Stratosphere and Polar Vortex Watch 2020

[sebastiaan1973]

Conclusions from the article.

4. Conclusions

The intraseasonal variability in tropical heating related to the MJO can exert an impact on the stratospheric polar vortex (e.g. Garfinkel et al 2012, 2014). However, there has been little written about the propagation features and intensity of the MJO after SSW event occur. In the present study, it is expected that SSWs can affect the MJO based on the above findings. The dominant occurrence of MJO phases 6 and 7; the simultaneously enhanced convective activity over the equatorial Central and Western Pacific during 1 ~ 24 d after onset of SSW events; and then the coherent eastward propagation of tropical intraseasonal convection in the following days all indicate that the influence of SSWs on tropical intraseasonal convection related to the MJO cannot be ignored. Although the dynamic and physical mechanism(s) are unclear, this SSW–MJO link is consistent with the thermal stratification change in the tropical upper troposphere.

Presumably, the SSW–MJO link is associated with multiple factors. The responses of static stability in the tropical upper troposphere and lower stratosphere (UTLS) to SSW event described above may not be the sole potential mechanism by which SSW affects the MJO. Other mechanisms, such as vertical wind shear (Ho et al 2009), absolute vorticity (Collimore et al 2003), and tropopause changes (Gray et al 1992), can also be adopted to explain the responses of tropical convection to the anomaly in the UTLS region. Thus, to identify the exact mechanism(s), further studies using both observations and numerical model simulations are necessary.

The impacts from SSWs could affect tropical intraseasonal convection related to MJO on time scales exceeding 20 d. More importantly, this work demonstrated the complex relationship between the MJO and SSW. Previous studies have shown a strong impact of the MJO on the NH wintertime stratospheric polar vortex. However, the results of this study allude to the reverse route, i.e. alteration of the tropical intraseasonal convection related to the MJO due to the abrupt change in the extratropical stratosphere. Although the results need to be further confirmed by numerical models that resolve stratospheric processes, this study suggests that SSW is indispensable for the subseasonal-to-seasonal prediction of the evolution of MJO. In this regard, it is also anticipated that the statistical prediction of MJO could be improved by taking variability in the extratropical stratosphere into consideration as a potential predictor especially in boreal winter.

-> So, there seems to be a delay in MJO reponse.

[bluearmy]

Signs on the 00z ec op of a split beyond day 10 

 

[Vikos]

A look in the stratosphere, there are still big question marks regarding the coupling between the vortex in the stratosphere (SPV) and the Troposphere (TPV). Repeatedly expected heat flows from the Asian Sector still do not allow a thorough regeneration of the vortex. At the beginning of the medium term range, in 10 hPa around the Laptev and Kara seas however, the medium term should shift rapidly towards Greenland, while an extensive anti-cyclone across the North Pacific sector did this forced "displacement" of the SPW.

Similar, there is also the downtransition area SPV to TPV wich can be made out, although the vortex currents there is quite weak. It is interesting that at least the GEFS indicates a coupling at the beginning of the medium term. So far so good. However, numerics models have massive problems with the pressure forecast throughout the arctic area. This is evident in the distinctive run-to-run Discrepancies in the pressure minima of sometimes several hundred kilometers, as well repeated strongly changing cross-polar cold flows from the Asian sector initially in the Canadian, now increasingly in the Scandinavian / Siberian area (possibly consequences of the indicated coupling between SPV and TPV?). A look at the ensemble spread also shows Uncertainties quickly become so lasting that any detailed work becomes obsolete.

But what is noticeable in the troposphere is an increase in the wave number comparatively short amplitudes and thus increased progressivity. This wave train is forced by repeated positive ones anomaly maxima in the 500 hPa geopotential field around the Aleutian Islands. These wander swiftly over North America to the east, but on a southerly track. This is owed due an abnormally high geopotential over the Canadian Arctic Archipelago or, in other words, a retrograde to the west offset negative NAO anomaly, which is even increasingly starting to the west, that the calculated NAO gradually slips towards the 0-line.

The NAO / AO however, remain in the negative range, with the member scatter at the end of the Increases dramatically in the medium term, but this is due to the shift of the TPV in the direction of Greenland, this caues a development wich is close to North Pole for then falling geopotential. This southern Rossby wave train now interacts over the medium term with an air mass over the eastern tropical and subtropical Atlantic, which is extremely warm with a view to the model climate (e.g. caused due to largely positive anomalies of the water surface temperature, but also by remnants of an intense subtropical that predominated until recently Anticyclones over the Canaries, the strong desert air advehed to the west and further heated by subsidence). This air mass is between the vigorous Atlantic lows and an anticyclone over Morocco, and it is (slowly weakening) led to the northeast.

Although the air mass cools down a little when it is lifted, nevertheless, the medium term can exceed 850 hPa in south-west and south of Europe Temperature values of 10-15 degrees are expected. The EFI underlines that unusual warmth in southwestern Europe with values of 0.8-1 and an SOT of partly over +1. If you look at the corresponding CDFs, you can see very steep ones Gradients (signs of high security) in the record range. Also the EFI 2m values (weekly averaged) this medium-term is about between the Iberian Peninsula and North Africa between 0.8 and 1 and on the basis of selected meteograms we are beyond the 99th percentile. Or in other words: Record values are particularly possible in Spain and across North Africa.

The western edge of this warm air mass gets in track of the rain Atlantic Low pressure Activity that initiates a pronounced so-called "atmospheric flow", which leads with predicted integrated water vapor values of 30-40 mm much moisture in to Western and partly also to Central Europe. That means that from the west swiveling low pressure areas following an abnormally warm and humid Have air mass and thus abundant precipitation for parts of Western and Central Europe becomes an issue.

[Don]

45 minutes ago, Vikos said:

The western edge of this warm air mass gets in track of the rain Atlantic Low pressure Activity that initiates a pronounced so-called "atmospheric flow", which leads with predicted integrated water vapor values of 30-40 mm much moisture in to Western and partly also to Central Europe. That means that from the west swiveling low pressure areas following an abnormally warm and humid Have air mass and thus abundant precipitation for parts of Western and Central Europe becomes an issue.

Thanks Vikos for the detailed update.  Just a question, how do you see these current developments potentially impacting the UK moving forward as I don't have a great understanding of the subject, or is that too tricky to answer at this stage?

 

Edited January 25, 2021 by Don

[bluearmy]

Differences between ec and gfs by day 10 

ec again looks like splitting by end week 2 in the Svalbard area 

gfs looks like it wants to end up with Atlantic strat ridge into greeny again 

either way it’s a strat ridge to our north west or northeast into mid feb 

[mountain shadow]

3 hours ago, bluearmy said:

Differences between ec and gfs by day 10 

ec again looks like splitting by end week 2 in the Svalbard area 

gfs looks like it wants to end up with Atlantic strat ridge into greeny again 

either way it’s a strat ridge to our north west or northeast into mid feb 

Let's hope we get a proper 500mb level response in the trop.

[Griff]

3 minutes ago, Griff said:

Ecm zonal latest just in... More questions than answers perhaps? 

(I have a reminder to check) 

I've included the previous for comparison. 

ECM zonal latest... 

Edited January 25, 2021 by Griff

[damianslaw]

GFS 12z today shows a classic SSW after effect imprint, albeit 4-5 weeks after the event, so fairly late. Major scandi block and long drawn easterly.

[sebastiaan1973]

Impacts

I want to continue last week’s blog’s theme that the current PV disruption at least in my opinion is unusual and maybe unique in the observational record.  Long range prediction is challenging on the best of days and trying to anticipate the impacts of an unprecedented event or maybe as some like to say a “black swan” event (to be clear I am not suggesting there will be catastrophic consequences from the event just that it is rare and hard to have anticipated before it occurred) is many degrees more challenging.

There is consensus that in early January 2021 we observed a major mid-winter warming (MMW where the zonal winds reverse from westerly to easterly at 60°N and 10 hPa).  The event was a double dip affair with the winds briefly going westerly before going even more negative about a week later.  As I discussed last week, typically strong/active vertical Wave Activity Flux (WAFz and is proportional to poleward heat transport) should cease after a significant weakening of the PV, certainly an MMW.  As seen in Figure 12, there have been two more positive pulses one centered on mid-January and now an even bigger pulse to end the month of January.  It is not predicted by all models but at least by some models (and it seems to me most consistent by the ECMWF) have been predicting that this last pulse will result in yet another reversal of the winds from westerly to easterly at 60°N and 10 hPa. 

This is very unusual and has resulted in observing two separate phenomena typically not seen together, almost like seeing Superman and Clark Kent or Batman and Bruce Wayne in the same room at the same time as I will try to demonstrate.

This follows a tweet from last week.  I showed in last week’s blog a composite of the pressure-time plot of the North Annular Mode (NAM) from Polvani and Waugh (2004) but today I show the original composite of the pressure-time plot of the NAM (the same as the AO but I prefer the AO since in the troposphere the AO is not annular) from Baldwin and Dunkerton (2001) in Figure i.  This plot is comparable to the polar cap geopotential height anomalies (PCHs) shown in Figure 11 every week.  What the plot shows is that the negative NAM or AO propagates from the stratosphere to the surface with time and is often called the “dripping paint” plot for that very reason. 

Figure i. Composites of time-height development of the northern annular mode for (A) 18 weak vortex events. The events are determined by the dates on which the 10-hPa annular mode values cross –3.0. The indices are nondimensional; the contour interval for the color shading is 0.25, and 0.5 for the white contours. Values between 0.25 and 0.25 are unshaded. The thin horizontal lines indicate the approximate boundary between the troposphere and the stratosphere.  From Baldwin and Dunkerton (2001).

However, in Figure ii I show Figure 11 with arrows clearly delineating where the PCHs (proxy for the AO/NAM) both dripping down and up or as I tweeted doing loop-de-loops or twirls in the stratosphere like the Blue Angels.  Now at times it does appear as if the PCHs are propagating up but this is only during active WAFz prior to an MMW (and I include one at the end of December as an example) but not post an MMW.  Having simultaneous upward and downward PCHs seems very strange and unusual to me.  My explanation for the simultaneous upward and downward PCHs is we have the typically “dripping paint” phenomenon following an MMW simultaneous with active WAFz or vertical energy transfer as seen in Figure 12.  And as I discussed last week, I could not find another example of active WAFz post an MMW dating back to 1969.

Figure ii.  Observed and predicted daily polar cap height (i.e., area-averaged geopotential heights poleward of 60°N) standardized anomalies. The forecast is from the 00Z 25 January 2021 GFS ensemble. Blue arrows show downward propagaton of PCHs and yellow arrows show upward propagaton of PCHs.

As I have discussed in previous blogs, we observe Ural blocking ahead of a PV disruption (it is the trigger for the event) and Greenland blocking after the PV disruption.  I will admit that I don’t fully understand the physics behind this very sequence of events: Ural blocking-PV disruption-Greenland blocking but it appears in every analysis.  A cautionary tale of relying on empirical analysis without physical reasoning.  In Figure iii, I include my analysis from Cohen and Jones (2012) but you can see the same result in Mitchell et al. (2013).  Leading up the current PV disruption we observed strong Ural blocking (see for example the blog from 07 December 2020.  But now post the PV disruption we observe Greenland blocking but oddly enough the Ural blocking is still there (see Figure 3), it is like the dinner guest that overstayed its welcome or like having Superman and Clark Kent in the same room at the same time, it’s not supposed to happen.  As an aside it is a great question what has led to the persistence of the Ural blocking this winter season?  I have argued that below normal Barents Kara sea ice and above normal Siberian snow cover favor Ural blocking (see see http://rdcu.be/fJte but especially Box B2) both of which have been present in an impressive manner since the fall (see below Figure 16 and current observed snow depth).  But as much as I like to be provocative, even I won’t venture to make a linkage based on one data point especially when including last winter.  Excuse the bad pun but talk about polar opposites is comparing last winter when Ural blocking was nowhere to be found to this winter when Ural blocking just can’t quit.  So a good question without a good answer for now.

Figure iii.  Sea level pressure (SLP) anomalies (hPa) (a) averaged245 to 0 days prior to vortex displacements, (b)averaged 0 to 45 days after vortex displacements, (c) averaged 45 to 0 days prior to vortex splits, and (d) averaged 0 to 45 days after vortex splits. Colored shading represents anomalies, solid contours show the full values of the SLP field, and dashed contours represent 90% and 95% confidence levels. Mean values are computed daily over the reanalysis period 1948–2010. From Cohen and Jones (2012).

The PV split of January 2009 may just be the most impressive PV disruption that I can recall.  The PV was completely obliterated.  At the time, it set the record for strongest easterly winds ever observed at 60°N and 10 hPa and the winds remained easterly for a full month!  In Figure iv I present an animation of the PV disruption.  I want you to notice that once the warm air rushes the Arctic with the commencement of the MMW, it does not happen again. 

Figure iv. Observed 10 hPa geopotential heights (dam; contours) and temperature anomalies (°C; shading) across the Northern Hemisphere for 1 January - 28 February 2009. This is an older animation so please excuse the diiferent shading.

The central date or the day the winds first turned easterly/negative at 60°N and 10 hPa is January 24, 2009.  In Figure v, I include the WAFz from the entire winter of 2008/09.  This incredibly intense and long-lasting PV disruption was triggered by one WAFz pulse at the end of January.  Once the MMW commences, the spigot is shut off. 

Figure v. Observed daily vertical component of the wave activity flux (WAFz) standardized anomalies, averaged poleward of 40-80°N from 1 October 2008 - 31 March 2009.

Now look at Figure 12 below there are two more WAFz pulses after the MMW commences.  I include a longer polar vortex animation of begnning on December 1, 2020 in Figure vi.  The multiple WAFz pulses even post the MMW are creating a unique situation in the polar stratosphere this winter with polar stratospheric warmings on January 5th, January 15th and again February 2nd.  I don’t consider this “business as usual.” I would argue that the sudden stratospheric warmings of January 5th and possibly February 2nd should be to some degree two separate dynamic events and not simply one protracted event.  And as I will now explain considering them as two events helps us better understand the current weather and possibly better predict future weather, which cannot be done lumping everything as just one MMW with a central date of January 5th.

Figure vi. Observed 10 hPa geopotential heights (dam; contours) and temperature anomalies (°C; shading) across the Northern Hemisphere for 1 December 2020- 25 January 2021 and forecasted from 26  January – 9 February 2021.

I am sure at this point you are yelling at your computer screen “enough with the childlike wonderment and the academics” – let’s get down to tachlis (don’t get the wrong impression, I don’t speak a lick of Yiddish)  how does this impact me?  As I tried to argue in last week’s blog, we have a hybrid or amalgam of pre- and post- PV disruption weather all happening simultaneously.  We have observed/forecasts consistent with pre-PV disruption weather characterized by Ural blocking forcing cold and snow in East Asia, also cold and snow in  Western North America but mild in Europe and the Eastern US.  But we have observed/forecasts consistent with a post-PV disruption (and more what might be expected following a PV split and not a PV displacement though both have occurred) with Greenland blocking, cold and snow for Europe (including the UK this week) and milder in East Asia.  The one region that has cold and snow both before and after a PV disruption – Siberia has an exceptional cold streak so far this winter (see Philadelphia Inquirer).  Also, in the era of climate change to see cold and snow in just one of the three target regions – East Asia, Europe, Eastern US associated with PV disruptions is difficult enough, to see all three within a short time period is impressive in my opinion and again suggestive of an unusual weather pattern across the NH.

We don’t expect or not trained to Superman and Clark Kent or Batman and Bruce Wayne  in the same room at the same time but I think there are real world advantages to being open to the idea.  I think we will continue to see this unusual mix or hybrid of pre- and post-PV disruption weather or Superman and Clark Kent or Batman and Bruce Wayne present together. It does seem from Figure 12 that the heat flux may finally wane by early February, and the weather may finally follow a more common script following a PV disruption with more consistent cold in Europe and/or the Eastern US.  I still maintain that the GFS forecast (and this is not consistent across models, so confidence is low) with the PV centered over Svalbard, high pressure over Alaska and northerly, cross polar flow from Asia into Canada suggests cold temperatures for North America.  And as I argued in last week’s blog, I do believe that over time the cold should make its way into eastern North America even with the major or single PV center over Eurasia.  Also the latest CFS forecast for February (Figure 14) is consistent with my thinking but with the caveat the CFS has a checkered track record.

On Twitter and in last week’s blog I highlighted amplified warm/positive PCHs for this week (see Figure ii with downward arrow ending January 26th) arguing that it raises the risk of severe winter weather across the mid-latitudes this week and into next despite absence of such expectations in the models.  In Figure ii, I include another downward arrow for the second week of February.  It does not look as impressive as this week’s lower tropospheric spike in PCHs, but something to watch.

AO Blog Update | AER | Weather Risk Assessment

WWW.AER.COM

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January 25, 2021 - Dr. Judah Cohen from Atmospheric and Environmental Research (AER) embarked on an experimental process of regular research, review, and analysis of the Arctic Oscillation & Polar Vortex.

 

[sebastiaan1973]

The collapsed Polar Vortex is now tyring to reorganize over the Northern Hemisphere, but will face strong weather dynamics, as high-pressure systems persist

WWW.SEVERE-WEATHER.EU

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February weather will be very dynamic in United States and Europe, also because the Polar Vortex is trying to recover from the collapse

A story  by Recretos.

[Bricriu]

A story with not a great ending if it's deep cold into the UK and Ireland you're after.

[Don]

28 minutes ago, Bricriu said:

A story with not a great ending if it's deep cold into the UK and Ireland you're after.

Doesn't seem too bad to me for the UK and Ireland?

Edited January 27, 2021 by Don

[ICE COLD]

8 minutes ago, Don said:

Doesn't seem too bad to me for the UK and Ireland?

Yer that’s how I see it . Definitely will have opportunities next month for sure . Oh and theres still March

Edited January 27, 2021 by ICE COLD

[Bricriu]

38 minutes ago, Don said:

Doesn't seem too bad to me for the UK and Ireland?

"Europe is separated into two temperature regions, with colder air remaining more to the north and warmer to the south."

That to me just seems like more of the same, rather than any sustained cold spell taking hold. He holds out the possibility the MJO may tilt things in our favour, but its not a silver bullet either.

[Don]

4 minutes ago, Bricriu said:

"Europe is separated into two temperature regions, with colder air remaining more to the north and warmer to the south."

That to me just seems like more of the same, rather than any sustained cold spell taking hold. He holds out the possibility the MJO may tilt things in our favour, but its not a silver bullet either.

Exactly and that includes the UK and Ireland.  If you look at the temperature anomaly map it also shows the UK and Ireland firmly colder than average, albeit warmer temperatures are not far away, so probably indicates continued cold/mild battles for the UK and Ireland at times.  However, it's often the case in winter, if north/north west Europe is cold, south/south east Europe is mild and vice versa.  As always though, we will just have to wait and see.

[snowblizzard]

41 minutes ago, Bricriu said:

"Europe is separated into two temperature regions, with colder air remaining more to the north and warmer to the south."

That to me just seems like more of the same, rather than any sustained cold spell taking hold. He holds out the possibility the MJO may tilt things in our favour, but its not a silver bullet either.

Yes, the question is how far West towards UK & Ireland any cold pools can be convected and as we know it's a rare occurrence!

[Griff]

It's quiet in here, ecm zonal latest... 

[Don]

1 hour ago, Griff said:

It's quiet in here, ecm zonal latest... 

That gets the zonal wind back to normal faster than yesterday's update.

[Griff]

38 minutes ago, Don said:

That gets the zonal wind back to normal faster than yesterday's update.

True, but that's the PV strat rather than trop, initially?

[knocker]

On the sudden stratospheric warming and polar vortex of early 2021

Author: 

Michelle L'Heureux

·                  The POLAR VORTEX is coming!!!!!  That’s the ALL CAPS message these days in various news articles thanks due to the sudden stratospheric warming that occurred on January 5, 2021. We’re going to take a deeper look at the polar vortex and possible interactions with our ongoing La Niña. But, to recap previous articles on this blog:

·                  — The Polar Vortex doesn’t just appear randomly. The polar vortexes (more than one!) are a regular feature in the atmosphere, spinning away around the poles in both the Northern and Southern Hemispheres.

·                  — There is the stratospheric polar vortex, which is located in the layer that is 5-30 miles above Earth’s surface and only appears in winter (this is the focus of the Q&A below). Sometimes you might also hear about the tropospheric polar vortex, which is year-round and occupies the lowest layer of the atmosphere that touches the surface. 

·                  — Sudden Stratospheric Warmings (SSWs) are occasions in the winter (~6 times per decade), when the polar stratosphere warms and the winds that normally flow from west to east around the pole weaken dramatically and even reverse direction, corresponding to a breakdown of the polar vortex.

·                  — These SSWs can eventually cause the tropospheric jet stream to weaken, which allows cold air bottled up near the polar cap to escape and expand into the middle latitudes, such as the United States, Europe, and parts of Asia. The impacts on the surface are not guaranteed and they are not necessarily experienced everywhere. 

·                  Luckily, a great panel of scientific experts came together to answer our burning questions: Amy Butler at NOAA Chemical Sciences Lab, who has written two guest posts previously, Laura Ciasto at the NOAA Climate Prediction Center(previously blogging on Ultraviolet radiation) and Daniela Domeisen, who researches SSWs and surface impacts at ETH Zurich.

https://climate.gov/news-features/blogs/enso/sudden-stratospheric-warming-and-polar-vortex-early-2021

 

[sebastiaan1973]

Seems to me the downwelling is less good, as a couple of days ago was forecasted.

[Don]

2 hours ago, sebastiaan1973 said:

Seems to me the downwelling is less good, as a couple of days ago was forecasted.

Typical winter 2020/21!

[snowblizzard]

1 hour ago, Don said:

Typical winter 2020/21!

Steadily becoming the most frustrating of winters!  

[wellington boot]

On 25/01/2021 at 20:04, Griff said:

ECM zonal latest... 

Can you tell me why the red lines change between the charts? I understood these marked long term average, low and high, but they appear to change.

[bluearmy]

The SPV remains with a split forecast (vortices e of greeny  and far ne Siberia)

not the best for us and perhaps where the prediction of a strong Atlantic is based in the extended ??