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ENSO modulation of the QBO: Results from MIROC models with and without non-orographic gravity wave parameterization

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Abstract

Observational studies have shown that, on average, the quasi-biennial oscillation (QBO) exhibits a faster phase progression and shorter period during El Niño than during La Niña. Here, the possible mechanism of QBO modulation associated with ENSO is investigated using the MIROC-AGCM with T106 (~1.125°) horizontal resolution. The MIROC-AGCM simulates QBO-like oscillations without any non-orographic gravity wave parametrizations. A 100-year integration was conducted during which annually repeating sea surface temperatures based on the composite observed El Niño conditions were imposed. A similar 100 year La Niña integration was also conducted. The MIROC-AGCM simulates realistic differences between El Niño and La Niña, notably shorter QBO periods, a weaker Walker circulation, and more equatorial precipitation during El Niño than during La Niña. Near the equator, vertical wave fluxes of zonal momentum in the uppermost troposphere are larger and the stratospheric QBO forcing due to interaction of the mean flow with resolved gravity waves (particularly for zonal wavenumber ≥ 43) is much larger during El Niño. The tropical upwelling associated with the Brewer–Dobson circulation is also stronger in the El Niño simulation. The effects of the enhanced tropical upwelling during El Niño are evidently overcome by enhanced wave driving, resulting in the shorter QBO period. The integrations were repeated with another model version (MIROC-ECM with T42 horizontal resolution) that employs a parameterization of non-orographic gravity waves in order to simulate a QBO. In the MIROC-ECM the average QBO periods are nearly identical in the El Niño and La Niña simulations.

https://journals.ametsoc.org/doi/abs/10.1175/JAS-D-19-0163.1?af=R#.XajQ0wIFees.twitter

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Some further notes on the QBO that may be of interest (or not of course)

Role of Quasi-Biennial Oscillation in Coupling Process

In the tropical stratosphere, the dominant form of variability is a quasi-periodic (2-3-year) wave-driven descending zonal mean wind reversal, called the quasibiennial oscillation (QBO). The period of the QBO at any level varies from 2 to 3 years, and it could probably be predicted for about 1 year. The QBO is observed to affect the global stratospheric circulation. It modulates a variety of tropical and extratropical phenomena including the strength and stability of the wintertime polar vortex, and the distribution of ozone and other gases (Baldwin et al. 2001).  Figure 9.5 illustrates the schematic picture of the dynamical overview of the QBO during northern winter (Baldwin et al. 2001). In the tropics, the stratospheric QBO is driven by the upward propagating gravity, inertia gravity, and Kelvin and Rossby gravity waves. In the middle and high latitudes, it is maintained by the planetary-scale waves. The contours in the tropics are similar to the observed wind values when the QBO is easterly. It can be seen that the QBO extends to the mesospheric region and even above 80 km.

The QBO is driven by the dissipation of a variety of equatorial waves and gravity waves that are primarily forced by deep cumulus convection in the tropics.  The stratospheric QBO effects extend to Earth’s surface during northern midwinter.  There is also observational evidence that the QBO modulates the depth of the troposphere in the tropics and subtropics, affecting convection, monsoon circulations, and hurricanes.

Although the amplitude of the QBO decreases rapidly away from the equator, observations and theory show that the QBO affects a much larger region of the atmosphere.  Through wave coupling, the QBO affects the extratropical stratosphere during the winter season, especially in the northern hemisphere where planetary wave amplitudes are large. These effects also appear in constituents such as ozone. In the high-latitude northern winter, the QBOs modulation of the polar vortex may affect the troposphere through downward penetration. Tropical tropospheric observations show intriguing quasi-biennial signals which may be related to the stratospheric QBO. The QBO has been linked to variability in the upper stratosphere, mesosphere, and even ionospheric F layer (see Fig. 9.5).

qbo.thumb.JPG.2434bae5e9e76784fdcfb0a4439eedf1.JPG

Source: K. Mohanakumar, "Stratosphere Troposphere Interactions

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Effects of the QBO in the Stratosphere and Mesosphere

Although the QBO is observed to be confined to within about 25° north and south of the equator, its effects extend throughout the stratosphere (Naito and Hirota 1997).  Coupling to the extratropical stratosphere is understood to depend on the modulation of planetary-scale waves. During the winter season, when stratospheric winds are strong and westerly, planetary-scale waves propagate upward from the troposphere and are refracted equatorward in the stratosphere, depending on the structure of the zonal mean wind field. By modulating the direction and reflection/absorption of the planetary scale waves, the QBO induces a remote effect at high latitudes in winter, especially in the northern hemisphere where planetary-scale waves are largest. The effect of the annual cycle of planetary wave propagation, together with the QBO’s effect, is observed to modulate dynamical quantities, such as temperature, winds, wave amplitudes, potential vorticity as well as chemical constituents like, ozone, nitrogen dioxide (Zawodny and McCormick 1991), aerosols, water vapor, and methane. The QBO’s influence is seen in subtropical ozone variability during the winter-spring season in both hemispheres.

Effects of the QBO may also be seen at the stratopause where the descending westerly phases of the stratopause semiannual oscillation are strongly influenced by the underlying QBO. Near the mesopause, observations show a well-defined QBO, which may be driven by the selective filtering of small-scale gravity waves by the underlying winds they traverse. Chen and Robinson (1992) documented a statistical link between the phase of the QBO and the ionospheric equatorial ionization anomaly. A mechanism was proposed in which the planetary waves modulate the tidal wind, and by means of the dynamo effect, change electric fields in the E region, which can be transferred to the F region along geomagnetic field lines to cause variations in the equatorial ionization anomaly.

9.4.2 QBO Effects on the Troposphere

The QBO’s effects on the troposphere are suggestive, but are not well understood.  Gray (1984) has demonstrated an intriguing and significant link between the phase of the QBO and hurricane formation. The equatorial troposphere shows variability on the timescale of the QBO, but a direct link to the stratospheric QBO has not been established. It is possible that the QBO may influence the high-latitude northern troposphere through its effect on the stratospheric polar vortex. Coupling between stratospheric zonal mean wind and the mid-tropospheric North Atlantic oscillation is strong, but the cause and effect are not clear. It is possible that QBO-induced high-latitude wind anomalies penetrate downward into the troposphere (Gray 2003;

Gray et al. 2004).

9.4.3 Stratospheric QBO and Tropospheric Biennial Oscillation

Signals of biennial oscillations with periods ranging from 20 to 32 months are noted in the tropospheric temperature over the tropics (Sathiyamurthy and Mohanakumar 2002). The phase of the tropospheric biennial oscillation (TBO) in temperature does not vary with height from surface to the level of tropopause and is found to be associated with the intensity of the monsoon rainfall. Temperature over the tropical region shows Quasi-Biennial Oscillation (QBO) in lower stratosphere. Phases of the QBO and TBO in temperature meet at tropopause level (see Fig. 9.6). Where they meet, phases of the QBO and TBO are unsynchronized during the decade 1971-1981 and synchronized during next decade, 1982-1992. The QBO in zonal wind has neither interdecadal variability nor disturbances.

Source: K. Mohanakumar, "Stratosphere Troposphere Interactions

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Some very brief notes on transport processes in the Stratosphere and Troposphere

Introduction

Transport of air across the tropopause plays an important role in determining the chemical composition, and hence radiative properties, of both the troposphere and stratosphere. Quantifying this transport presents a significant challenge on account of the many multiscale processes involved from the global scale mean meridional circulation, through intermediate advective and convective processes, to molecular diffusion. It has long been recognized that tropospheric air enters the stratosphere principally in the tropics, and moves poleward in the stratosphere.  To understand the large-scale circulation in the troposphere and stratosphere, it is useful to look at transport processes averaged around a latitude circle. Ozone production mainly takes place in the tropical stratosphere as the direct solar radiation photodissociates oxygen molecules (02) into oxygen atoms (0), which quickly react with other 02 molecules to form ozone (03). But most ozone is found in the higher latitudes rather than in the tropics, i.e., outside of its natural tropical stratospheric source region. This higher-latitude ozone results from the slow atmospheric circulation that moves ozone from the tropics where it is produced into the middle and polar latitudes. This slow circulation is known as the Brewer-Dobson circulation.

7.2 The Brewer-Dobson Circulation

Figure 7.1 shows the zonally averaged circulation in the middle atmosphere superimposed on top of an annual average ozone density. The Brewer-Dobson circulation is represented by the thick arrows. The figure also shows the seasonally averaged ozone density from north pole to south pole.

The Brewer-Dobson circulation is a slow circulation pattern, first proposed by Brewer to explain the lack of water in the stratosphere. He presumed that water vapor is freeze-dried as it moves vertically through the cold equatorial tropopause (see Fig. 7.1). Dehydration can occur in this region by condensation and precipitation as a result of cooling to temperatures below 193 K. The lowest values of water are found just near the tropical tropopause. Later Dobson suggested that this type of circulation could also explain the observed high ozone concentrations in the lower stratosphere polar regions which are situated far from the photochemical source region in the tropical middle stratosphere. The Brewer-Dobson circulation additionally explains the observed latitudinal distributions of long-lived constituents like nitrous oxide and methane.

This conceptual model has since been refined but not drastically altered. That Brewer-Dobson circulation is controlled by stratospheric wave drag, quantified by the Eliassen-Palm flux divergence, sometimes lays claim to the extratropical pump (as shown in Fig. 7.2), with the circulation at any level being controlled by the wave drag above that level. However, the wave drag can be difficult to compute accurately and it is common to diagnose the mean circulation from the diabatic heating. It is possible to estimate the net mass flux across a given isentropic surface from the diabatic heating.

On the other hand, transport of material along isentropic surfaces, such as that between the tropical upper troposphere and the lowermost stratosphere, is more difficult to quantify, especially the net transport of a given species that results from the two-way mixing. Observations show that the composition of the lowermost stratosphere varies with season, and suggest a seasonal dependence in the balance between the downward transport of air of stratospheric character and the horizontal transport of air of upper-troposphere character. For any time period, the integrated mass flux to the troposphere at middle and high latitudes is the sum of the mass flux across the 380 K potential temperature surface, the net mass transported between the tropical upper troposphere and the lowermost stratosphere, plus (minus) the mass decrease (increase) of the lowermost stratosphere (Appenzeller et al. 1996).  The first quantity is easy to compute, but the last two quantities are sensitive to small-scale processes, including synoptic-scale disturbances and convection.  The classical picture of the stratosphere-troposphere coupling has evolved over the last few years. Such developments and tuning are essential for a good description of processes that are important for the stratosphere-troposphere coupling.

zonal.thumb.JPG.eac1a3fae113677cbfc67780c79dbdee.JPGtransport.thumb.JPG.18c23f76e7fbf597760d56060a584130.JPG

Source: K. Mohanakumar, "Stratosphere Troposphere Interactions

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1 hour ago, knocker said:

Some further notes on the QBO that may be of interest (or not of course)

(SNIPPED)

Thanks for the above extracts and the ENSO/QBO paper Knocker. It's a shame that both are behind paywalls (so I assume you've paid?). The Mohanakumar work looks very good, all 400 pages of it, although I can only freely view the index. I see he's a Strat scientist who does a lot of work for the Freie University Berlin, whose excellent charts are frequently used in the Strat thread.

I'm looking at the current eQBO descent 'stall' as a possible next post. It appears that the strength of the westerly shear stress around 40hPa seems to be interfering with downward propagation. Rossby waves behind this, as per the 2016 failed eQBO? It would be great to get a discussion going on here.

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5 minutes ago, Blessed Weather said:

Thanks for the above extracts and the ENSO/QBO paper Knocker. It's a shame that both are behind paywalls (so I assume you've paid?). The Mohanakumar work looks very good, all 400 pages of it, although I can only freely view the index. I see he's a Strat scientist who does a lot of work for the Freie University Berlin, whose excellent charts are frequently used in the Strat thread.

I'm looking at the current eQBO descent 'stall' as a possible next post. It appears that the strength of the westerly shear stress around 40hPa seems to be interfering with downward propagation. Rossby waves behind this, as per the 2016 failed eQBO? It would be great to get a discussion going on here.

It's a little premature to talk of a stall, I think. As the Berlin QBO site says itself:

Quote

the transition to easterlies is often delayed between 30 and 50 hPa;

 

 

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35 minutes ago, Blessed Weather said:

Thanks for the above extracts and the ENSO/QBO paper Knocker. It's a shame that both are behind paywalls (so I assume you've paid?). The Mohanakumar work looks very good, all 400 pages of it, although I can only freely view the index. I see he's a Strat scientist who does a lot of work for the Freie University Berlin, whose excellent charts are frequently used in the Strat thread.

I'm looking at the current eQBO descent 'stall' as a possible next post. It appears that the strength of the westerly shear stress around 40hPa seems to be interfering with downward propagation. Rossby waves behind this, as per the 2016 failed eQBO? It would be great to get a discussion going on here.

No I haven't paid but I don't know who has access to papers on here via academic institutions/libraries. etc. Yes the book is excellent, if rather expensive when I bought it, but I freely admit much of it is way above my pay grade 🙂

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1 hour ago, Yarmy said:

It's a little premature to talk of a stall, I think. As the Berlin QBO site says itself:

 

 

Thanks Yarmy. You're right, I'm getting ahead of myself in thinking there's anything unusual as yet about the rate of descent. I should wait until Berlin start producing their stratosphere charts again on Nov 1st and keep an eye out for any unusual developments with the zonal winds over and near the equator.

Maybe the word stall is a bit strong at this stage, but as the link says, it's not unusual for the descent of easterlies to be "delayed" between 30 and 50hPa. There is a paper about QBO descent rates here, but it's a heavy read. Easterlies descend fastest between May and July because planetary waves are at their weakest, then descent slows as the planetary wave forcing increases.

I'm fascinated by the failed easterly QBO in 2015/16 and there's a research paper suggesting there might be more frequent occurrences in a warming climate. The paper abstract can be read here, but unfortunately the full paper is behind a paywall.

In the meantime, here's a good read about the failed descent:

The anomalous change in the QBO in 2015–2016
Abstract:
The quasi‐biennial oscillation (QBO) is a tropical lower stratospheric, downward propagating zonal wind variation, with an average period of ~28 months. The QBO has been constantly documented since 1953. Here we describe the evolution of the QBO during the Northern Hemisphere winter of 2015–2016 using radiosonde observations and meteorological reanalyses. Normally, the QBO would show a steady downward propagation of the westerly phase. In 2015–2016, there was an anomalous upward displacement of this westerly phase from ~30 hPa to 15 hPa. These westerlies impinge on or “cutoff” the normal downward propagation of the easterly phase. In addition, easterly winds develop at 40 hPa. Comparisons to tropical wind statistics for the 1953 to present record demonstrate that this 2015–2016 QBO disruption is unprecedented.

Full paper: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL070373

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Arctic Oscillation (AO) – The influence of Snow Cover Extent (SCE) and the Snow Advance Index (SAI)

We are now in the last 10 days of October and it’s a good time to look at the scientific research and findings that make the status of the SCE, but more particularly the SAI, important to UK/Europe winter prospects through their influence on the AO.

But first, why is the AO important to UK/European winters prospects? Simply put, when the AO is in its positive phase strong winds circulate around the Pole and confine colder air to polar regions. In the negative phase these winds weaken and the Jet Stream meanders, which allows an easier southward penetration of colder, arctic air. Here’s an illustration of the positive and negative modes:

1783487766_AOillustration.thumb.jpg.4292395474556c6356beb8dff7116090.jpg
Source: https://nsidc.org/cryosphere/icelights/2012/02/arctic-oscillation-winter-storms-and-sea-ice

In the winter of 2009/10 the mean AO during DJF was the lowest observed since at least 1950 and this became the subject of research by Dr Judah Cohen et al and the paper Winter 2009–2010: A case study of an extreme Arctic Oscillation event was published in late 2010:

This graph shows the 2009/10 negative mean AO (note NOAA use JFM rather than DJF):

2126127521_AOIndexJFM3-mthmean.thumb.jpg.b13ee85b4073c1b30795a97afd8d7935.jpg
Source: https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/JFM_season_ao_index.shtml

Dr Cohen's report concludes:

“The dominant NH winter [AO] circulation pattern can be shown to have originated with a two‐way stratosphere‐troposphere interaction forced by Eurasian land surface and lower tropospheric atmospheric conditions during autumn…..
The forcing was caused by:
“….a rapid advance in Eurasian SCE and persistently extensive snow cover that supported below normal temperatures and a strengthened Siberian high.”

Cohen and colleagues demonstrated that a statistically significant relationship exists between snow cover extent and lower tropospheric anomalies across Northern Eurasia as shown in the following charts:

Long-term correlation SAI and AO: 547133137_CorrelationSAIandDJFAO.thumb.jpg.dcefd968e5f1543c49c7695ed3980397.jpg

Correlation between AO and then SAI with Surface Level Pressure: 367146134_CorrelationSAIandDJFAOwithSLP.thumb.jpg.6a1135fec4ebf08c67805ea3b332d9f8.jpg

The report identified a six‐step process starting with a rapid advance in Eurasian snow cover and culminating in a negative surface AO. The six steps in sequential order are:

  1. rapid advance of Siberian snow cover in October,
  2. a strengthened Siberian high with colder than normal temperatures and higher sea level pressure (SLP) anomalies,
  3. increased upward Eliassen Palm flux or wave activity flux,
  4. a stratospheric warming,
  5. downward propagation of the associated height and wind anomalies from the stratosphere down to the surface and finally a negative surface AO.

The report noted that snow cover extent was well below normal across Eurasia the first week of October 2009, but during the last three weeks of October the SCE rapidly advanced. This led to the 2011 follow-up research by Dr Cohen that established that it appeared to be the rate of growth in snow cover during October that was more important than the mean cover for the month. The paper was titled: A new index for more accurate winter predictions.

Some extracts:

“….observational studies have established a statistically significant link between fall snow cover extent (SCE) and the winter AO and numerical modelling experiments forced with varying Eurasian SCE, reproduce an atmospheric AO response in winter similar to the observations. However during October 2009 it was not the mean SCE that was exceptional but rather the rapidity of the snow cover advance that was exceptional.

An important question that we have not answered is why the October SAI is more highly correlated with the DJF AO than the October SCE index. One likely reason is that the SAI is limited to latitudes equatorward of 60°N while the SCE index includes all of Eurasia, which has a significant amount of snow cover north of 60°N. Assuming that the high albedo of snow cover is one if not the most important snow characteristic that influences the overlying atmosphere, this would favour the SAI, which is limited to regions that are exposed to a higher sun angle more so than the SCE, in predicting the atmospheric response to snow cover variability. Another possibility is that the SAI is sensitive to the timing of snowfall, where snowfall at the end of the month contributes to higher values of the SAI and snowfall at the beginning of the month contributes to lower SAI values while the monthly‐mean SCE is insensitive to the timing of snowfall."

Dr Cohen acknowledged that more in-depth research is required to understand better why SAI is more important than SCE.

SCE and SAI - Current Situation:

In his 17th Oct blog Dr Cohen noted:

"At the time of the last blog October Siberian snow cover extent was off to a fast start but.... has experienced a prolong pause in advancing.  Still I expect that Eurasian snow cover extent will be above normal for the month of October.  But the magnitude of the positive anomaly does not look to be impressive at this point.  Slightly above normal snow cover extent is an indicator of a cold winter in the Eastern US, East Asia and Northern Europe but not a strong indication."
Source: https://www.aer.com/science-research/climate-weather/arctic-oscillation/

But Dr Cohen in a tweeted update on the 20th Oct:

"Siberian snow cover extent was knocked all down but it finally picked itself off the mat this weekend. I expect snow cover to steadily advance at a near normal pace for the remainder of October based on GFS forecasts."
Source: Twitter @judah47

Latest Forecasts:

Here’s the latest GEFS forecasts for the AO over the next 7, 10 and 14 days showing the AO remaining negative into early November:

170253597_AOGEFSforecasts22Oct2019.thumb.jpg.32f099ba047acb5cb4580d9a6f985e57.jpg
Note: The ensemble mean forecasts of the AO index are obtained by averaging the 11 GFS ensemble members and the observed AO index (black line) is superimposed on each panel for comparison. The yellow shading shows the ensemble mean plus and minus one standard deviation among the ensemble members.
Source: https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao_index_ensm.shtml

So now we look towards Eurasian snow advance over the next 8 days for an indication of how the SAI may (or may not) impact this coming winter’s AO. And of course, the SAI update from Dr Cohen in a couple of weeks time. Here’s a crude look at snow advance to the end of the month using the GFS snow depth forecast for the Northern Hemisphere:

 

23rd Oct 1642500453_GFSSnowdepth23Oct2019.thumb.png.1e73423629f4996717eceeb4d8e5d44b.png 31st Oct 1197457000_GFSSnowdepth31Oct2019.thumb.png.dbfc8ce1be7d2a7d6d5b58fa795aee96.png

Edited by Blessed Weather
Final chart should have read 31st Oct.

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so the extent NA snow cover has no impact on the AO what so ever?

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3 hours ago, cheeky_monkey said:

so the extent NA snow cover has no impact on the AO what so ever?

No, snow cover extent is still important. The point was that one indicator (SAI) is better than the other indicator (SCE) as a forecasting tool regarding which way the winter AO mode may lean towards, based on their October results. So para 3 in this paper says:

".....the SAI has significantly outperformed the SCE as a predictor of the winter AO."

However, whilst that may be the case, para 3 of the other paper concludes that snow cover extent was nonetheless important (in 2009/10) for ongoing winter prospects:

"....the record low AO values observed in the winter of 2009–2010 was a result of an unusual occurrence of two troposphere‐stratosphere coupling events that occurred more rapidly than usual and in quick succession during the winter of 2009–2010. ......these two events were forced by a rapid advance in Eurasian SCE and persistently extensive snow cover that supported below normal temperatures and a strengthened Siberian high."

Hope that clarifies your concerns. :oldsmile:

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The one teleconnection not included thus far is the -EPO pattern which is heavily influenced by the SSTA in the North pacific-

This year the SSTs are set back west than the last fee years where the warm water hugs the coast indicating the +VE will be further west.

Pattern wise this suggest the extreme east of the states stays warm with the SE ridge & the deep cold hits the central plains.

Heres the current GFS showing exactly that for day 6 & the EPO trending

A6ED3C43-16BD-4942-BA5A-66E4087B07BC.thumb.png.913dd55fa9e28a0d8704a123227fa77f.png09B43D0C-B0AC-4871-8275-4D24287F9CE8.thumb.jpeg.1209aafdaa3c5269e8e54ea8ebe9af2f.jpeg

- In a nutshell the CORE location being west is good news for the - NAO persistence.. 

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Just to expand on @Steve Murr Steve's post above, here are two diagrams illustrating the positive and negative EPO pattern:

Pos 889560201_EPOdiagpositive.thumb.jpg.ecd4ac2295be414023f500c3ff792e04.jpg Neg 882571810_EPOdiagnegative.thumb.jpg.19584c3c57de6808f124c102a40d5e24.jpg

The diagrams and explanation can be found here: https://blog.weatherops.com/what-is-the-eastern-pacific-oscillation

And looking at this morning's GFS output for 28th Oct provides a great example of the impact of the negative EPO on the northern hemisphere pattern and the downstream implications for the UK. Here's the 500hPa, 500hPa anomaly and 850hPa temperature anomalies (annotated):

1194516941_GFS50028Oct.thumb.png.4d719b8d53bdd8b979dea50c82f762c5.png272695233_GFS500Anom28Oct.thumb.png.027b0f4c7ff81fe5897a89c0be6a6a4a.png1549085497_GFS850tempanom28Oct.thumb.png.712af54b8a58e6224d898e416246aa00.png

 

 

 

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The EPS anomalies have been indicating this very well for a while with the knock on effects downstream. I believe I mentioned it when I used to post in the mod,. thread

ecmwf-namer-z500_anom_5day-2739200.thumb.png.0576a441775c29bfcff6176ec6035618.pngecmwf-namer-t850_anom_5day-2739200.thumb.png.3fab282090f8e28c8f8136e1be5ba6a4.pngecmwf-natl_wide-z500_anom_5day-2739200.thumb.png.2722355644c958c8a54d93cb62393dee.png

Edited by knocker

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No robust evidence of future changes in major stratospheric sudden warmings: a multi-model assessment from CCMI

Quote

Major mid-winter stratospheric sudden warmings (SSWs) are the largest instance of wintertime variability in the Arctic stratosphere. Because SSWs are able to cause significant surface weather anomalies on intra-seasonal timescales, several previous studies have focused on their potential future change, as might be induced by anthropogenic forcings. However, a wide range of results have been reported, from a future increase in the frequency of SSWs to an actual decrease. Several factors might explain these contradictory results, notably the use of different metrics for the identification of SSWs and the impact of large climatological biases in single-model studies. To bring some clarity, we here revisit the question of future SSW changes, using an identical set of metrics applied consistently across 12 different models participating in the Chemistry–Climate Model Initiative. Our analysis reveals that no statistically significant change in the frequency of SSWs will occur over the 21st century, irrespective of the metric used for the identification of the event. Changes in other SSW characteristics – such as their duration, deceleration of the polar night jet, and the tropospheric forcing – are also assessed: again, we find no evidence of future changes over the 21st century.

https://www.atmos-chem-phys.net/18/11277/2018/acp-18-11277-2018.html

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Dr. Butler has observed that one measure that she pays close attention to in winter is the EHF

Poleward eddy heat flux anomalies associated with recent Arctic sea ice loss

Quote

Abstract

Details of the characteristics of upward planetary wave propagation associated with Arctic sea ice loss under present climate conditions are examined using reanalysis data and simulation results. Recent Arctic sea ice loss results in increased stratospheric poleward eddy heat fluxes in the eastern and central Eurasia regions and enhanced upward propagation of planetary‐scale waves in the stratosphere. A linear decomposition scheme reveals that this modulation of the planetary waves arises from coupling of the climatological planetary wavefield with temperature anomalies for the eastern Eurasia region and with meridional wind anomalies for the central Eurasia region. Propagation of stationary Rossby wave packets results in a dynamic link between these temperature and meridional wind anomalies with sea ice loss over the Barents‐Kara Sea. The results provide strong evidence that recent Arctic sea ice loss significantly modulates atmospheric circulation in winter to modify poleward eddy heat fluxes so as to drive stratosphere‐troposphere coupling processes.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL071893

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It might be useful to post this in here now- on the other hand it might not

 

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Below is the latest QBO update from the World Climate Service. Interesting that they believe the delay in the descending eQBO may "undermine" the Saunders et al January and February 2020 winter forecast for the UK (which forecasts a negative NAO and CET 0.5C below the long term average). In a previous post I have already discussed the research suggesting the zonal wind at 20mb may be more relevant to prospects, so I'm keeping an open mind regarding their doubts. You can find the Saunders winter forecast here:
https://discovery.ucl.ac.uk/id/eprint/10080518/1/Saunders_Lea and Smallwood (2019).pdf

World Climate Service:

"The 30mb QBO continues to show reluctance to leave the positive phase: +7.6 for October so far. It's increasingly difficult to envision a significantly negative QBO this winter, which perhaps undermines ideas of QBO-related North Atlantic blocking (e.g. Saunders et al 2019)."

618014905_QBOupdate23Oct2019.thumb.jpg.8e51298740dc0936d26cb79b32bc27bb.jpg

Source: Twitter @WorldClimateSvc

Edited by Blessed Weather

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As the 12s start rolling, with the October update of the Met Office Contingency Planners forecast out today (aka 3 month forecast), I want to share a few (model related!) thoughts about this and how it relates to what the longer range forecast models are saying.  Update is here:

frost-covering-a-sunny-field.jpg
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Bottom line, 5% chance of the coldest quintile (hug it close, coldies!), 50-55% chance of the warmest quintile -  for Nov-Jan.  Not quite the 80% prediction by @CreweCold on the basis of the latest GloSea5 but significant nonetheless.  Note this doesn't cover Feb, the month most likely to benefit from any SSW.  

I was struck though by the reasons given for this forecast, ENSO was dismissed as not a signal either way, two reasons were given:

SSTs in the North Atlantic, specifically increasingly reflecting sub surface temperatures now, I can understand this as the long range models seem to redevelop that cold pool in the Atlantic that has plagued us in recent years.  Not observable yet, but seems plausible entirely. 

This was the second reason, the first was the positive Indian Ocean Dipole - well it is a new one on me!  Researching, the BOM has something to say on it as it clearly impacts Australia:

WWW.BOM.GOV.AU

So what is it (and will I ever get to the point?!), look at the current SST anomalies:

image.thumb.jpg.db66eaca86e6bd13a27f980544a9678a.jpg

It is the contrast between positive anomalies in the W Indian Ocean at the equator and negative anomalies farther east.  

Apparently this increases westerlies into UK, who'd have thunk it?  I can only imagine the mechanism is by messing with the MJO reducing the likelihood of propagation to the  phases that promote northern blocking in winter - that is just a guess, if anyone can confirm or refute, please do!

I have never seen this given a reason for a UK seasonal prediction, have any of you?   What crosses my mind (as someone with expertise in mathematical modelling and uncertainty quantification, but in a totally different area than meteorology) is this:

Do the experts when confronted with seasonal model output that goes against what might be expected, look for reasons to justify what the models are saying, or look for reasons why the models are wrong?  I'll leave that one with you...we will see...

That said, there are plenty of caveats in the CP forecast.

Edited by Mike Poole

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Observed and modeled tropospheric cold anomalies associated with sudden stratospheric warmings

Quote

Abstract Surface weather patterns related to 35 major sudden stratospheric warmings (SSWs) in
1958–2010 are analyzed based on reanalysis data. Similar analyses are conducted with data from seven
stratosphere-resolving Earth system models. The analyses are carried out separately for displacement and
splitting SSWs. On the basis of the observational analysis, it is shown that in northern Eurasia, the cold anomalies
linked to the SSWs tend to be stronger and more widespread before the central date of the SSWs than during
the first 2months after the event central dates. This is particularly true for the displacement events. The cold
anomalies preceding the SSWs are coupled to atmospheric blocking events which trigger the SSWs. While
the role of SSWs as important predictors of cold air outbreaks in the Northern Hemisphere is well recognized,
our results indicate that the impact of the preceding blocking on near-surface temperatures is, in fact, widely
more significant than the downward impact of the SSWs. Thus, stratosphere-troposphere coupling provides
only limited predictability for cold air outbreaks in Eurasia. The models reproduce qualitatively well the typical
large-scale surface weather patterns following the SSWs, but they largely miss the cooling preceding the SSWs
over Europe and western Siberia. Hence, the strongest modeled temperature anomalies related to the SSWs
occur after the events. Moreover, the model results indicate that the tropospheric response to SSWs is stronger
following split events. At the same time, many models simulate too few splitting SSWs.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2015JD023860

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22 hours ago, Mike Poole said:

(SNIPPED)

I was struck though by the reasons given for this forecast, ENSO was dismissed as not a signal either way, two reasons were given:

SSTs in the North Atlantic, specifically increasingly reflecting sub surface temperatures now, I can understand this as the long range models seem to redevelop that cold pool in the Atlantic that has plagued us in recent years.  Not observable yet, but seems plausible entirely. 

This was the second reason, the first was the positive Indian Ocean Dipole - well it is a new one on me!  Researching, the BOM has something to say on it as it clearly impacts Australia:

WWW.BOM.GOV.AU

So what is it (and will I ever get to the point?!), look at the current SST anomalies:

image.thumb.jpg.db66eaca86e6bd13a27f980544a9678a.jpg

It is the contrast between positive anomalies in the W Indian Ocean at the equator and negative anomalies farther east.  

Apparently this increases westerlies into UK, who'd have thunk it?  I can only imagine the mechanism is by messing with the MJO reducing the likelihood of propagation to the  phases that promote northern blocking in winter - that is just a guess, if anyone can confirm or refute, please do!

I have never seen this given a reason for a UK seasonal prediction, have any of you?   What crosses my mind (as someone with expertise in mathematical modelling and uncertainty quantification, but in a totally different area than meteorology) is this:

Do the experts when confronted with seasonal model output that goes against what might be expected, look for reasons to justify what the models are saying, or look for reasons why the models are wrong?  I'll leave that one with you...we will see...

That said, there are plenty of caveats in the CP forecast.

Hi Mike. With regard to your Indian Ocean Dipole (IOD) question.

The short answer appears to be yes, through multiple teleconnection interworking it seems it can impact the UK weather. I’ve got a number of research papers (not yet placed in the Netwx Research library) that provide relevant information about how that happens, but I’ll have to spend some time pulling the pieces of the jigsaw together into a post. Briefly, the IOD has a strong correlation with the Southern Oscillation Index (SOI) which in turn can be used along with ENSO to predict regional rainfall distribution 3 to 6 months in advance.

I’m off for a break in Wales imminently and not back until next Monday, but I’ll see if I can pull more info together for a longer response next week. Meanwhile, here’s two relevant papers linking together what I've just said above:

Influence of the Indian Ocean Dipole on the Southern Oscillation
This finds the IOD “…has a significant correlation with the SOI and the pressure difference index of the tropical Pacific.”
Source: https://www.researchgate.net/publication/229002388_Influence_of_the_Indian_Ocean_Dipole_on_the_Southern_Oscillation

 

Prediction of global rainfall probabilities using phases of the Southern Oscillation Index
“…the Southern Oscillation Index, which provides a quantitative measure of the phase of the ENSO cycle, and future rainfall. The system provides rainfall probability distributions three to six months in advance for regions worldwide….”
Source: https://www.nature.com/articles/384252a0
 

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7 hours ago, Blessed Weather said:

Hi Mike. With regard to your Indian Ocean Dipole (IOD) question.

The short answer appears to be yes, through multiple teleconnection interworking it seems it can impact the UK weather. I’ve got a number of research papers (not yet placed in the Netwx Research library) that provide relevant information about how that happens, but I’ll have to spend some time pulling the pieces of the jigsaw together into a post. Briefly, the IOD has a strong correlation with the Southern Oscillation Index (SOI) which in turn can be used along with ENSO to predict regional rainfall distribution 3 to 6 months in advance.

I’m off for a break in Wales imminently and not back until next Monday, but I’ll see if I can pull more info together for a longer response next week. Meanwhile, here’s two relevant papers linking together what I've just said above:

Influence of the Indian Ocean Dipole on the Southern Oscillation
This finds the IOD “…has a significant correlation with the SOI and the pressure difference index of the tropical Pacific.”
Source: https://www.researchgate.net/publication/229002388_Influence_of_the_Indian_Ocean_Dipole_on_the_Southern_Oscillation

 

Prediction of global rainfall probabilities using phases of the Southern Oscillation Index
“…the Southern Oscillation Index, which provides a quantitative measure of the phase of the ENSO cycle, and future rainfall. The system provides rainfall probability distributions three to six months in advance for regions worldwide….”
Source: https://www.nature.com/articles/384252a0
 

Thanks for the reply, Malcolm, much appreciated and very interesting.  

If the UKMO are citing this as important, I feel the need to understand this mechanism better!   As far as UK impacts are concerned it can't be a direct impact, as the area concerned isn't in any way upstream of us.  So I imagine it must be via changes in the atmospheric angular momentum budget in a similar way to strong ENSO events?  

That does still leave the question, is this IOD driving what will actually happen this winter, or is it driving what is currently showing in the long range models?  Or neither?  Judah Cohen's latest blog is very interesting in terms of what various theories might say vs the long range models...

aer_logo_300x300.png
WWW.AER.COM

October 28, 2019 - Dr. Judah Cohen from Atmospheric and Environmental Research (AER) embarked on an experimental process of regular research, review, and analysis of...

I think this winter might yield some understanding, and, or shoot some sacred cows, we will see, as for me - I can confidently state that I just don't know how it will pan out at all, all of which makes the coming season so fascinating, even if we end up unfortunate and don't get any snow in Wantage!

Edited by Mike Poole

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The latest Seasonal Model updates from ECMWF, UKMO, Meteo-France, CFS, JMA, JAMSTEC, and China BCC have completed and a useful summary can be found on the SevereWeather.EU website here.

Output from 5 of these models continues to suggest a +NAO over the Winter, but I was very interested to see that the BCC model, with possible support from JAMSTEC, are both indicating the high/low pattern will be shifted further east than the traditional set-up typical of +NAO. Also, the BCC forecast strongly suggestive of a continuation of the EPO pattern discussed in an earlier post here. I've annotated the BCC chart below:

BCC 500mb Hgt Anomaly: 1069316039_BCCSeasonalOct2019.thumb.jpg.1dcb7754eda72a72cfba94680ff548bf.jpg

JAMSTEC 2m temps forecast: 841852925_JAMSTECSeasonalOct2019.thumb.jpg.2b35a836baadd023b7b70b2fa57454c7.jpg

Overall the result for the UK seems to suggest a weaker signal for low pressure and strong westerly flow, and an increased chance of colder incursions from a northerly point as a consequence of the continued EPO signal and eastward shifted +NAO with low pressure being situated over eastern Europe.

And although the BCC is out on its own, it does have some basis for its forecast, as I discussed in an earlier post here as the current descending eQBO is possibly down to around 25hPa by now (and the Berlin strat charts available from tomorrow will give a better idea). Here's the relevant bit:

....in a June 2018 paper titled: Surface impacts of the Quasi Biennial Oscillation it was found that:

“…..in early winter (December), responses to the QBO show maximum sensitivity at ∼20 hPa, but are relatively insensitive to the QBO winds below this until late winter. The impact is that Atlantic/European response is shifted eastward compared with the normal +NAO pattern.”

Comments and other thoughts most welcomed.

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Yes. Just got that feeling that this winter is not going to be the status quo +NAO..........

Interesting.

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