sebastiaan1973
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Posts posted by sebastiaan1973
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Once again, extreme cold in NW-Russia and Scandinavia. Up to -36c. Cheers, a wodka please.
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For the first time a negative wind
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- Popular Post
- Popular Post
Incredible cold in Scandinavia and NW-Russia,
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192 vs 384h
You can see the difference, the winds are blowing from the opposite direction.
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Using the ERA5 reanalysis, sea surface temperature, sea ice observations, and the real-time multivariate Madden-Julian Oscillation (MJO) index, the evolution of the stratospheric extreme circulation in the winter of 2022/2023 is explored. The stratospheric polar vortex was disturbed three times in the 2022/23 winter, contrasted with only one disturbance during the other three recent winters with an SSW. Possible favorable conditions for the strong stratospheric disturbances and their effects on stratospheric ozone, water vapor distribution, and near-surface temperature were examined. Around 7 December 2022 when a short but strong pulse of planetary wavenumber 2 appeared from the troposphere to stratosphere, a weakened and elongated stratospheric polar vortex formed at 10 hPa. This pulse is related to the intensifying Ural ridge and the deepening East Asian trough. After the first stratospheric disturbance, a large fraction of cold anomalies occurred in the Eurasian continent. A lagged impact after these stratospheric disturbances was observed as strong cold anomalies formed in North America from 13 to 23 December. On 28 January 2023, a minor SSW event occurred due to a displacement of the stratospheric polar vortex. A strong pulse of eddy heat flux contributed alternately by planetary wavenumber 1 and 2 showed a large accumulative effect on the stratospheric disturbance. However, the downward impact of this second disturbance was weak, and cold surges were not noticeable after this minor SSW. The third stratospheric disturbance this winter is a major displace-type SSW that occurred on 16 February 2023, and the total eddy heat flux primarily contributed by planetary wavenumber 1 increased rapidly. Following the major SSW, the North American continent was covered by large patches of strong cold anomalies until the end of March. During the three disturbances, the residual circulation correspondingly strengthened. The water vapor and ozone in the middle and lower layers of the polar stratosphere showed positive anomaly disturbances, especially after the major SSW onset. The unprecedented frequent stratospheric disturbances in winter 2022/23 were accompanied by severe loss of Barents-Laptev Sea ice and anomalously cold tropical Pacific sea surface temperatures (La Niña), which have been reported to be conducive to the enhancement of planetary waves 1 and 2 respectively. Further, two weeks before the major SSW, existing MJO developed into phases 4–6, also contributing to the occurrence of major SSW.
Just a moment...
AGUPUBS.ONLINELIBRARY.WILEY.COM-
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Thanks Matt.
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Some cherrypicking. We see some 'wild charts' in GFS, not all of them delivering cold, but I see in these some uncommonly things happening.
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On 22/12/2023 at 00:46, Catacol said:
Hard to be certain…but one of the artefacts of CC is the northerly shunt of the sub tropical high pressure belt. When we combine this with a generally stronger stratospheric polar vortex (another consequence of CC caused by a cooling stratosphere) we have a more difficult envelope for high latitude ridges in winter. Pressure from the north in terms of the vortex and from the south in terms of a more obvious and intrusive Azores/Euro High suggests to me that we get less cold blocking and tropospheric forcing from the pacific is less reliable and dominant in shaping patterns. This is why I continue to think that we need the removal of one of these factors in order to achieve cold…and there is little sign of the Hadley Cell retreating….so that leaves the vortex. I have a totally unevidenced sense that CC might provide more frequent setups for SSWs to occur though we will need a much longer tale of the tape to be sure. So…in winters without a SSW we are really up against it to see a properly cold spell but when we get a SSW we are in the game…though admittedly an SSW is not a guarantee of anything and the 2018 style setup is unlikely to become common.
Our grandchildren may reflect on a U.K. context which sees properly cold spells in winter becoming a 1 in 10 year event. Sadly I’m not sure the direction of travel suggests anything other than this. I grew up in the 80s when cold spells were common. Those days - until something significant changes in the climate - are gone for now.
We definitely need AGC
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If we get a SSW the question is, what is the impact? Downwelling or not e.g.
Daniela Domeisen: The role of North Atlantic-European weather regimes in the surface of SSW events.
It seems to matter what the tropospheric setting is at day 0.
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1 hour ago, Mike Poole said:
I posted this several times...
http://arctic.som.ou.edu/tburg/products/realtime/strat/100mb_vortex.php
The representation of the stratosphere and stratosphere–troposphere coupling processes is evaluated in the subseasonal Global Ensemble Forecast System, version 12 (GEFSv12), hindcasts. The GEFSv12 hindcasts develop systematic stratospheric biases with increasing lead time, including a too strong boreal wintertime stratospheric polar vortex. In the tropical stratosphere, the GEFSv12 winds and temperatures associated with the quasi-biennial oscillation (QBO) tend to decay with lead time such that they underestimate the observed amplitudes; consistently, the QBO-associated mean meridional circulation is too weak. The hindcasts predict extreme polar vortex events (including sudden stratospheric warmings and vortex intensifications) about 13–14 days in advance, and extreme lower-stratospheric eddy heat flux events about 6–10 days in advance. However, GEFSv12’s ability to predict these events is likely affected by its zonal-mean circulation biases, which increases the rates of false alarms and missed detections. Nevertheless, GEFSv12 shows stratosphere–troposphere coupling relationships that agree well with reanalysis and other subseasonal forecast systems. For instance, GEFSv12 reproduces reanalysis relationships between polar vortex strength and the Northern Annular Mode in the troposphere. It also exhibits enhanced weeks 3–5 prediction skill of the North Atlantic Oscillation index when initialized during strong and weak polar vortex states compared to neutral states. Furthermore, GEFSv12 shows significant differences in Madden–Julian oscillation (MJO) amplitudes and enhanced MJO predictive skill in week 4 during easterly versus westerly QBO phases, though these results are sensitive to the level used to define the QBO. Our results provide a baseline from which future GEFS updates may be measured.-
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Almost the same output as yesterday. Look at the lowest average, around 5 m/s
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Just now, Uncertainty said:
Are you saying the eps are showing a mean reversal Nick? That would be quite something. And am I right in saying that the the 46 is now fundamentally a separate model and won’t necessarily follow on from the eps?
Whatever the GEFS are doing on the strat isn’t stopping them producing an eye catching block in the trop mind!
Yes, these are two seperate models.
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45 minutes ago, Andy8472 said:
http://arctic.som.ou.edu/tburg/products/realtime/strat/100mb_vortex.php
The representation of the stratosphere and stratosphere–troposphere coupling processes is evaluated in the subseasonal Global Ensemble Forecast System, version 12 (GEFSv12), hindcasts. The GEFSv12 hindcasts develop systematic stratospheric biases with increasing lead time, including a too strong boreal wintertime stratospheric polar vortex. In the tropical stratosphere, the GEFSv12 winds and temperatures associated with the quasi-biennial oscillation (QBO) tend to decay with lead time such that they underestimate the observed amplitudes; consistently, the QBO-associated mean meridional circulation is too weak. The hindcasts predict extreme polar vortex events (including sudden stratospheric warmings and vortex intensifications) about 13–14 days in advance, and extreme lower-stratospheric eddy heat flux events about 6–10 days in advance. However, GEFSv12’s ability to predict these events is likely affected by its zonal-mean circulation biases, which increases the rates of false alarms and missed detections. Nevertheless, GEFSv12 shows stratosphere–troposphere coupling relationships that agree well with reanalysis and other subseasonal forecast systems. For instance, GEFSv12 reproduces reanalysis relationships between polar vortex strength and the Northern Annular Mode in the troposphere. It also exhibits enhanced weeks 3–5 prediction skill of the North Atlantic Oscillation index when initialized during strong and weak polar vortex states compared to neutral states. Furthermore, GEFSv12 shows significant differences in Madden–Julian oscillation (MJO) amplitudes and enhanced MJO predictive skill in week 4 during easterly versus westerly QBO phases, though these results are sensitive to the level used to define the QBO. Our results provide a baseline from which future GEFS updates may be measured.-
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1 hour ago, Catacol said:
Anyone know what's happened to the archive charts? Mine on NetW and also Meteociel won't load. I'm wanting to go back and look at SSW precursor patterns around 3-4 weeks ago....
This an archive https://www.wetterzentrale.de/nl/reanalysis.php?model=cfsr
From 1979 till the present day.
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Tweet by World Climate Service.
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In comparison with the last days.
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34 minutes ago, Catacol said:
Except it didn't in November when the IOD was even stronger. There are layers within layers going on here that I think are not understood. I messaged Eric Webb recently to get his thoughts on the MJO passage and pacific situation and he didn't come back. Why would he? 2 reasons. He couldn't be bothered to reply to one of many turgid requests. No issue with that tbh. We all get too many messages. Or...and I put my request relatively cogently I think, he is not prepared to take a stab at what impacts on such a variable forecast of pacific conditions, so important for sub tropical windflows and patterns, because even he is vague on it. I note he works a lot off ensembles.
I wish there was a coherent archive of pacific patterns going back as many years as we now have synoptic charts. Does anyone know of an MJO archive anywhere? I'd love to see whether my sense of failed cycles at crucial points of the core winter season has any basis in fact or whether I'm seeing things. I'd also love to get some statistical data on the link between phases and blocking or westerly patterns. I know we have the composite charts, but they are averages. And without the MJO data it is difficult to get setups to analyse. I want to be able to pull up a Hovmoller, RMM or something similar and sit it against a northern hemisphere synoptic chart at 1, 2 and 3 week lags and do some old fashioned police work!
You mean this one: http://www.bom.gov.au/climate/mjo/
E.g.
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Well in terms of analogy there is nothing wrong with december 2023. This is a composed pressure anomaly for el nino & positive IOD. We see lower in the N. Higher in the north.
The MJO-passage suffered from the IOD - I guess-. This is knowledge we could have known on forehand.
An important study is this one.
https://rmets.onlinelibrary.wiley.com/doi/10.1002/asl.1005
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At 50 hPa it seems the polar vortex moves to Siberia. Should this increase the opportunities for 'us' (lovers of ice/ snow etc) I think so.
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Thanks to Gerhard.
https://www.climate.gov/news-features/blogs/polar-vortex/welcome-polar-vortex-blog
We are excited to announce that NOAA Climate.gov, home of the highly popular ENSO Blog, is venturing into a colder, darker, and windier corner of the atmosphere with the new Polar Vortex Blog. We plan to explore various facets of the winds, climate, and chemistry within the fascinating region of the atmosphere known as the polar stratosphere, and explain how this region can sometimes drive big changes in our weather patterns!
While ENSO may be the seasoned celebrity in the seasonal forecasting world, in recent years the stratospheric polar vortex has become a rising star: constantly making headlines and being stalked by the paparazzi, but often misunderstood or misrepresented. We hope to clear up misconceptions, highlight new research, and discuss what the polar vortex is up to and how it may affect our winter’s weather. We expect there to be 1-2 posts per month between December and March, with the initial focus on the Northern Hemisphere polar vortex (yep, there’s one down south, too!).
So who’s on the team?
Amy Butler is a research scientist at the NOAA Chemical Sciences Laboratory and an expert on the stratosphere and its influence on weather;
Laura Ciasto is a meteorologist at the NOAA Climate Prediction Center. She leads the development of stratospheric and teleconnection forecast products, but is also a Week 3-4 forecaster (NOAA’s description for forecasts of weather conditions 3-4 weeks in the future);
The Climate.gov graphics and data visualization team and managing editor, Rebecca Lindsey, with the NOAA Climate Program Office.
While we [Amy & Laura] are the lead editors of the blog, we hope to have guest contributors who can share their own perspectives and research on the polar vortex and related topics. And of course, this blog will not succeed without active engagement from you, our readers. We are happy to hear your constructive feedback and suggestions, and are excited to engage with you on this topic!
After reading this introduction, the first question you might have is likely: What is the polar vortex? And so, that’s where we’ll begin!!
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The representation of the stratosphere and stratosphere–troposphere coupling processes is evaluated in the subseasonal Global Ensemble Forecast System, version 12 (GEFSv12), hindcasts. The GEFSv12 hindcasts develop systematic stratospheric biases with increasing lead time, including a too strong boreal wintertime stratospheric polar vortex. In the tropical stratosphere, the GEFSv12 winds and temperatures associated with the quasi-biennial oscillation (QBO) tend to decay with lead time such that they underestimate the observed amplitudes; consistently, the QBO-associated mean meridional circulation is too weak. The hindcasts predict extreme polar vortex events (including sudden stratospheric warmings and vortex intensifications) about 13–14 days in advance, and extreme lower-stratospheric eddy heat flux events about 6–10 days in advance. However, GEFSv12’s ability to predict these events is likely affected by its zonal-mean circulation biases, which increases the rates of false alarms and missed detections. Nevertheless, GEFSv12 shows stratosphere–troposphere coupling relationships that agree well with reanalysis and other subseasonal forecast systems. For instance, GEFSv12 reproduces reanalysis relationships between polar vortex strength and the Northern Annular Mode in the troposphere. It also exhibits enhanced weeks 3–5 prediction skill of the North Atlantic Oscillation index when initialized during strong and weak polar vortex states compared to neutral states. Furthermore, GEFSv12 shows significant differences in Madden–Julian oscillation (MJO) amplitudes and enhanced MJO predictive skill in week 4 during easterly versus westerly QBO phases, though these results are sensitive to the level used to define the QBO. Our results provide a baseline from which future GEFS updates may be measured. Evaluation of Processes Related to Stratosphere–Troposphere Coupling in GEFSv12 Subseasonal Hindcasts in: Monthly Weather Review Volume 151 Issue 7 (2023) (ametsoc.org)
https://journals.ametsoc.org/view/journals/mwre/151/7/MWR-D-22-0283.1.xml
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The importance of the polar vortex at 100 hPa by Simon Lee
The most commonly-used diagnostic of the strength of the stratospheric polar vortex is the zonal-mean zonal wind at 10 hPa (~30 km) and 60°N (U10-60), which is westerly during winter. It is an easy diagnostic to compute and understand, which probably helped drive its uptake. Reversals of U10-60 to easterlies indicate either a major sudden stratospheric warming (SSW) if they occur during midwinter, or the final stratospheric warming (and the transition to the summertime state) if they occur in spring. U10-60 has also been used to diagnose strong polar vortex events, sometimes taken to be when the winds exceed 40 m/s (this is not quite as strictly defined as SSWs, it must be said).
10 hPa is, however, about 20 km above the tropopause, while the polar vortex is very much a 3-dimensional phenomenon. Condensing it into a single diagnostic is rooted in solid dynamics, but is far from the only part of the story — particularly when it comes to interpreting the influence of the vortex strength on tropospheric weather patterns. Perhaps due to the availability of forecast plots, or the translation of information from academia to forecasters and the public* (which I try to contribute to as best I can), the importance of the lower stratosphere is often overlooked. That’s what this blog is about.
This year is the 20th anniversary (!) of the publication of “Stratospheric Memory and Skill of Extended-Range Weather Forecasts” in Science, by Mark Baldwin et al. It is one of the key stratosphere-troposphere coupling papers that helped establish the role of the stratospheric polar vortex in tropospheric weather and climate prediction. In the paper, Baldwin et al. compute the “e-folding timescale” of the Northern Annular Mode (NAM) as a function of pressure level and time of year. The NAM in the stratosphere is effectively the strength of the polar vortex and well-correlated with the zonal winds at 60°N. The e-folding timescale is just the time taken for the autocorrelation of the NAM index to decay to 1/e (about 0.37), which is a measure of the persistence of the NAM.
They showed that, during winter (mainly December to February), the timescale of the NAM maximises in the lower stratosphere at around 100-150 hPa. Its e-folding timescale peaks at over four weeks. In contrast, up at 10 hPa, the NAM timescale is much shorter during winter — two-to-three weeks. Above that, toward the stratopause, it’s even shorter (a few days; not shown in their paper). Baldwin et al. also demonstrated that the timescale of the tropospheric NAM peaks at the same time as the peak in the lower stratosphere, which would be expected from a downward influence. (They also showed that the lower-stratospheric NAM can predict the surface NAM better than the surface NAM predicts itself, confirming its utility.) Figure 1 here shows something similar to Figure 1a in the Baldwin et al. paper, but just for 100 and 1000 hPa. Note how the long timescales are not fully developed in November-December, which is important for thinking about any early-winter coupling.
Figure 1: Timescale of the NAM at 100 hPa (red) and 1000 hPa (black) following a similar method to Baldwin et al. 2003 (Science), but the NAM is here computed as EOF1 of zonal mean geopotential height poleward of 20°N (following Baldwin and Thompson 2009, QJ).
Given all that, it’s then perhaps not surprising that myriad subsequent studies have reported that the lower stratosphere plays a key role in whether or not an SSW strongly influences surface weather patterns. Back in 2009, Ed Gerber et al. stated:
Furthermore, not all SSW events are created equal; a sharp reversal of the zonal winds at 10 hPa does not guarantee deep penetration through the stratosphere, and it is the lower stratosphere that appears to influence the troposphere.
More recently, Ian White et al. (2020) demonstrated a remarkably “generic” linear response of the troposphere to the 100 hPa circulation anomalies following SSWs. Hilla Afargan-Gerstman et al. (2022) also pointed out that spread in the lower-stratospheric anomalies post-SSW dominate spread in the Atlantic jet response. (This is not an exhaustive list of such studies.)
Therefore, perhaps the best way to think about it is that anomalous vortex states at 10 hPa can serve as a predictor of anomalous vortex states at 100 hPa, which themselves then “tickle the troposphere” (as Kushner and Polvani 2004 so delightfully described it) almost instantaneously.
Thus, a large fraction of instances when the stratosphere is purportedly in a different state to the troposphere, or somehow not influencing the troposphere, stem from looking at diagnostics 20 km above the troposphere. Rather, one should first consider whether large circulation anomalies are present in the lower stratosphere, below 10 hPa, for a more complete understanding. It is rare to see large circulation anomalies in the lower stratosphere opposing the tropospheric state: see, for example, the weather regime probabilities computed using 100 hPa 60°N zonal wind anomalies in Charlton-Perez et al. 2018, or my paper from the following year.
In fact, December 2022 (Figure 2) provides a nice example of when the bottom half of the vortex — below 10 hPa — was weak (negative NAM), while the top half was neutral or strong. A major SSW occurred on 16 February, but only coupled down to the troposphere once the vortex below 50 hPa finally weakened — which took place following a second burst of wave activity and deceleration in late February. The coupling was brief, as the vortex recovered quite quickly thereafter.
Figure 2: time-height cross-section of the NAM during winter 2022-2023. See here for more information.
All this brings me to where we are at present, on 23 November 2023. Up at 10 hPa, the vortex is currently unusually strong, with U10-60 close to 40 m/s (about 10 m/s above climatology). Figure 3 shows how this has evolved over the last 60 days. But, in addition to it being early in the season — when the vortex is not as well-developed in the lower stratosphere — the bottom half of the vortex is being bashed around by a surge in upward-propagating wave activity (Figure 4). Thus, in this case, the lower stratospheric vortex weakens first, as Figure 3 shows. The rapid loss of the strong vortex from the bottom half of the stratosphere is then favourable for Greenland blocking/negative tropospheric NAM regimes to develop, which is what forecasts are increasingly suggesting. This could be thought of more as a “feedback”, perhaps, than the downward propagation typically seen post-SSW.
Although the timescale at 100 hPa is long, a large contributor to that comes from events that encompass the entire vortex. In this case, if the upper stratospheric vortex remained strong, it would likely erode the weak vortex anomalies in the lower stratosphere. Some forecasts, such as ECMWF’s extended-range suggest the 10 hPa vortex will weaken (this system has been predicting a weak 10 hPa vortex by mid-December since late October). If that were to happen, to understand how that would influence the troposphere, we’d need to then be once again looking at the extent to which the anomaly reaches the lower stratosphere.
To summarise, (also, hello to everyone who skipped to the end), I am not suggesting one should abandon 10 hPa as a diagnostic for how the vortex is behaving. But, for interpreting the extent of coupling to the troposphere, one should first consider the state of the vortex just above the tropopause. Looking at 10 hPa and 1000 hPa and noting they are in apparent disagreement neglects the dynamics of the 30 km of atmosphere between them.
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Autumn & Winter 2023---2024 Stratospheric Polar Vortex. Events, Analysis, Discussions AND Outlooks
in Spring Weather Discussion
Posted
I think this is a consequence of negative AO developing.