weeks, which I expect will continue well into December. I do believe that a significant PV disruption is becoming more and more likely but is not guaranteed. As I have discussed over the past year there is vertical energy transfer that can result in a “reflective” PV disruption and alternatively vertical energy transfer that can result in an absorptive PV disruption. A reflective event is characterized by positive vertical energy transfer anomalies or vertical wave activity Flux (WAFz) quickly followed by negative WAFz anomalies. The PV itself is stretched but often not displaced. Also, the cold temperature response to a reflective event are focused in North America east of the Rockies. If you look at Figure 12 below you can see a reflective event at the end of October and early November identified by a red blue striation or positive anomalies quickly followed by negative anomalies. I do believe this reflective event is at least partially responsible for the cold air outbreaks of last week and this week.
In contrast during absorptive events the WAFZ is consistently positive until the climax of the PV disruption. Also, the cold temperature response to an absorptive event are focused in Eurasia. Also, I have discussed many times that during positive WAFz leading to an absorptive PV disruption, temperatures tend to be mild in eastern North America but cold in East Asia. Again, in Figure 12 the predicted WAFz anomalies are predicted to be positive only over the next two weeks. Also, the PV is predicted to be displaced towards Eurasia (see below Figure 13). This is looking to me like we are transitioning from a reflective PV disruption in early November to potentially an absorptive PV disruption in late November. The biggest immediate impact on Northern Hemisphere (NH) temperatures would be a shift of cold temperatures from North America to Eurasia. The positive WAFz leading up to an absorptive PV disruption can last up to six weeks. So potentially we are at the beginning of a multi week period of overall mild temperatures in eastern North America.
When I tweeted on Friday about the potential for more cold air for eastern North America based on a minor PV disruption, I had assumed another reflective event. Much of this was based on the time of year. It seems to me that positive WAFz in November most often is associated with reflective events and only later in December and January are the positive WAFz anomalies associated with absorptive events. This was the case the last two years. These events are much easier to diagnose in hindsight, so I am not committing to one type of event or another. As of today, it is starting to look like more of an absorptive event to me but I don’t rule out a reflective event just yet. If it is a reflective event, then I do believe it can turn colder in eastern North America. And even if it is an absorptive event, short-lived cold outbreaks are still possible.
Longer term if it is the beginning of absorptive positive WAFz, this could be the initiation of a significant PV disruption. But this takes time and I would guess the earliest would be the second half of December. So far, our speculative polar vortex model does not indicate a significant PV disruption through December 11, but I think over time it will show greater confidence in one based on the predicted NH atmospheric circulation. http://www.aer.com/science-research/cli ... cillation/
Summary
The Arctic Oscillation (AO) is currently negative and is predicted to remain negative for the next two weeks.
The current negative AO is reflective of mostly positive pressure/geopotential height anomalies across the Arctic and mixed pressure/geopotential height anomalies across the mid-latitudes. The North Atlantic Oscillation (NAO) is near neutral with mixed pressure/geopotential height anomalies spread across Greenland and Iceland; and the NAO is predicted to remain near neutral as geopotential height anomalies remain weak across Greenland.
This week, troughing/negative pressure/geopotential height anomalies over Western Europe are predicted to be sandwiched by ridging/positive geopotential height anomalies in the central North Atlantic and Western Asia. Normal to below normal temperatures are predicted for Western Europe including the United Kingdom (UK) under northerly flow while normal to above normal temperatures are predicted for Eastern Europe under southerly flow. However, over the next two weeks the ridging in Western Asia will push north into the Barents-Kara Seas allowing cold air in Siberia to flow west underneath the ridge into Northern Europe.
Currently temperatures are mostly above normal across Western Asia and Southeastern Asia as ridging/positive geopotential height anomalies dominate Western and Southern Asia while temperatures are below normal in Siberia with troughing/negative pressure/geopotential height anomalies dominating the region. However, over the next two weeks, ridging/positive geopotential height anomalies currently centered over the Caspian Sea eventually will drift north into the Barents-Kara Seas allowing troughing/negative geopotential height anomalies with below normal temperatures to stretch across Northern Asia and Northern Europe.
This week ridging/positive geopotential height anomalies are predicted to dominate western North America with normal to above normal temperatures for Alaska and the West Coasts of Canada and the United States and troughing/negative geopotential height anomalies over eastern North America with normal to below normal temperatures east of the Rockies both in Canada and the US. However, over the next two weeks the pattern is predicted to flip with troughing in western North America with cooler temperatures and ridging in eastern North America temperatures turning milder.
In the Impacts section I discuss how the atmosphere is predicted to respond to above normal October Eurasian snow cover extent consistent with previous research.
Impacts
Last week I included the graphic of the six-step process of how snow cover advance in October can influence the behavior of the stratospheric polar vortex (PV) in early winter and mid-to late winter weather. This year Eurasian snow cover extent was above normal and therefore I would expect a relatively perturbed or disrupted PV most likely in January followed by a prolonged period where the AO is on average negative and cold temperatures across the mid-latitudes from late January into February. But before then there are two other steps. And of course as we saw last winter an even highly perturbed PV does not guarantee to be followed by a meaningful period of a negative AO.
The first step following above normal Siberian October snow cover are cold temperatures in Siberia. This is coupled with a northwestward expansion of the Siberian high and ridging/blocking in the mid-troposphere in the Urals/Scandinavian region. I just did a quick correlation of October Siberian with November surface temperatures shown in Figure i. Above normal October Siberian snow cover extent is followed by below normal temperatures in Siberia that extend southwestward towards the Persian Gulf and warm temperatures in the Middle East and Eastern Europe. Temperatures are also above normal in western North America, in particular Alaska. Also included in Figure i, is the latest CFS surface temperature forecast for November and the similarity to the temperature response to above normal snow cover is striking. Predicted are below normal temperatures in Siberia that extend southwestward towards the Persian Gulf, relatively warm temperatures in the Middle East and Eastern Europe and warm temperatures in western North America including Alaska.
Figure i. a) Correlations October Eurasian snow cover extent with Northern Hemsiphre surface temperatures1949 through 2004. b) Forecasted average surface temperature anomalies (°C; shading) across the Northern Hemisphere for November 2019. The forecasts are from the 11 November 2019 CFS. -> PLAATJES UPLOADEN LUKT NIET, WEBP BESTAND
As I discussed last week, the response to above normal October Siberian snow cover in pressure/heights is a northwestward expansion of the Siberian high. Last week I showed the analysis for the mid-troposphere but in Figure ii, I show the analysis for sea level pressure (a plot that I have shown many times previously in the blog from Cohen et al. 2014). The northwestward expansion of the Siberian high is coupled with relatively low pressure in the respective ocean basins, forming a tripole pattern. This pattern is also favorable for exciting vertical energy transfer from the troposphere into the stratosphere. Also included in Figure ii is the predicted November SLP from this morning’s CFS. Again, the SLP pattern predicted for November is strikingly similar to the pattern shown to be the response to above normal October snow cover. Also included in Figure ii is the average SLP pattern 0-45 days prior to a PV displacement and it is characterized by the northwestward expansion of the Siberian High coupled with deep low pressure in the northern North Pacific as shown in Cohen and Jones 2011. Again, there is a strong similarity between the predicted November average SLP pattern and the pattern most favorable for initiating a PV displacement. Therefore, in my opinion the atmospheric response to above normal October Siberian snow cover has been “textbook,” which is also highly favorable to initiating vertical energy transfer from the troposphere to the stratosphere that disrupts the PV. And given the spatial scale of the blocking high pressure across northern Eurasia, it projects more onto wave one that favors a PV displacement over a PV split.
Figure ii. a) Regression of November SLP anomalies (hPa) onto October monthly mean, October Eurasian SCE (contouring) and December meridional heat flux anomalies at 100 hPa, averaged between 40-80°N (shading). b) Predicted average sea level pressure (hPa; contours) and sea level pressure anomalies (hPa; shading) across the Northern Hemisphere from November 11, 2019 through November 30, 2019. The forecasts are from the 11 November 2019 CFS. c) Sea level pressure anomaies (hPa) averaged 45 to zero days prior to polar vortex displacements. -> PLAATJES UPLOADEN LUKT NIET, WEBP BESTAND
From Figure 12 below the vertical energy transfer is responding to the atmospheric circulation and is predicted to become more active in the next couple of weeks, which I expect will continue well into December. I do believe that a significant PV disruption is becoming more and more likely but is not guaranteed. As I have discussed over the past year there is vertical energy transfer that can result in a “reflective” PV disruption and alternatively vertical energy transfer that can result in an absorptive PV disruption. A reflective event is characterized by positive vertical energy transfer anomalies or vertical wave activity Flux (WAFz) quickly followed by negative WAFz anomalies. The PV itself is stretched but often not displaced. Also, the cold temperature response to a reflective event are focused in North America east of the Rockies. If you look at Figure 12 below you can see a reflective event at the end of October and early November identified by a red blue striation or positive anomalies quickly followed by negative anomalies. I do believe this reflective event is at least partially responsible for the cold air outbreaks of last week and this week.
In contrast during absorptive events the WAFZ is consistently positive until the climax of the PV disruption. Also, the cold temperature response to an absorptive event are focused in Eurasia. Also, I have discussed many times that during positive WAFz leading to an absorptive PV disruption, temperatures tend to be mild in eastern North America but cold in East Asia. Again, in Figure 12 the predicted WAFz anomalies are predicted to be positive only over the next two weeks. Also, the PV is predicted to be displaced towards Eurasia (see below Figure 13). This is looking to me like we are transitioning from a reflective PV disruption in early November to potentially an absorptive PV disruption in late November. The biggest immediate impact on Northern Hemisphere (NH) temperatures would be a shift of cold temperatures from North America to Eurasia. The positive WAFz leading up to an absorptive PV disruption can last up to six weeks. So potentially we are at the beginning of a multi week period of overall mild temperatures in eastern North America.
When I tweeted on Friday about the potential for more cold air for eastern North America based on a minor PV disruption, I had assumed another reflective event. Much of this was based on the time of year. It seems to me that positive WAFz in November most often is associated with reflective events and only later in December and January are the positive WAFz anomalies associated with absorptive events. This was the case the last two years. These events are much easier to diagnose in hindsight, so I am not committing to one type of event or another. As of today, it is starting to look like more of an absorptive event to me but I don’t rule out a reflective event just yet. If it is a reflective event, then I do believe it can turn colder in eastern North America. And even if it is an absorptive event, short-lived cold outbreaks are still possible.
Longer term if it is the beginning of absorptive positive WAFz, this could be the initiation of a significant PV disruption. But this takes time and I would guess the earliest would be the second half of December. So far, our speculative polar vortex model does not indicate a significant PV disruption through December 11, but I think over time it will show greater confidence in one based on the predicted NH atmospheric circulation. http://www.aer.com/science-research/cli ... cillation/
Re: Stratosfeer winter 2019/2020
Even de plaatjes erbij: Het hoog boven West-Rusland (in deze tijd van het jaar) is helemaal niet zo ongunstig voor winterweer als veelal wordt gedacht. Op de lange termijn krijg je het, als het goed is, terugbetaald in de vorm van een stratosferische opwarming.Sebastiaan schreef: ↑12-11-2019 11:06Update Cohen
Longer term if it is the beginning of absorptive positive WAFz, this could be the initiation of a significant PV disruption. But this takes time and I would guess the earliest would be the second half of December. So far, our speculative polar vortex model does not indicate a significant PV disruption through December 11, but I think over time it will show greater confidence in one based on the predicted NH atmospheric circulation. http://www.aer.com/science-research/cli ... cillation/
Wel een complex dingetje, die adsorptive positive WAFz, eens kijken of we in de aanstaande winterbespreking een vraag over kunnen stellen.
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