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  1. Hi James - yes agreed wrt GWO analysis I also subscribe to the view that the truth is that there is a danger that too much head scratching over a "failed winter" will actually mask the fact the departures have not been as great as believed. The peak period of winter cross section pattern is actually a good fit for highly amplified Nino attractor GWO Phase 6 where the main quasi extra tropical orbit has been focussed. The "missing element" to that height anomaly retro-fit is simply a -ve -NAO - which would have lead on to this as suggested by me back around Christmas in GWO Phase 7 The final third of January came within a hair-breadth of locking in the cold pattern that was trying to establish across the NH to mid latitudes - which the GWO Phase 7 coupled -ve NAM composite advertises. So margins on a macro scale separated only by subtle lack of some upstream split flow into the sub tropical jet flow (typical Nino response) and undercutting of blocking which would have adjusted the Phase 6 composite to show a greater Greenland height anomaly. That instead of the mid latitude Atlantic ridge and too much polar jet flow over the top which proved to the case (a-typical Nino response) But whichever way - a full appreciation of the GSDM diagnostic flags up the +NAM variant among the probabilistic solutions. More philosophical slant on this further down the post. So despite the stubbornness of the NAO reflecting various disparities between tropics/extra tropics and stratospheric domains, the general NH pattern has proved highly meridional as one would expect with a large amount of amplifying +AAM anomalies within the global circulation. Ultimately however they have been manifested within a sub tropical disconnect much more a-typical than one would expect of a high global angular momentum regime. Frictional torque tendency (as a measure of jet stream flow) has, too often, persistently reflected that -ve tendency with recurring easterly -ve wind-flow anomalies at 30N that have been part of the southern Pacific domain in an a-typical Nino (La Nina type) state. In turn, this being the mechanism to force inertia into the poleward jet rather than engage the expected sub tropical Nino flow , and associated more familiar PNA state facilitating greater downstream -NAO tendency, Also very much a season where an SSW in tandem with descending +QBO has also scrambled the usual tropical/extra tropical processes and resulted in usual meridional forcing associated with an +AAM regime being restricted to mid rather than higher latitudes. The above height anomaly cross section depicts the strong amplification within the troposphere - but with disparate MJO/polar domain that negated full engagement of the poleward +AAM planetary wave transport. at higher latitude But in more general perspective and somewhat philosophical terms: This maybe the third time posting, so please accept my apologies for apparent repetition, but the diagnostics are to blame for not meeting (high) winter expectations. Its attempts to try to fit those diagnostics and forecast them into one solution based on human desire to see it verify where the problem lies. If one is prepared to believe that the bias solution is one possible outcome (that can still be reasonably justified) amongst others that might equally verify - then its much more likely that expectations will be met and on that basis no-one should beat themselves (or others) up for it. However, if the diagnostic are narrow focussed to eliminate less palatable solutions, then be prepared to be let down- or, alternatively, be grateful of course if your preferred weather type happens to coincide with a lottery ticket. But don't let the lottery ticket be a fools gold to the usual truth.... and what might happen next time The majority of sources have pointed to increased chances of -AO/-NAO domain this season - whether that be enthusiast, pro met or collective national weather bureau. This increased possibility, using a variety of different (and also interdependent) methods have all come to very similar conclusions - (and on various occasions the numerical modelling has reflected those possibilities too.) On that basis, such analysis, very much including in this thread and other threads on this site, has been a joy to read, of excellent thoughtful and insightful detail and fully justified - and therefore the GSDM diagnostic should not be dismissed based on frustration of an expected favored outcome failing to verify to the extent hoped for/ The key is that a range of probabilities always exists and the best will be gained from these highly useful tools, if the range is always reflected in analysis. This is where weather enthusiasm and science have defined boundaries and while they can overlap and make the pastime/day job all the more worthwhile doing in the first place - there is no room for human preference in the cold science. If it is to be used properly. That applies to each and all of us - even if it contemplating the less appealing outcomes might appear to spoil that enjoyment. So its much less about losing trust, but in contrast much more about keeping trust based on balanced expectations and being prepared for bias to be exposed in the diagnostic processes within the atmosphere and the way the numerical models interpret them Also, the use of teleconnection science is an all year intra-seasonal process - so no need to let one season dominate emotions in that respect either I would look forward to the next season, and then the one after that as a means to move forward and not look back too much. The spaces in between (all the options), if they are allowed to be considered and their existence not denied , leave room for growth and yet more learning - that is the optimum reward in my opinion
  2. I can only really repeat what I have posted previously a couple of times already It is not possible to fit GSDM diagnostics and teleconnections in general into one bias preferred solution (at any time of year and however viable and feasible that solution may be) but especially also try to micro scale squeeze what are intended to be macro scale diagnostics into one very small region within a whole hemisphere the model attempts to represent., Error rate (and disappointment) is bound to increase particularly if all other possible solutions are discounted that the diagnostic might point to. The Global Wind Oscillation calculates changes in velocity and path of wind-flows as transported between the tropics and extra tropics, and represents them via a phase timeline plot. This timeline plot helps the observer identify the progress of momentum transport pattern between the tropics and extra tropics, and between the extra tropics and the polar field. But at this time of year, in the same way as disconnects can occur between the tropics and extra tropics, they also very much can occur between the troposphere and stratosphere when long track upper warming processes within the polar field are on their own very very slow and separate timelines to those within the troposphere. This, at the same time as poleward planetary waves c/o tropical convection activity is propagating through the extra tropics via +MT mechanisms and onwards towards the pole within their own timelines which are not mutually compatible with the downwelling processes within the layers of the stratosphere itself. This has already been covered in depth by @Isothermand others and needs no further comment. But notwithstanding any of that, its clear that the +ve torque mechanisms, and represented high state of relative atmospheric angular momentum in the GWO El Nino attractor phase 6, has already made changes to global wind-flows in terms of the wholesale changes underway c/o the very strong westerly wind additions added to global circulation (and compensating deceleration of AAM at high latitudes) . The term "attractor phase" is used to identify the full capturing of coupling of ocean ENSO base state within the atmospheric circulation that currently has excess westerly winds within the global system . NB The reverse holds true with the La Nina phases where -ve easterly trade winds are being added in the tropics and westerlies added at higher latitudes. In the current Nino pattern circulation, under the laws of conservation of atmospheric angular momentum, the surplus westerlies in the tropics and extra tropics are compensated by increasing (decelerating) easterly -ve momentum at the higher latitudes. This, in tandem with the downwelling SSW -ve wind anomalies means there is a clear retrograding element emerging to the tropospheric pattern with forcing c/o mountain torque replacing the Siberian Low pressure of previously with a Siberian high The watch during the first half of February is to see how far the SH retrogresses and links up with developing cold high pressure pooling over Scandinavia - as the Atlantic pattern starts to run out steam. *See also below related to EPS clusters for brief current suggestions offered that are related to this* So based on arriving at this position, , the GWO cannot have achieved a higher amplitude Phase 6 without poleward momentum transport of +AAM having already occurred. Its more to do in general with high expectations within various site forums and outside winter enthusiasts letting expectations of human bias preference oversee the emotion free dynamics of the atmosphere which operate according to wind-flow propagation timelines. A lot of NWP "model hugging" and a myriad of conflicting solutions present from endless operational and ensemble suites leads many observers down this path of frustration, and to consequently believe that it is the signals that are broken and not the vicissitude of numerical modelling. Everyone can of course be guilty at some time if we take the hemispheric deceleration of momentum into account as described above, then as far as the Atlantic sector is concerned, each breakaway area of vorticity from the fragmenting Canadian split lobe has been like a sprinter leaping off the blocks at high speed and then trying to maintain their speed ploughing into a deep pool of treacle.- as the poleward momentum transport processes evident of recent weeks - finally arrive at the tropopause at the same time as the downwelling processes from the SSW start to carve out upper arctic ridges Taking all the NWP caveats and caution of over-emphasis into consideration, I do nevertheless think that taking a look at the latest EPS height anomaly cluster spilt for the Atlantic and European sector approaching the day 10 period very well advertises an example of where the same processes as discussed above provide separate solutions, with different surface pattern outcomes downstream as to how the pattern may proceed - but both fully supported within the parameters of the GSDM diagnostic. Rather quaintly rustic as these plots are, I think they sufficiently depict that model calculations of the decelerating inertia of the macro scale pattern and appearance of cold ridges is being balanced by fragmenting pieces of ejected vorticity energy from West of Greenland heading into its pool of treacle in the Eastern Atlantic. The model currently shows within two distinct latest clusters a straight split between the energy being dissipated and disrupted under a higher latitude ridge expansion (amidst forward momentum running out of steam) , and the other solution showing enough energy to keep head NE with a less developed (at this stage) higher latitude ridge extension. So with this very latest type of matching outcomes with different surface interpretations in mind, from my own point of view it remains a fascinating but not a frustrating season. My my own weather preferences have increasingly become more and more separate and divorced over time from attempts to objectively learn the processes and try and find the right solution which is not necessarily always the preferred solution. There is always a long way to go with this and much to keep learning, but based on the fact that the GSDM has value intra seasonally, and is not merely a winter cold spell diagnostic assist, I am already looking forward to the coming seasons anyway, and the appreciations they can bring - irrespective of how winter plays out However, even from an attempted neutral stance I think that any "winter only" weather enthusiast waiting for what they would deem real winter weather should not be considering "throwing in the towel". and maybe seeing just how the models handle the next phase of the puzzle before they do so
  3. I think that @Snowy Hibbo has given a good and fair response to parochial interpretations of signals vs models vs outcomes. The post I made last week about the purpose of the Global Synoptic Dynamical Model continues to very much apply as always. I have snipped an extract from the pm thread that @Bring Back 1962-63@Isotherm@Singularity@Snowy Hibbo and myself pitch in and formulate some highly useful collective thoughts on the evolution of the pattern rolling forward and by means of illustrating that we are all the same page in anticipating the pros and cons of the hemispheric view as offered by the GSDM diagnostic. I think this puts in perspective that many of the enthusiasts and professionals are giving full consideration to the range of possibilities within the diagnostics and not just the bias preferred solution. Please bear in mind this section of discussion below was a week back and just as the crescendo of suggestion that evolution to -NAO was imminent and, as at the time, was gaining strong traction between the models. Very much including the EPS. My comments about the "other side" were in reference to an UK component audience elsewhere who were eagerly anticipating the -NAO and HLB as a given - when in fact other solutions, as always remained present. Tamara 308 Replied: January 14 Some different implications exist between the UK and the NE US. The thoughts expressed following Christmas wrt Canadian vortex and downstream pattern have been playing out quite closely in recent days and are arriving now at the point where the continued presence of the Azores high is defying the expectations of the masses in terms of the much touted flip to -AO/-NAO. If I had been still posting on the other side I would have given some analysis of why the Azores high is still there and why the tropical cycle is continuing to support its existence there for the time being. No time to write all that analysis at the moment. I expected something similar to 2012/13 to evolve around the festive period, and it has indeed proceeded about 70% the way there - and is currently stopping just short of it. The GSDM tells the story why.. --------------------------------------------------------------------------- I know that within the pm team others have given their own views about the NAM disconnect and rather than me quote them, I will allow them to provide their own views (if they wish to do so) as supported and agreed by myself, on the conundrums regarding the troposphere and the rather "destructive" aspect this has taken to the sustained reversal of -ve zonal winds in the stratosphere and diffuse response so far The GSDM diagnostic continues to support a very highly amplified pattern, But the diagnostic cannot account for how NWP interprets the signals. The key is to some stubborn a-typical Nino disconnect existing between the tropics and extra tropics that is propping up sub tropical ridging, in tandem with Canadian vortex that would retrogress under a more conducive Nino-like PNA pattern and allow mid latitude amplification to adjust poleward to Iceland and Greenland at the same time as the sub tropical jet stream (rather than the northern polar branch) is engaged by tropical convection imprinting the dateline. This continues to be advertised in the extended period in the same EPS suites that are referred to on this page, albeit there remains some mobility to the pattern rather than a sticking upper ridge. So the scrupulizing of models vs signals continues. But the signals lead the models, the models do not lead the signals. So a good reason to look to the models rather than the diagnostic for their own error rates of the signals when handling disparate stratospheric/tropospheric issues rather than refute the diagnostic itself. As long as minds remain open and not closed only to biased solutions, then the bias solution itself remains possible within the parameters of the diagnostic.
  4. The whole purpose of the Global Synoptic Dynamical Model is diagnostic to numerical model purposes in providing a very useful cross check to performance of NWP with regard to its identification of global wind-flow trends in both the tropics and extra tropics. Changes in inertia of these wind-flows gives a very helpful indicator as to whether jet flow, hemispherically, is increasing or decelerating and whether energy of jet flow is switching poleward or equatorward according to the laws of conservation of angular momentum which alter according to whether easterly or westerly wind inertia is being added to the global atmospheric circulation. Clearly, this helps pin-point when patterns are most likely to amplify in a given part of a hemisphere if one can identify where in the tropics and extra tropics these additions or subtractions of wind-flow are taking place - according to -ve or +ve torque mechanisms that reflect subtractions (jet deceleration) or additions (jet acceleration) of wind-flow. On that basis the GSDM is an intra seasonal diagnostic model which can help spot greatest amplified patterns at any time of year, of which in winter can both help create and augment SSW processes in the stratosphere that lead to increase chances of cold spells. However, like SSW's it is not a guarantee silver bullet to anything - and clearly if the diagnostic process is not used objectively to identify the whole range of solutions that may be present at any given time and simply as a means to try to fit the given signals to a biased preference outcome without considering the other possible outcomes the diagnostic presents - then yes, it will inevitably of course lead to disappointment. Therefore I would respectfully suggest that its not the GSDM diagnostics that "don't work", it can be the human interpretation or assumption of the model that it always leads down a golden path to a desired solution that doesn't always work. Because, that it not its sole purpose. As of the present time, maybe best to try to read between the lines with NWP in terms of the complex array of stratospheric and tropospheric influences and keep using the GSDM to help do this, rather than be disillusioned with it because it appears to be not serving its assumed purpose of fitting the signal to the bias preference Amidst the uncertainty and problems NWP is having with upstream split wind-flows, there are plenty of highly amplified solutions still within model suites this morning - and these reflect and jive with the present diagnostics. Its always a good idea in my opinion not to overly influenced by the vicissitude of numerical models, but to keep checking back on the diagnostics and simply sitting and watching. Kind of being proactive rather than too reactive. Models so often change direction like a swarm of fish in mid stream when they overdo one signal and then cotton on to what is really going on. A whole ensemble suite can be wrong if the model is misreading the diagnostic. Timing clearly also something that cannot be foreseen beyond the best evidence available at any given time The diagnostic always leads to the right solution - sometimes there is also the bonus that is also the preferred one, especially if the reliable signals of poleward rossby wave +AAM momentum transport are identified. These cannot be disputed - at the the very least increasing the chances of tropospheric higher latitude amplification- more so still, with a long -track SSW in town
  5. With the above suggestions in mind, and some 3 weeks passing since espousing thoughts, its time for some more of my own style of analysis The general timing estimates of pattern change from a static mid latitude pattern to one overtaken by stratospheric diminution looks reasonable value on the bigger picture evidence. Within the pm message thread that several of us exchange views, almost a couple of weeks back I focussed on those "provisos" I mentioned in the last full thread summary (as quoted above) that the lull phase of the MJO aka "mini ENSO cycle" would see a fall back in angular momentum tendency and provide a re-set of the pattern ahead of stratospheric diminution. This re-set manifested in terms of some jet retraction amplification upstream that would facilitate momentum within the branch of Canadian vortex and temporary inflation of the Azores high due to associated -ve torque mechanisms in the tropics. The net effect of this to steepen downstream thermal jet gradient adopting negatively tilted trough disruption in the Atlantic sector and falling pressure across the European sector. NWP is now well advertising this anticipated interim passage sequence prior to greater tropospheric/stratospheric coupling of the Northern Annular Mode. I also provided a background comparison to winter 09/10 in terms of the troposphere and the stratosphere displaying a reverse position that has accounted for a restriction to mid latitudes of amplification in the first half of winter 18/9 - rather than elevating further to the higher latitude blocking regime witnessed in the former. It is not the complete story as others such as Tom @Isothermhave covered in great detail and including another very thoughtful post by @Armando Smost recently. However, on the basis that much of the tropical and extra tropical GSDM forcing and associated Global Wind Oscillation behavior has been not too dissimilar to back then within the troposphere, it provides a good illustration of how an unstable lower stratosphere boundary with the troposphere (such as seen in 09/10) is quite capable of producing elevated latitude blocking under similar +AAM conditions and in the absence of, or prior to as was the case back then, of an SSW. I think, somewhat indirectly perhaps, this also helps underpin the disparate points that Tom was attempting to make the other day about the role the SSW and its relationship with the troposphere and how this needs careful interpretative analysis when considering seasonal potential impacts This time around, evolution to an SSW, along slow timelines of maturation downwelling to the stratosphere, is proving to be the catalyst for higher latitude blocking within the troposphere as the next tranch of Pacific forcing comes into view - and such HLB that has been absent due to a stable +ve zonal wind anomaly boundary existing between the troposphere and the reversal at the top of the stratosphere, and which is now finally concluding. So therefore, further to that introduction summary - here are the relevant extracts from my "thinking aloud" post in that informal pm discussion from back then Tamara 278 Replied: January 4 , I continue to think that the optimum time of the Nino tropospheric forcing now underway to "want" to forge a cold higher latitude blocking pattern is being cancelled out by the ultra slow mechanisms within the stratosphere that are stubborn in allowing tropospheric forcing to punch through into the lower stratosphere as I certainly for one was expecting about a week back to see well advertised in modelling day 10 radar by this time As suggested yesterday, its certainly a highly amplified tropospheric pattern with a classical look to the Pacific now (Aleutian Low in strong modelled presence). In this respect compared to, say, 09/10 - the troposphere is arriving at the same state as Dec/Jan - same Nino attractor forcing - "but" the stratospheric profile is completely the other way around to then. The first half of winter 09/10 featured a distinctly cold upper stratosphere but the lower levels were anomalously warm and unstable and highly receptive to the +AAM transport mechanisms and so therefore the amplified tropospheric pattern was highly perturbed within the tropopause layers This time around the unstable, receptive to tropospheric amplification -ve zonal winds are still tucked away too high up to massage the mid latitude pattern to the higher latitude pattern it would be otherwise. Hence why I said yesterday that the Phase 5 GWO composite had (has) the right shape to the textbook composite one - its simply adjusted several hundred miles further south than had been anticipated. This situation in terms of the tropopause will change - the question is will the tropical pattern still be as conducive to supply poleward amplification in the same places. My take is that the risk is increasing, with the delayed disconnect taking longer to complete, that angular momentum may well be falling back just as the downwelling process is becoming more receptive to upper troposphere/lower stratospheric amplification. This might mean that the Pacific starts to re-amplify and "advantage" for SSW effects occurs further upstream than downstream. This might well impact the CONUS with a blast of Canadian arctic air and then a gradient induced effect downstream in terms of seeing a suppressed invigorated jet stream and a cold zonal pattern. * --------------- * (Notice that the concluding paragraph posted some two weeks back, focussed on the evolution to the mid January link to further pattern change as previously discussed in last main thread post. It was not stating the current bridging pattern as any end conclusion) * So therefore what of the way ahead from mid January? I think that the slow evolution of SSW and re-set of the pattern c/o of temporary relaxation of poleward +AAM transport is the bridge that leads to the upcoming renewal of eastward propagating tropical activity to the Pacific which will fairly imminently serve to increase angular momentum tendency once more, retrogress the section of Canadian vortex and the Pacific pattern - and allow the deceleration of zonal winds across the polar field, as stratospheric diminution to take hold. Pressure accordingly rising to fill the inertia vacuum void across the NE Atlantic at the same time as residual trough disruption forms an eastward aspect to the developing-NAO - also concordant with increases the prospects for winter risk across the CONUS as the blocking mechanisms in the NE Atlantic and Iceland/Greenland develop and tend to retrogress with time Such a description fits well enough with evolution of global wind-flows to Nino attractor phases GWO Phases 6/7 c/o +AAM momentum transport in response to tropical convective forcing in the Pacific - and this tropospheric pattern in tandem with tanking -AO profile and representative of a likely destination ahead in the extended period and further into February.
  6. I do not self appoint myself as a "forecaster" but have always tried to stay true to reflecting on my own summary thoughts . I did this on the old site I subsequently no longer participate in - and will continue to do so here Quite happy for my part to accept that the timetable for such complex atmospheric processes as remain in progress is clearly a very moveable feast. But I think in order to stay objective, it is also important when making continuation statement summary updates to retain human perspective of analysis through tacit acknowledgement that the atmosphere is bigger and wiser than all of us - however much we think we are doing our best to advance personal learning curves and hopefully putting something back to help and inform others The general premise of pre-Christmas thinking is/was not wrong in its logical assembly of GSDM diagnostics at the time, but is almost certainly proving too progressive in nature As part of GSDM analysis, I always return to the frictional torque plots to get some idea (in deliberately layperson terms) how the jet stream has been behaving and some idea ahead how it may also affect the tropics and extra tropics based on indicated latest trends. First look at latest updated FT plot (based on usual 2 day lag) Look at circa 30N on the plot and see the further westerly wind bursts (shaded orange) just being added from the tropics and which are creating rossby wave eddies, increasing angular momentum tendency and set to increasingly induce further amplification of the hemispheric pattern as they propagate poleward. With added westerlies now properly switching frictional torque tendency from the tropics, and in the knowledge that frictional torque leads the tendency of mountain torque - we have to take into account propagation times for these processes, with full extra tropical impacts occurring up to 10 to 12 days later. But due to the amount of inherent "westerliness" already present in the atmosphere there is already a next phase of poleward +ve momentum process taking place and recent jet retraction (responsible for stronger sub tropical ridging) is starting in process of reversing. This adds to confidence that the NH pattern *should* only get more and more and amplified at increasingly higher latitudes through January (and discounting possible effects of SSW) Its necessary to factor in the developmental times and associated uncertainties related to stratospheric diminution continuing to slowly unfold. The nature of both the speed and amplitude/eastward progression of tropical convective forcing which is driving future potential tropospheric amplification, and the timing of potential downwelling of -ve zonal wind anomalies have been/are part of the moveable feast I was speaking of earlier. To try to stay as smart and realistic as possible we must keep acknowledging what these diagnostics are telling us Its worth looking once more at the FT plot and looking at when the last +ve momentum transport process took place in November. These are the ones that last drove the Global Wind Oscillation into the Nino attractor phases 5,6 and 7 and ushered in a programme of greater poleward ridging. See plot map just below. (One such from a European perspective being Scandinavian High pressure and a relatively cold easterly for a time and as teleconnected via Phase 5/6 GWO.) if we are to be seeing tropospheric momentum transport and stratospheric diminution come together, then this coupling of troposphere and stratosphere will be reflected by the GWO once again laddering up and orbiting Phases 5,6 and 7 at amplitude. This time around though seasonal wavelengths will be playing Mother Natures part in augmenting the amplification of the tropospheric/stratospheric exchanges and further constructively act upon the SSW - much the gist of the (ebullient) nature of my post just before Christmas. This prospect has not gone away, but we must continue to be mindful of realistic timetables. With this in mind, I tend to agree with @PB GFI on the obs thread that Jan mid month looks to be the earliest time to see the models really switching the decks of the NAM. There are provisos, in my opinion, to this (still likely) scenario - its important that the tropics do not throw any de-amplitude curveballs with convection passage through the Pacific and create conditions for AAM tendency to stall and be reflected in turn within the extra tropics through a lower and less progressive extra tropical GWO orbit Its important that the constructive relationship that the SSW is adopting to MJO amplitude is the one that oversees the more usual MJO progression seen under +ENSO ( and which in itself would constructively act to cement the Nino base state looking further ahead into 2019) To somewhat slant this post further in perspectives : Mid month expectations of real change rather reflects the principle of prognosis of winter 2012 to 2013, if not obviously necessarily precise identical implications for blocking at face value this time around. The frictional torque "starting pistol" was fired properly in late December 2012 ( in tandem with eastward progressing tropical forcing and associated rising angular momentum tendency) . The GWO from mid December 2012 was reflective of suppressed angular momentum (and was due to actually orbit the Nina phases 1,2 and 3 through the festive season). The NH pattern was as a consequence flat, dull and +AO/+NAO zonal into the start of the new year Notice the similarity in November this year in terms of the westerly wind bursts added during November as indicative of the GWO Nino phase orbit through Phases 5,6 and 7 in the next plot. It was this that helped set the scene for January 2013 - in terms of principle comparison we can look to these patterns here in terms of what we know about GSDM diagnostic intra seasonal feedbacks. Indeed AAM reversed from the more distinctly Nina like perspective in December 2012 to reflect +ve momentum transport processes (and extra tropical lag times) to be at almost +2SD GLAAM by mid January - …..no coincidence the time that the NAM flipped and the pattern became much more meridional. This duly impacted the extra tropics from mid Jan (along with an SSW that occurred that month). Blended composite for GWO Nino attractor phases in tandem with SSW came up with something like this for Jan 2013. Close to reality heading into second half of January. The effects of this +AAM/SSW combo had ramifications for blocking further through Feb and the whole of March - which featured anomalously cold conditions in various parts of the NH This December we have some -ve forcing disconnect in terms of the sub tropical mid latitude ridges. I think, by the way, that @donsutherland1posts on another thread about the +ve SOI disconnect and future observations as to how January may play out are highly interesting and played some part in how my mindset has evolved in recent days - and how this particular post has helped come about. With relative angular momentum significantly higher than the same time compared to Dec 12 - the pattern is still inherently more "pre-amplified" (if you will) here in Dec 18, so it provides me with more interest, still, to the way ahead here. With Brewer Dobson circulation c/o temperature differential between the tropical and polar stratospheres at least, if not more buoyant as back then, and with the background Nino pattern a more buoyant atmospheric circulation background to 12/13 (despite the Nina like sub tropical forcing and some emphasis for polar jet flow of this December) then the possibilities for those anticipating and hoping for cold winter weather patterns are obvious, even if nothing in weather can be guaranteed. Likely key difference to 2013 , based on probable forcing, is the propensity for greater retrogression of blocking and probably higher impacts in relation to the CONUS than at that time - notwithstanding any curveballs that might arise. Lets see what happens
  7. So, we approach the turn of another winter month.. and into another year. . ...The atmosphere destined to become supercharged by a combination of constructive action to El Nino c/o the tropical signal in the Pacific, superimposed onto a stratospheric vortex implosion - and seasonal wavelength changes attendant with that new month and new year looking set to pull the trigger on this seasonal cocktail The Global Wind Oscillation, which is a measure of wind-flow inertia in the atmospheric circulation of the tropics and extra tropics, has been coasting in a tight knit very low amplitude Phase 8,0,4,8 for the last week to 10 days. And with the polar field (for now) relatively stable and organised ahead of much discussed developmental changes, this has kept the lid on latent meridional potential of the pattern downstream from the Pacific. Related further to this, current wind-flows depict jet retraction c/o -ve torque mechanisms and some associated polar jet energy assisting the current pre-cursor SSW +AO pattern. Negative zonal wind anomalies as part of this jet retraction illustrated shaded blue on the plot below between 30 and 50N But, so as to rudely interject these processes, another round of westerly wind bursts in the Pacific c/o the propagating tropical signal will build on the inertia harnessed and fluxed poleward during November's positive zonal mean transports - and which has been keeping total angular momentum firmly buoyed ahead of the upcoming shot in the arm to El Nino As the MJO hones in on Pacific engagement - both total and angular momentum tendency are primed to fly as the calendar flips in tandem with these changing seasonal wavelengths - and usher in a high amplitude progression of the GWO into the Nino attractor Phases 5 and possibly 6 within the first 10 days of January Taking into account the widely discussed and anticipated expectations of dramatic changes across the polar field, this phase progression (augmented by those seasonal wavelength changes) teleconnects to a radical switch of the Northern Annular Mode. The festive season mid latitude Branstator ridges, accordingly, migrating to Iceland and Greenland as the stratospheric split engages the troposphere - and with deeper upper cold air advection and increasing surface cold air gathered at mid latitudes, this is a feedback loop for low pressure c/o the southern stream to engage the cold air, as representative of a strongly -ve east based NAO. Progression to GWO Phase 7 (and quite likely Phase 8 as part of a harmonious wind-flow signal with the MJO fully matured in the Eastern Pacific and angular momentum tendency then falling back from its peak) suggests synoptic progression during January might see the blocking regime and associated -NAO signature in the Atlantic retrogress further with troughs making even greater inroads at mid latitudes and continued high impact weather potential as sub tropical air engages the resident cold pools and an awkward wintry mix encounters frozen surfaces. Enjoy your holidays everyone Tams
  8. Tamara

    *** 33andrain -- Happy Anniversary!! ***

    Many thanks for making everyone feel so welcome The site has encouraged a lot of great minds to provide insight and knowledge for members of all different levels of knowledge to learn from. And the respectful and friendly nature of the site encourages and motivates so many more to keep registering - and contribute themselves I obviously highly agree with this and look forward to it further evolving Best wishes to all for Christmas and the New Year Tams
  9. Those that worry that the numerical models are not jiving with the atmosphere should take a look at the VP200 anomaly map forecasts for next couple of weeks. El Nino set to receive a real shot in the arm as constructive forcing and associated agitated rossby wavelength shifts to the Pacific (Indian Ocean suppression) Net result - a surge of westerlies across the Equatorial Pacific (substantive rise in angular momentum) triggering large programming of poleward ridging in the extra tropics - primed to engage timing of expected SSW and associated polar easterly repercussions
  10. This extract...and this next extract... ...are exactly key to the evolution of the pattern looking ahead. The Global Wind Oscillation knocked on the door of Nino attractor phase 5 recently but the extra tropical atmospheric response through poleward +AAM transport did not go the extra mile to deliver a high amplitude orbit through the Nino attractor phases that would synoptically be reflected in numerical modelling by an earlier switch in the Annular Mode. This scenario was actually achieved in December 2009 - and so illustrating that lower level stratospheric disruption through substantive poleward +AAM transport can be enough in itself, (in tandem with a strong Brewer Dobson circulation between tropical>polar stratosphere) to create the type of unstable troposphere/lower stratosphere warm profile that is conducive to high latitude blocking... without an SSW. That was actually to come later in that winter This time around in 2018 a similar pattern of tropical forcing as occurred in late Nov/Dec 2009 looks like being synchronised to provide substantial tropospheric amplification - and at the same time as the polar vortex looks at its most susceptible after we turn the New Year - and augmented yet further by seasonal wavelength changes from December to January which will serve in themselves to help strongly couple the Annular Mode under these conditions. Perming all that together proposes amplitude GWO phases 5 to 7 should dominate a fair proportion of January - and as synoptically interpreted, increase the risk of high impact winter weather scenarios occurring across sections of the NH. Assuming this coming together as reasoned, the blocking would seem likely to be dictated by an elevated +ve AAM state ebbing and flowing these phases - with Phase 7 seeing retrogression of blocking Greenland/Newfoundland and Phases 5/6 closer to Svalbard and Iceland. On that basis a -NAO regime most west based (In relative terms) during GWO Phase 7 and most east based during GWO Phases 5/6 when angular momentum is most peaked and polar easterlies the most robust The takeaway from all this in my opinion is provided that the MJO and extra tropical +EAMT response to it is sufficiently robust, then the deepest SSW is not necessarily always 100% pre-requisite - though that said, taking all background variables into account this season its likely that the need will be greater this time than proved the case in January 2010 - when the strength of the tropospheric perturbance of the pattern into the lower stratosphere was sufficient to sustain a high latitude blocking profile into February when the effects of a later SSW finally came through and kept most of the whole winter very cold.
  11. Hi there - and welcome along I wrote the italicised extract further down this post back in November as part of a private message discussion some us regularly update - with suggestions as to how wind-flow and torque interactions may well play out through the remainder of that month and ahead through December and into January as well. When I (or others) refer to "-ve phase of the cycle", as I have in this extract - its a reference to the tropical convective cycle acting at a certain stage during its typical 30 to 45 day phase progression to work destructively" (or against) the macro ENSO El Nino base state. Negative destructive forcing, within the context of the existing El Nino standing wave, refers to the (temporary) removal of the westerly wind bursts that eastward moving MJO tropical convection cycles typically adds to the atmosphere - and in turn create poleward propagation of rossby wave eddies that serve to amplify jet stream/NWP synoptic pattern over wider areas globally>regionally, the further they head away from their source initiation So part of the process of -ve torques (simply speaking easterly trade wind-flows creating a turning force on the jet stream as they meet westerly winds ahead of/above them) result in the type of jet retraction you refer to in your question. Where this -ve torque occurs in the Equatorial Pacific, then the zonal wind-flow is slowed and the deceleration acts to help buckle and amplify the jet stream . This creates a rise in pressure, with the -ve easterly low level flow underpinning the rise in pressure from within the sub tropics, (but because Mother Nature abhors a vacuum) it forces compensating higher angular momentum adding increased westerly flow downstream at mid to higher latitudes with the effect of adding some extra strength to the polar arm of the jet stream. So effectively the Eurasian jet retraction is a temporary interruption to the poleward amplifying processes at mid and higher latitudes as easterly -ve momentum is added within the tropics and making angular momentum fall there. Here is latest updated MT plot (updated to two day lag). The -ve (easterly/jet retractions) are shown in blue and circled maroon and the opposite +ve (westerly/jet extensions) are shaded orange and circled in lime green (all for added eye-sore clashing pazazz!) Notice the inception points and propagation zones between 30 and 50N The above insight is intended to (hopefully) give some context to my musings below, where I was suggesting an anticipated programme of wind-flow changes, through a timeline of torque process mechanisms - and in turn frame-working the tropospheric/stratospheric evolution and higher latitude blocking potential discussed within these pages as we (now) arrive close to the festive period Tamara 181 Replied: November 21 I hinted at a -ve phase of the cycle heading into December the other day. In some of the recent years this has been a test of the default pattern, and a period of -ve AAM tropical momentum forcing has applied some +ve AAM energy into the polar jet that has lasted a few weeks and allowed some polar vortex consolidation. This year however, as we all know, so many variables are aligning to keep the polar field weak and unstable and also crucially look like teleconnecting to keep tropical convection active, and therefore prevent AAM momentum in the tropics falling too far and for too long. The signs at the moment in my opinion are that a repeat sort of sequence of recent weeks may occur - the difference being that seasonal wavelength changes will augment a very harmonious tropical and extra tropical wind-flow signal in Phase 8 producing, initially, a robust torque inversion and retraction of the Pacific jet - then followed by a further programme of strong forward +ve poleward momentum as the MJO re-tracks through the I/0 This, quite likely, taking usual GSDM lag-times into account - has quite large stratospheric implications for the latter half of December and maybe especially into January and perhaps the *bigger* cold air advection ambush version of mid/late November. The unstable GWO orbit profiles of Phases 5,6,7,8,0,4,5 etc I was describing last week as a possibility this winter - are hinting at unfolding and this suggests a high impact weather scenario risk across the NH. . This unstable type of Nino GWO profile actually accentuates the intensity of pattern switches because the default +AAM momentum anomaly of an El Nino features brief, but quite vigorous punctuations of loss of momentum each time the tropical signal passes Phase 8 into the Western Hemisphere. With background global wind-flows countervailing the extent that these pauses can assert themselves, and awash with westerly inertia, the brief decelerations of +ve AAM momentum in the tropics simply act to re-set the long-wave pattern in the mid and higher latitudes with -ve momentum subsequently transferring back at higher latitudes as the tropical cycle heads back through the I/0 to the Pacific. And so on and so forth. If all the extra tropical jet stream energy remained 100% of time focussed in the southern stream then ultimately blocking patterns actually start to break down. But sudden subtle switches of a little momentum back polewards re-distributes and provides re-set of the pattern by diverting some energy back across the pole, further acting to destabilise the AO. As a consequence, this creating simultaneous re-distribution and re-grouping of upper cold pools poised to be advected back to mid latitudes when the dominant poleward +ve AAM cycle soon resumes ...and polar easterlies strengthen further In short, a little -ve momentum within a dominant +ve Nino default atmospheric cycle is actually an ideal thing to see (for those who are looking for substantively cold winter patterns). So yes, from an objective neutral GSDM point of view, its highly interesting to see how this evolves and plays out. …………………………………………………………………………………………………………. I think that the Global Synoptic Dynamical Model (GSDM) (which is a diagnostic model concept to NWP performance in terms of how the numerical models interpret global wind-flow changes as manifested through the jet stream) is following quite well the suggested script (and contained explanations and reasonings therein) as given above All highly pertinent, but maybe especially the bolded sections. The aim of this analysis is not to try to give complete monthly or seasonal forecasts per se - the GSDM is simply a highly useful diagnostic framework to build on and see how all the relevant drivers in play seasonally and inter-seasonally may interact accordingly to provide the bigger picture that professional and amateur mets use to put together a macro assessment I believe this framework very nicely fits those savvy macro assessments such as the andrain "influential" experts provide on these latest pages So, by way of conclusion, it looks like a quite rarified NH profile may evolve, with retrogressing and re-setting higher latitude blocks in tandem with an activating -NAO domain - heading from 2018 into 2019 that has quite a few similarities to the change-over of 2009 into 2010 in terms of poleward +AAM anomaly transport peaking at a time when the stratosphere looks to be its most unstably split this winter. So -ve torque. polar jet phase of disconnect (jet retraction) is best seen as a re-set of the NH pattern before potentially high impact wintry weather events assail regions of the US and the other side of the Atlantic
  12. Hello Tom - yes exactly The deep convective signal moving through the I/O is allied to highly conducive conditions for convection in the Western Pacific to generate further significant westerly momentum - set to propagate across the tropics into the sub tropics. Without forgetting also, the net westerly inertia still in the atmospheric circulatory system as produced during November, both total and relative angular momentum tendency will rise once more and sharply terminate the latest -ve disconnect. GWO (subject to two day lag) in high amplitude Phase 8 (as anticipated some 10 days back) - is reflective of current -ve atmospheric tendency to the base state and in simple terms relative to the present position amounts to *some* scrubbing of surfeit westerly inertia within the global atmospheric circulation. The tight re-coupling of the atmosphere/ocean to the Nino standing wave that follows this disconnect period looks set to usher the Global Wind Oscillation back to high amplitude Phase 5. and in agreement with the timelines that Tom suggests Torque mechanisms should subsequently focus the GWO in the El Nino attractor phases 5 ,6 and 7 during January which synoptically mirrors a robust -ve NAO signature and +ve height anomalies from Newfoundland to Iceland. This, underpinned by the likely stratospheric impacts to conclude the year The significance of the shorter term -ve tendency to El Nino is setting up the scenario where the polar vortex looks like a large structure that flatters to deceive and is in reality set on weak foundations, so that low heights will readily disrupt to mid latitudes and set the scene for potential high impact weather conditions as the AO increasingly slides into -ve territory and cold air advection descends from the higher latitudes. Furthermore, perming the GWO in significantly elevated angular momentum quasi-stationary orbit alongside a distressed polar field - then crucially, seasonal wavelength changes from December into January will further augment the substantively amplified character of the NH, and could lead to some quite noteworthy wintry conditions both side of the Atlantic into the New Year. GWO Phase 5/6 correlating to Icelandic blocking retrogressing towards Greenland/Newfoundland in Phase 7 and a multi standard deviation -ve coupling of the Annular Mode. @Snowy Hibbo Please see my pm message for correct representation of my post Just to add in reference to the above analysis - updated frictional torque plot reflecting the eastward progression of tropical forcing in I/O and acting as lead for forthcoming tendency of MT within the extra tropics. A solid signal that -ve tendency to El Nino has found its floor, and angular momentum tendency to start rising once more in the coming days to re-claim the surfeit of +ve AAM (westerly) wind-flow within the atmospheric circulation. This fully supports a GWO orbit through Phases 8, 0 and 4 and then engaging that +EAMT response (Pacific jet extension)back into Nino attractor Phase 5
  13. This is an excellent response explanation to help define the tropical and extra tropical interactions at present,and moving forward. We know that the precise relationship that the atmosphere adopts to the ocean base state is not always linear within any ENSO event. In this way, its quite possible as is the case now, for the atmosphere to show an aggregate elevated surplus of westerly wind inertia "constructively" acting over and above the already +ve ENSO base state. This, just as much as -ve disconnects to the cycle can occur, f.e when the MJO acts "destructively" to the base state at the end of an intra-seasonal cycle - with the effect of scrubbing out some of the excess westerly wind inertia within an already +ve ENSO base state The converse holds true - as last winter illustrated when La Nina was destructively acted on by the strongly +ve momentum cycle c/o high amplitude eastward moving MJO wave, with the result that the Nina standing wave was temporarily reversed at the time of the SSW. That case study illustrated the east based nature of the La Nina event, prior to its dissolution during the Spring, where convergence zone tropical convection increasingly occurred much further east than during a typical La Nina. As one of my previous posts discussed. With all this in mind, one of the vital assets of the Global Synoptic Dynamical Model is that it enables us to apply a diagnostic approach to global wind-flow evolutions within the tropics and extra tropics and make balanced judgements as to how propagation, amplitude, acceleration (westerly inertia) and deceleration (easterly inertia) of wind-flows, impacts the dynamics of the relationship between the troposphere and stratosphere as a whole. This very important diagnostic element helps us check the accuracy of how well the numerical models are reflecting these changes in wind-flows - and as a consequence also the accuracy of the synoptic patterns represented by them as well Such accuracy can be checked by taking into account the lag-time periods of torques impacting through AAM tendency>GLAAM, as part of the GSDM diagnostic, and that @Isotherm astutely refers to. It is the inflexion point of where wind-flows create... * Convergence (precipitation) manifested as westerly / +ve torque mechanisms and/or * Divergence (stable suppression of convection) manifested as easterly / -ve torque mechanisms …...that alters the turning force of the Jetstream and induce +ve or -ve frictional torque responses, and associated, +ve or -ve switches in angular momentum tendency according to which wind-flow is ascendant at that time. These wind-flow anomalies propagate to the extra tropics according to circa 10 day lag times and impact the extra tropics This overview of torque/ AAM tendency interplay then can be broken down further by considering how "stable" the GSDM angular momentum budget of global-wind-flows is (meaning the overall net westerly inertia vs easterly inertia in the atmosphere) set against the ENSO state in terms of its spatial distribution of temperature anomalies that dictate within that ENSO regime. The AAM budget of wind-flows, in its state of constant flux, alters continually according to the changing inflexion points of where opposite wind-flows meet within the tropics and extra tropics. The relative stability, or, instability of the AAM budget determines where, and to what intensity, convergence of wind-flows is most likely to occur - and in turn be most highly likely to cyclically induce MJO thunderstorm development and focus associated westerly wind bursts. These westerly wind bursts promote further inflexion points and subsequent convergence zones and associated active tropical convection - and also therefore, as a consequence, keep the processes of upwelling of sub water and re-distribution of spatial SST anomalies within the ENSO zone progressing forward, as part of the natural evolution of the major ENSO cycle. So, to apply a lot of the theory into the practice: The identification of the most spiked zone of likely convergence zone of Pacific/West Pacific SST's surrounding the ENSO zone that @Isotherm correctly points to - provide the focus point for the most +ve AAM tendency anomaly feedback as part of the most intense coupled forcing within the "mini ENSO cycle (MJO/GWO) vs the lull phase of that mini cycle - which is identified as the tropical signal passes from the active El Nino Pacific Phases - on into the Western Hemisphere. The Western Hemisphere represents where the greatest -ve tendency set against the +ve GLAAM state is to be found - and therefore where the GSDM budget of wind-flow inertia is at its most "unstable". set against the ENSO base state This unstable GSDM phase of the mini cycle determines the extent of (temporary) disconnect of the atmospheric response to the base ENSO state. Now, how do we transfer all these complex interacting dynamics onto a suitable pro-forma to bring it all together? The Global Wind Oscillation (GWO) is a plot depiction of the total wind-flow aggregate within both the tropics and extra tropics. I have "borrowed" *she adds tactfully* a link to a quite recent GWO orbit update posted on another site( probably from a subscription paid site), as unfortunately free locum access is still currently not possible to the GWO/FNL plots (that updates daily subject to 2 days lag) So, that update to the 25 November shows the GWO in El Nino high amplitude Phase 6/7 - reflecting the very high +ve GLAAM state relative to the Nino standing wave base state. Note the extensive propagation of +AAM anomalies c/o orange shading, with time, from the tropics to the extra tropics As stated and indicative of forecast above, the tropical cycle is now set to return to the Western Hemisphere ahead of next eastward progression through the I/O. Excess propagated poleward +AAM anomalies in the global atmospheric circulation promote a -ve frictional torque in the tropics, thereby adding -ve easterly wind anomalies to compensate for the significant westerly wind inertia created by the El Nino standing wave feedback in the Pacific. This natural compensation of wind-flows reflecting Mother Nature's abhorring of a vacuum. On the frictional torque plot below, note the inflexion point of -ve tendency wind-flow at 30N as per the blue shaded anomaly. At the same time note the existing +AAM anomaly depictive of the westerly wind bursts persisting above these at 50N Such a vacuum, as described, is therefore shown to be calculated as -2SD negative FT tendency set against a peak of +3SD GLAAM. An inherently unstable -ve tendency disconnect of the AAM budget is imminent - as AAM tendency subsequently falls back in conjunction with the tropical signal entering the Western Hemisphere. Due to 2 day lag of data-sets, this is yet to fully show on relative AAM tendency plots The GWO will be reflecting this programme of wind-flow sequences through a rapid orbit to Phase 8 (scrubbing of westerly wind inertia and adding of easterlies). However, the subsequent continuation of the MJO through the I/O looking set to re-balance the unstable GSDM profile through rising +frictional torque and AAM tendency - and so returning the GWO right back to the Nino attractor Phase 5. This adds back an additional surfeit of Nino westerlies and resumes further poleward +AAM anomalies and the constructive co-operative action of the atmosphere with El Nino. It also has implications for re-setting the NH synoptic pattern to that seen around the second and third week of November - but, because we know that frictional torque tendency leads lagging mountain torque tendency, the greater of those implications are for the stratosphere looking ahead from the festive period and most especially perhaps into the New Year time.
  14. The importance of the two links above focus on high latitude blocking responses related to ENSO phase - but one must closely observe a requirement to differentiate between higher latitude and mid latitude blocking when considering extra tropical responses to convectional forcing in the tropics. The relationship is quite different to that observed in the paper if mid latitude blocking is more likely than higher latitude blocking. The MJO is an intra-seasonal phenomena of variability and therefore is pertinent to all seasons of the year, and not merely a stand-alone influence on winter patterns. The presence of higher latitude blocking responses during winter, most especially, assumes that all inter-connected variables present beyond that of merely considering the MJO (ozone distribution c/o BDC circulation, sea ice patterns, solar forcing etc) are conducive to an unstable stratospheric profile that either assists a disconnected relationship between the troposphere and the stratosphere and/or a relationship that is favorable to top-down destabilising influence of the stratosphere to influence the troposphere. If the background variables present in such a given season do not pre-dispose to either type of weak relationship within the polar field, but point instead towards a stable and organized (cold) polar vortex, then the MJO responses under consideration apply quite differently in relationship to blocking patterns, found at mid latitudes to those discussed by this paper focussing on higher latitudes. With this in mind, under a +AO regime, Atlantic and Pacific blocking (mid latitude) is conspicuously absent at many times of the year, including the deeper part of winter according to seasonal wavelength changes, when teleconnected with an El Nino regime. An El Nino regime promotes a dominant Pacific jet extension and a cyclonic Pacific and downstream Atlantic profile. The downstream ridge response to this wavelength switches ridging from the Atlantic into Europe - assuming the polar westerlies are too strong to allow such a block to migrate northwards. However, and conversely, Pacific/Atlantic blocking is a signature response to a traditional La Nina phase where easterly trade winds are ascendant and so therefore serve to amplify High pressure in the Pacific with a downstream longwave pattern which teleconnects to disturbances pushed eastwards into the US (commonly engaging the tornado alley season in Spring for example) and a further downstream sub tropical ridge response over Bermuda and intensification of the Azores High. The relationships are further complicated however by the various spatial SST convergence zones that can set up within the ENSO zones and determine where organization of MJO thunderstorm development is most active. This has significant effects on the MJO patterns as distinct from traditional events, and in turn can produce a-typical blocking responses. An east based La Nina, as seen last winter for example, often produces an a-typical El Nino response due to the West and Central Pacific seeing anomalously warmer water than under a traditional La Nina, and so therefore also significantly warmer than the colder than average eastern most ENSO zone . This spatial SST regime accentuates the chances of a tropospheric/stratospheric pathway being enabled due to MJO patterns converging further east than under a typical La Nina - and so therefore greater poleward propagation of +AAM anomalies which alter the typically dominant amplified Pacific and Atlantic patterns to one that more closely resembles an El Nino (+ve EAMT jet extension and potential stratospheric disruption). This also therefore increases the chances that such a La Nina pattern may, a-typically, produce a high latitude Nino type pattern as identified by the paper, should such substantive stratospheric disruption occur. This, equating to the Phase 7 type MJO evolution as discussed by the paper. The converse holds true with an especially west based El Nino, where tropical convection patterns are accordingly also found further west of the dateline than under a typical El Nino, and this may produce a more disconnected extra tropical (GWO) pattern characteristic of relatively lower angular momentum regimes and hence both Pacific and Atlantic regimes more amplified, overall, than found under a traditional regime. This in turn affects the tropospheric/stratospheric relationship and potential for higher latitude blocking - where the strongest forcing is further away from the Eastern Hemisphere and so rossby wave propagation is also less likely to have influence on amplifying higher latitudes in these regions of the NH. The "summary and discussion" extract of the paper does suggest that these studies are based on sample sizes and further investigation is compelled. This re-enforces some of the present discussion in that there is no linear x+y=z El Nino/La Nina relationship to the MJO and blocking that exists. It is dependant on the precise relationship that the atmosphere adopts to the ocean base - and where the principle forcing within any given ENSO state regime exists. This in turn affects, when considered alongside all other interdependent variables, the precise state of the Annular Mode in that given season.
  15. Some latest model forecast suggestions of -ve angular momentum tendency "destructively" working against the Nino base state. However, one must question just how "destructive" this might be. These forecasts of course are linked to the passage of the MJO into the Western Hemisphere and attempting to re-amplify the Pacific a little - as *some* of the dominant westerly wind inertia now fully engaging the atmospheric circulation c/o the Nino base state is, just for a time, scrubbed out. Ten day ensemble means within the numerical models are now fully advertising this sequence. It is vital though that the angular momentum forecasts, as posted above, are seen purely as predictions of interim tendency of AAM falling set against a GLAAM state that is now emphatically into Nino territory during the latest +ve momentum transport stage of the tropical/extra tropical "mini ENSO cycle" One must question how far GLAAM will fall (in relative terms) during the upcoming lull in tropical forcing before it rises potentially more strongly than seen during November. In some of the more recent cold-biased early stage winters such as 2012/13, a period of -ve AAM tropical momentum forcing has applied some compensatory +ve AAM energy into the polar jet that has lasted a few weeks and allowed some polar vortex consolidation - that is, relative to a weak seasonal vortex These La Nina type destructive disconnects are appearing more frequently within El Nino regimes for background warming linked reasons - and which are of high significant interest for sure, but belong probably to another thread discussion. This year however, as most of us know, so many variables are viewed and supported with intuitive reasoning to be aligning to keep the polar field weak and unstable. Therefore they also crucially look like teleconnecting to keep tropical convection active, and so prevent AAM momentum in the tropics falling too far and for too long to allow the polar field to re-group and allow the Annular Mode to teleconnect towards keeping more cold air bottled up within the arctic. So I believe the upcoming spell of (relatively) greater polar jet energy switch needs to be looked at within this perspective. The signs are that a repeat sort of synoptic sequence of recent weeks may occur - the difference being that seasonal wavelength changes will augment a very harmonious tropical and extra tropical wind-flow signal (MJO/GWO) through Phase 8 producing, initially, the torque inversion and retraction of the Pacific jet that adjustS some jet stream energy poleward out of the Nino based southern stream as already implied - but then followed by a further programme of strong forward +ve poleward momentum as the MJO re-tracks through the I/0. This suggests that the re-bound Nino-kick to the atmosphere could be the one that sets up a moderate Nino ocean/atmosphere coupled relationship for the rest of the season, that, taking usual GSDM tropical>.extra tropical lag-times into account acting on an already weakened seasonal polar vortex - has quite large stratospheric implications for the latter half of December and maybe especially into January and *perhaps* the biggest cold air advection ambush of the season. An unstable type of Nino Global Wind Oscillation profile is implied by this Pacific/Western Hemisphere/I/O type of progression that potentially serves to accentuate the intensity of pattern switches because the default +AAM momentum anomaly of an El Nino features brief, but quite vigorous punctuations of loss of momentum each time the tropical signal passes Phase 8 and into the Western Hemisphere. With background global wind-flows awash with westerly inertia and spot welded within a Nino state (countervailing the extent that these La Nina-esque lull phases of the "mini ENSO cycle" can assert themselves) the brief decelerations of +ve AAM momentum in the tropics simply act to re-set the long-wave pattern in the mid and higher latitudes with -ve momentum subsequently transferring back at higher latitudes as the tropical cycle heads back through the I/0 to the Pacific. And, in theory, so on and so forth as long as the background variables continue to support a disconnected tropospheric/stratospheric state that doesn't allow upper polar westerlies to top-downwards. If all the extra tropical jet stream energy remained 100% of time focussed in the southern stream then ultimately blocking patterns actually start to break down. But sudden subtle switches of a little momentum back polewards re-distributes and provides re-set of the pattern by diverting some energy back across the pole, further acting to destabilise the AO. As a consequence, the creating of simultaneous re-distribution and re-grouping of upper cold pools that are poised to be advected back to mid latitudes when the dominant poleward +ve AAM cycle soon resumes ...and polar easterlies strengthen further In short, a little -ve momentum within a dominant +ve Nino default atmospheric cycle is actually an ideal thing to see (for those who are looking for substantively cold winter patterns). This, re-enforcing the perspective as offered in relation to angular momentum tendency forecasts. These provide an excellent parallel to the snapshot in time direction of the tropical>extra tropical cycle, but they are not a face value interpretation of the major ENSO cycle related to how a consolidated El Nino circulation will impact global wind-flows - and which looks set to control the months ahead. The break-down point of cyclical cold air advection patterns from high to mid latitudes will come if and when the tropospheric/stratospheric disconnect becomes unsustainable due to breakdown on Brewer Dobson circulation and concentration of ozone within the polar field, and linked with the westerly QBO transition, is too far advanced to hold the polar westerlies within the upper atmosphere. This would threaten a very messy and "episodic" latter part of winter as sub tropical air attempts to overwhelm entrenched cold pooling at the mid-higher latitudes in various parts of the Northern Hemisphere. Objectively, and despite constructing this post and looking at the bigger picture from a neutral and non-cold bias point of view however, any sustained breakdown beyond some comparatively shorter milder spells, seems unlikely for the first part of winter at least.. Edited: Just to add, whilst deterministic MJO models are not wholly reliable beyond about 5 days, they tend to underestimate tropical forcing, especially taking into account the active patterning that is favored, and as discussed in this post. So it is significant that the ECM is stepping up both the speed and amplitude progression of the Phase 8/1 orbit onwards and eastwards through the Indian Ocean. Very much mirroring the November imprint progression. The implication of this is to fast track renewed tranches of robust poleward amplification leading to a rinse and repeat of the present pattern and that stratospheric implication as previously mentioned - as rossby wave dispersion engages large +ve EAMT forcing as it heads poleward..