Jump to content

Tamara

Members
  • Content count

    2,851
  • Joined

  • Last visited

  • Days Won

    27

Tamara last won the day on February 10 2017

Tamara had the most liked content!

Community Reputation

16,648 Exceptional

Profile Information

  • Gender
    Female
  • Location
    Hastings

Recent Profile Visitors

59,445 profile views
  1. I quite often agree with your sort of sentiment, as I'm one who opts to look at the most likely solution to fit the signals rather than the preferred one But, equally impartially and with intended objectivity (hopefully): The situation at present is a highly unusual one and the risk of some astonishing late season wintry weather is much higher than usual, certainly than often seen in these cases where deep cold pool advection flirting with the UK graces the perimeters of more 'reliable' NWP The repercussions of this SSW are going to be sustained. The clock starting ticking back in January and carried on through this month with extreme instability of the atmospheric profile with the tropics and extra tropics being subjected to opposing high amplitude states of angular momentum tendency. The impact on tropospheric global wind-flows (the Jetstream) has been significant, in addition to the detonation of some intense cold pooling over the polar field (relative to the modern day generally warmer arctic) : more especially across the Canadian arctic as multiple programmes of hot needles are probed into the polar stratosphere The result of extreme tropical momentum and stratospheric implosion implies high impact weather events on a broad-scale. Some places are going to get bitterly cold and some weirdly warm. In this day and age fewer parts of a hemisphere can get cold with less to go around than used to be the case maybe. But this programme of events strongly favours the European sector to become bitterly cold from what looks to be an impressively large breakaway cold pool for the time of year from Siberia. While its true that the envelope of this cold has boundaries that shift in intra suite modelling, the focus of the BI being impacted in inclusion, is much higher than other situations where lesser broad-scale drivers have been in evidence Ramping indeed requires a justification - I think this situation fits that criteria. Areas of land mass infrastructure most at risk aside from weather impacts (hopefully with least human welfare risk), the synoptic blocking pattern and its associated reverse polarity from one side of the Northern Hemisphere to the other - is not something seen on an every day NWP menu
  2. Posted February 10 Irrespective of what the ECM goes on to show shortly and irrespective of what my head keeps telling me of how the effects of this SSW could be mitigated, I am not sure I have seen anything programmed quite like this thing. Polar easterly reversals are often enough mitigated at least to some degree by other tropospheric drivers, but I am beginning to come to round to thinking this may not be one of them where that happens so easily and its going to take over a lot of the NH for some time. it could be the case that it would start to be more prudent not to underplay the SSW, than place caveats as to what might mitigate it. On that basis maybe its me who should have a bit of a ramp, and not others who should restrain themselves However it plays out in terms of what comes out of the sky in the coming weeks - and despite the fact that the actual phenomena of SSW's is not new, this is quite a significant specimen indeed we are watching unfold ............................................................................ A week on, and a crazy amount of pages later, what has changed? Well I haven't had another ramp, and the deepest cold is still 9/10 days away But what has become clear in the course of a week is that the first stratospheric break-down salvo is set to verify for certain this week - and that day 9/10 day period marks Phase 2 and the time when the Canadian vortex to the NW should finally back off and the down-welling process of -ve zonal wind anomalies really start to make themselves felt in out part of the Northern Hemisphere On that basis we can give credence to the shape of the mid and higher latitude pattern and emerging block alignment with the deep cold backed up like a dam waiting to be unleashed I am amongst the most sceptical of day 10 UK deep cold in NWP and very often based on the realistic signals, barely take a second glance, if even much of a first glance at all But this SSW is a significant specimen indeed, and no further deep analysis is needed. On that basis I will be taking this particular day 10 deeper cold rathe more seriously as a contender The fact that Phase 2 marks the time when the strongest sibling vortex lobe starts to finally cave in after its winter rule, increases the chances of deeper cold air advection at that time-period not just because the block to the NE can start to orientate in ideal position as polar jet energy is finally being squeezed out, but because the chances of retrogression are also much higher so that at some stage re-loading deep cold has a heightened chance of finding out even this little Island. Probably the most simplified basic principle post you will get from me - but less is more sometimes and nothing else needs to be added
  3. You are quite right As was Captain Shortwave observation at the same time about the amplification in the Pacific sector. And that remains the clue, despite suspending usual thought yesterday for good reason. We can all think we are missing something when there are extraordinary things happening at all levels of the atmosphere. But seeing as I have returned to my head attempting to be in control over what is happening, then as previously suspected - its the case that falling angular momentum since the MJO induced Scandinavian ridge of last week, is meaning that -ve zonal easterly winds are lining up again from along the tropics at 30N As repeated a bit like a stuck record by me this season (sorry about that but its based on intended good reasoning) the effect of a return to more La Nina-like type forcing (for the time-being)is to re-boot the sub tropical ridges aligning along 30N. The classic configuration of this forcing this winter has built up the signature traditional default pattern of amplified North Pacific ridge which locks in the Canadian vortex, with increased polar jet energy and further sub tropical ridging downstream pushed to mid latitudes across Bermuda and to the Azores ridge. The -ve zonal wind anomalies supporting these ridges underneath, with the polar jet flow across the top. Very much a +NAO regime. However much members dislike it, that is what the ECM operational keeps modelling each time at the moment into the medium term, and its not hard to see where it is coming from - based on its interpretation of the recent very high amplitude tropical forcing concluding its cycle - and with those -ve zonal winds returning across the 30N as angular momentum falls back ...ahead of the next tropical cycle retuning to the Indian Ocean. If one thinks that the deep amplitude low angular momentum GWO pattern of January helped cement the Canadian vortex at a time when the polar field is typically at its most organised, then as suggested in posts at various times through January (and in anticipation of the latest MJO forcing) it was always going to be a big ask (initially) to change an entrenched tropospheric base state pattern - which in turn frameworks the polar field. I think a weak El Nino forcing, in tandem with eQBO would have created the stratospheric pathway that does not favour amplification restricted upstream in the Pacific and does not teleconnect to a strong Canadian vortex lasting in latter winter and being more resistant to any poleward wave flux that does come from phases of tropical momentum Under a feedback pattern that produces steady background poleward +AAM forcing, and unlike a La Nina regime not relying wholly on tropical convection forcing to boost westerly winds in the tropics as a means to amplifying the extra tropics downstream (the Atlantic and European sector) then this SSW would have taken route 1 - as last weeks +AAM spike produced in terms of the Scandinavian ridge and less upstream energy waiting to return c/o the Canadian vortex. .The SSW would be more likely dealing in those circumstances with a sibling Canadian vortex and parental Siberian lobe - rather than the other way around as we see at the moment, and as very well described by @lorenzo on the stratosphere thread today Its a case in my opinion of the tropical cycle re-setting from the Indian Ocean and angular momentum rising once again. Also I think that March will see the Pacific profile change and warmer sub waters changing to mean that a more sustained +AAM cycle will evolve as a signal that this La Nina is going to fade though the Spring into early summer. So an extension of 'winter' and a cold March does look intuitive on that basis at this stage Before then, however and notwithstanding all said in intended sense as above - its still very much the case to watch this bag of tricks called the SSW . As soon as the parent Canadian vortex shows weakening and the models factor in better the constantly new starting conditions based on the Krakatoa evolving from the highest levels of the atmosphere downwards, then the stubborn tropospheric pattern c/o (weakening) low angular momentum forcing should become less dominant and more easily overridden - especially as wavelengths shorten and assist cold air advection heading into March
  4. Irrespective of what the ECM goes on to show shortly and irrespective of what my head keeps telling me of how the effects of this SSW could be mitigated, I am not sure I have seen anything programmed quite like this thing. Polar easterly reversals are often enough mitigated at least to some degree by other tropospheric drivers, but I am beginning to come to round to thinking this may not be one of them where that happens so easily and its going to take over a lot of the NH for some time. Its one of those very occasional cases in point where referring to the direction of travel of the GSDM is certainly not the whole story when it comes to tropospheric forcing and the placement of the jet stream, set against such a considerable reversal of zonal wind anomalies coming into the troposphere. So on that basis, putting aside what my head has been telling me, it could be the case that it would start to be more prudent not to underplay the SSW, than place caveats as to what might mitigate it. On that basis maybe its me who should have a bit of a ramp, and not others who should restrain themselves However it plays out in terms of what comes out of the sky in the coming weeks - and despite the fact that the actual phenomena of SSW's is not new, this is quite a significant specimen indeed we are watching unfold
  5. The decent orbit was the GWO 5-6-7 part. It changed the upstream profile and enabled the door to be shut on the Atlantic that has been fed for so long by the low angular momentum combination of increased polar jet c/o Canadian vortex and bumped up sub tropical ridges due to enhanced easterly trade winds. Its proved brief - a jab around the edges as I described it might be about 10 days back. The heading to GWO Phase 8 part has curtailed the Scandinavian ridge and returned greater polar flow with angular momentum falling back once more as the vigorous tropical momentum phase c/o MJO comes to a conclusion as it arrives at final high latitude destination. The fall back in AAM now entails looking at the 'back door' Atlantic ridge route to height rises over the arctic c/o the SSW. We have seen plenty of these scenarios many time before. The height rises across the arctic are not in question. Self evidently as I said yesterday the highly impressive reversal of zonal winds will effect the higher latitudes into the troposphere through a quick response. But as other SSW events have shown, that does not preclude obstacles occurring as a result of legacy of tropospheric default patterns at mid latitudes. An SSW is only effective 'in ones back yard' if there is clean cold air advection that is unhindered by 'left over' vorticity and also any legacy of sub tropical ridging pattern c/o low angular momentum... which, in my humble and less swashbuckling opinion anyway, doesn't make an -AO/ -NAO 'impossible to escape'. The record breaking SSW of Feb 2009 was seen as a 'dead cert' to a cold pattern - and it fulfilled that initial part of the bargain no question at all. But in terms of longevity, which you dismiss with ease as 'irrelevant' on this occasion, it flattered to deceive in terms of its undoubted long life being a quite unremarkable slow release valve - rather than any reloading deep cold nirvana. La Nina forcing on that occasion interfered with the mid latitude pattern which effectively cut off the -AO from sustained re-cycled lock-ins of cold due to the rossby wave train pattern from upstream c/o tropical forcing being scrambled by too much easterly inertia to allow a more typical +AAM signature southern stream to engage the higher latitude blocking and back the pattern substantively south and west. Once again this time, there is no doubting the size of the tropospheric >stratospheric momentum signal coming to fruition with this SSW. In my own un-exuberant way I have been a part of its evolution like very many others - albeit I admit and concede without ramping headline making It could indeed well be that the -ve zonal wind anomalies downwelled to the troposphere are strong enough to override La Nina seasonal inertia. I can see that for myself and could easily enough empty away the dregs of my glass and fill it up much higher instead and re-write this post to reflect the (obvious) upside All good then as you say. But as one who has looked closely and discussed in detail for several weeks ahead of this scenario the mechanisms that require the essential mid latitude dominoes to fall, I will be forgiven, for the time being at least, for taking much less for granted on the basis of preferring the polar field and the tropical cycle to have been, ideally, in better harmony The best forcing has just been and gone - its a pity the polar vortex wasn't sliced open then. Hopefully as you say that is an irrelevance and this post is long forgotten.
  6. As always, to try and take stock of NWP means instead of trying to second guess it (and its ensemble suites) at face value, it means instead attempting to step back away from it and try and do an assessment of the factors that are driving it These factors are vast and hugely complex to say the least and there is literally no-one who can make solid definitive predictions, (though some may try regardless of course), based on such an extremely loaded atmospheric profile that has been pulled in two quite different directions over such a relatively short period of time. But that loaded state still has to be assessed against the fairly recent history that has been equally as volatile as the present - and may still have a say in the way ahead in the context of the SSW. The Global Wind Oscillation plot orbit emphasises the contrasting forces that have been taking the atmosphere in two very different directions one after the other over just a ~ circa 6 week period. Two high amplitude directions - one opposing the other. . We have seen strong easterly trade winds from late December and the start of the New Year plunge the atmospheric state into a deeply low angular momentum state reflective of La Nina registering a stronger forcing relative to the official weak base ocean state. This beefed up a profile of sub tropical ridging and more enhanced polar jet flow that kept an average to milder in the south and often colder in the north zonal flow pattern flatter than otherwise might have been the case. Then, in complete contrast to this, a record breaking MJO amplitude wave has subsequently attempted to imprint on the top of the robust Nina profile of January, stretching the atmospheric profile in completely the opposite direction with a markedly +ve AAM disconnect to the base Nina state instead of a markedly -ve one . This has seen quite a change in the zonal wind profile across the Pacific with MJO derived +AAM anomalies replacing the swathe of -ve AAM anomalies (La Nina easterly trade winds) We have been seeing this tropical momentum process work poleward since the last week or so of January and the signals for stratospheric upheaval come into play to join the highly stretched rollercoaster of opposing forces the troposphere has been subjected to. I am deliberately paraphrasing and dumbing down the technical processes involved here to keep emphasis on the huge complexity and conflicting natures of the pattern. These technical processes have been discussed in detail over many previous posts anyway If we take the above GWO trace plot at the top of the post literally, then NWP to date has traced it perfectly. Flatter, faster zonal under the low AAM phases 1,2,3 during January - and then increasingly amplified in the last week as atmospheric angular momentum has shot up with the Scandinavian ridge of this week verified - viewed of late as generally as an appetiser to something better c/o SSW. So far so good. But this is where it gets very very difficult and why some caution needs to be applied in terms of trying to read between the lines of tropospheric reactions to the SSW The ying-yang of the atmosphere and its instability related to the fixed parameters that govern its wind-flow exchanges between tropics>extra tropics mid and higher latitudes>stratosphere) are working on an intricate series of different timelines that take the representative synoptic pattern in the troposphere to different places at different times. Its here that we cannot ignore December and January's past history as much as we cannot ignore the meltdown in the upper atmosphere that is up-comimg The Scandinavia block hasn't sustained (as expected) due to the brief nature of the peak of the +AAM spike above. The direction of travel is descent from here - but how much? This is discussed further down. But back to the context of the SSW for a moment, because global tropospheric wind-flows (as measured by the GWO) and the net outcome of those (flatter -ve AAM flow vs amplified +AAM poleward transport) are to be measured against the polar -ve anomaly easterly period at highest latitudes that the SSW will be yielding (over however many days it has technical reversal) There is surely no doubt that a high latitude block of some kind will emerge based on a reversal of zonal winds at the highest latitudes - it would be counter intuitive to suggest otherwise. But what is highly uncertain and questionable is how the whole troposphere profile responds based on the possible default tendency of the atmospheric circulation to default to La Nina once again as the latest amplifying poleward tropical momentum transport process concludes. We cannot assume 100% that the latest poleward forcing c/o MJO will automatically imprint a sustainable impact on the atmosphere (and hence the tropospheric synoptic pattern) based on this alone. Contrary to what is often assumed on here, MJO lags alone will not account for all this - we have to take the extra tropical reactions into account as measured by the GWO. On that basis we cannot make assumptions of sustained cold pattern verifications based on dateline convection if the extra tropical GWO is not conducive to this. Feb 2009 with its noteworthy SSW and very fast response time in the troposphere did not actually sustain anything like as long in terms of cold air advection to this latitude in terms of depth as its strength of destruction, but was instead diffused and watered down beyond the initial Scandinavian High pressure that gave the easterly and snow in the early part of February. There was something of a disconnect between the high latitude block profile over the polar field, and the pressure arrangement across our mid latitude which didn't reflect the type of classic -NAO response and undercut looked for in terms of sustaining a cold spell. Ultimately, a WQBO and La Nina profile thwarted any sufficient weakening of the +NAO profile. This winter so far, irrespective of E/QBO state, we have again seen how low angular momentum regimes when unsupported by amplifying actions of tropical MJO forcing (changing the traditional Nina profile of the Pacific trade easterlies) have easily reverted the atmosphere and tropospheric state to an unremarkable one at our mid latitudes. In many ways we are in similar place to where we were at the peak of the last tropical MJO phase in December - where the route to follow of AAM is always down - towards the return of the MJO to the Indian Ocean and start of the next phase. The difference to then, and it is of course quite a large difference, is that we have implosion forthcoming of the stratospheric vortex. Its hard to envisage absolutely nothing exciting happening isn't it? Isn't it? To take NWP into context, and why despite some charts which do suggest it will do what is expected and anticipated and yet others seem (almost annoyingly out of spite) seem to keep a stubbornly underwhelming profile, its necessary to look at how far angular momentum might fall back again at the conclusion of the latest MJO wave, however huge it has been and however imposing the SSW may look. Total GLAAM, relative to where it was at -3SD has sky-rocketed as shown in the timeline plot above - and best reflects the sheer size of the poleward tropical momentum transport that has taken it there. Another measure of the latest +AAM forcing is the Southern Oscillation Index (SOI) - spiking as much -ve now - as it was +ve during January https://www.longpaddock.qld.gov.au/seasonalclimateoutlook/southernoscillationindex/ The plot above for the GWO illustrates how rapid the orbit continues to race through the higher AAM phases - and this reflects the default reality that although showing distinct signs of decline, there still remains a La Nina signal firmly in the background to steer AAM budgets (net total global wind-flows) and suggest that an easterly trade wind bias *may* try to re-emerge around the time the SSW is trying to flex its effects in the troposphere. How much, if at all, this happens will have significance on the mid latitude profile and either offset or assist the tropospheric effects So its way too early to know, but any drop-back in AAM *might* be a factor that *could* work against effectiveness of blocking at our latitude and, such as happened in Feb 2009 under weak La Nina, with some residual splintered pockets of vorticity aligning some stubborn polar flow that scuppered sustained cold air advection furthest south- beyond the initial easterly. The significant snowfalls of that event are remembered, but what is less than remembered is that it was relatively unremarkable to follow Its hard to be sure at this stage, but set against the effects that the latest MJO will have had in terms of moving warmer waters eastwards from the Western to the Central and Eastern Equatorial Pacific, and also aiding upwelling of warmer sub surface waters (and hence limiting rather more any resurgence of easterly trades), then this, plus the legacy of +AAM anomalies scrubbing out so much previous easterly Nina inertia in the atmosphere should be enough to prevent angular momentum falling back too far. Ideally though, at least in my opinion, the best timing for the SSW would have been in the last 10 days, in tandem with the massive AAM surge and GWO in most amplified phases. All possibilities, including good ones remain, but I think its important to gauge the SSW against what has been and gone and how the cyclical nature of the atmosphere may influence (mitigate or enhance) the tropospheric effects of the implosion within the polar field. On a thread which is, alas, hyper sensitive to any pitfalls and resistance to anything that doesn't suggest cold - this is simply, as per usual, a little heads-up to the type of thing that might happen. Its because of this that so many of the key words are italicised. History always shows that such a sensitive emotional environment as this leads to all sorts of misconstrued and knee-jerk assertions further on. One cannot manage expectations and thrills and then disappointments for others for them, but it is possible to try to do ones best to tell them in advance. The rest is up to them.
  7. Remember reminder: Its only an island if you look at it from the water Feb 2018 : Massive poleward tropical momentum transport + tidal surge of +AAM tendency > +MT > fast orbit Phase 5/6 GWO Nino attractor in extra tropics (this weeks easterly 'jab around the edges') >stratospheric pathway dissolution/feedback from dateline convection > -AO/-NAO. Allowing for some deterministic model variations of forecast, based on the fundamental changes that are underway in the Pacific eastern and central waters, good supporting reason to 'cherry pick' the ECM to illustrate impending ultimate change downstream in terms of the state of Annular Mode I don't make forecasts as such, but lets just say the Global Synoptic Dynamical Model (GSDM) timetable is evolving very close to its defined timeline schedule from inception date ~ 22 January when the starting pistol was fired in the tropics c/o the MJO and the poleward momentum process was underway. The extent of the extra tropical +MT propagation sure reflects the huge amplitude of the tropical convection rossby wave trigger Back to a previous posted comparison made in last 2 weeks: Feb 1978: Spent most of the month in GWO Phase 5/6 c/o high amplitude MJO and led quickly to a strong -AO/-NAO combination. Differences? There was no La Nina lag underpinning an entrenched sub tropical ridge +NAO pattern and so the tropospheric/stratospheric pathway was unhindered to a much greater degree. Well, that and of course the absence of so much anomalous homogenous warming of tropical oceans which are skewing and rather neutralising the natural effects of strong tropical poleward feedbacks - in addition to the alarming atrophy of sea ice which correspondingly unbalances expected albedo feedback relationships to an increasingly unprecedented state : Feb 2018 is indeed proving to be a slower burner with, overall, increasingly less cold air relative to 1978 in the NH to share around in terms of cold air advection from the pole and which inevitably therefore favours much less dilution through continental landmasses like Canada, than downstreamacross oceans) But, all that said: There is an abundance of pretty cold air to the NW as we watch the next phases of trough disruption. Based on the spatial arrangement of cold vortices which look set to ultimately implode - that doesn't mean (by any means) that the UK and Europe won't yet see their coldest weather of the winter, as the end of official winter gets closer and closer March 2013 provided this on the Costa del Cinq Ports of the SE: It was even worth capturing some So, still very much the sort of thing that is more than possible late winter 2018, a few weeks earlier than the fun and games of March 2013 - and so there is no need for anyone to be miserable
  8. Posted this on 27 January: However, it still requires successful propagation of the added westerly wind burst (amplifying) anomalies that accompany the passage of MJO convection though the tropics, into the extra tropical mid and higher latitudes to facilitate widespread hemispheric pattern change. Its necessary to understand the lag times of frictional torque in the tropics > that lead mountain torque in the extra tropics - and then try to assimilate those conclusions as to when NWP might be impacted in the mid and higher latitudes There is then the question of how strong +ve mountain torque engagement perturbs the troposphere/stratosphere boundary I subsequently posted last week regarding suspicions of NWP and suggested that the evolution heading forward was a 'slow burner' for deeper cold which reflected emphasis of a theme of the last couple of weeks related to the eventual decline of the strength of Azores High (not yet happened as expected) and how timelines of soaring angular momentum tendency c/o poleward tropical momentum >extra tropics>stratosphere would be a key to changing this. An integral part of the 'slow burner' and necessity of turning the mid latitude +NAO La Nina forcing on its head MJO propagating eastwards through tropics>+ve frictional torque 22 January ( as posted last week) +MT (here and now)>stratosphere mid month. No links to plots from me this evening, or extravagant explanations (phew, they say). Just a (relatively) short post that keeps trust in continuity of more in depth on-going summaries of recent (and not so recent) times - and still leading towards what seems to be a remarkable consensus (across professional and amateur spectrum) of tropospheric/stratospheric meltdown. How that increasing likelihood manifests precisely in terms of 'weather' for this little Island remains to be seen of course. But my customary lack of flamboyant excited hyperbole and attempts at balance over headline grabbing doesn't disguise the genuinely growing anticipation of seeing where the 'jabs around the edges (we are currently seeing and as I described them last week ) ultimately lead to.
  9. It was well intended and well meant advice Taking NWP in the round, the stubborn persistence of polar jet energy (until now) flowing from upstream across the top of the Azores ridge has been indicative of a dominating +NAO pattern attributable to the lagged low point of atmospheric angular moment c/o La Nina forcing and stronger than average easterly trade winds since the turn of the New Year. Whilst there is not yet any undercutting -AO/NAO Feb 1978 type redux fully apparent - NWP is now, within the reliable period, adjusting the upstream energy process incrementally, bit by bit, as greater and greater downstream amplification is finally being realised. If we take another look at a yearly GLAAM anomaly, the size of the peak of the-ve GLAAM anomaly achieved is evident - which saw the La Nina strengthened trade winds ramp upwards. The atmosphere is now fast recovering from that low angular momentum regime and NWP attempting evolution of another Scandinavian ridge such as was seen in the first part of February 2017. That tropical momentum led +AAM anomaly spike, was discussed in a recent post, is clear to see again in the above 365 day chart for early February 2017 Back to ushering in Feb 2018: High amplitude tropical convection progression with rapidly rising AAM tendency has all but scrubbed out that -3SD GLAAM deficit ^^ - and still heading upwards. The atmospheric state is becoming increasingly conducive to +ve poleward momentum flux helping to amplify the tropospheric pattern more meaningfully. This leading towards a much better shaped H500 anomaly to externally destabilise the vortex. This, at the same time as internal +ve mountain torque forcing occurs - as a direct consequence of the poleward +AAM anomalies c/o tropical forcing propagating to the extra tropics and perturbing the troposphere/stratosphere boundary. To put some timelines to all this with the aim of helping explanations : If we take a look at the Global Wind Oscillation below, which should be seen as a measure of how the amplified wind-flows are progressing from tropics to extra tropics- then the initial signal fired from the tropics to start the process now unfolding in NWP was around 22nd January as can be seen by the plot (high amplitude GWO Phase 3 into Phase 4). This signal is representative of a surface +ve frictional torque which indicates the axis points where westerly winds in the tropics added by the forward movement of tropical convection start the initial process of scrubbing out the easterly trade winds responsible for the greater polar jet flow at mid-latitudes that inhibits amplification. The lag time for this +ve frictional torque and associated poleward heading +AAM wave flux anomalies to arrive in the extra tropics is ~10 days. Based on the starting pistol fired around the 22nd January, the GWO progression confirms this ETA of momentum in the extra tropics by the imminent expected orbit to the boundary of Phase 4/5 and engagement of a considerable size +ve mountain torque. See the added GWO template that confirms where these torque processes have taken place within the relevant phase progressions This mountain torque event has some highly interesting possible implications - not just for the amplification programme clearly underway in NWP into the medium term and increasing programme of cold air advection, but also in terms of the sharper NH hemispheric pattern which corresponds to assist external stratospheric meltdown. Such as stratosphere forecasts are playing peek-a-boo with. At this stage, what is interesting about the current evolution is that, *she adds with due caution* it looks slower and more sustained than Feb 2017. There are tentative suggestions of a slow burner, as the models keep adjusting the pattern further on into the medium term to one that is more meridional due to +AAM flux. It *could be* that the +ve MT delivers something of an icing on the cake from mid month. Something to keep watching out for in the longer term. Lag time for +MT >stratosphere/troposphere fall-out around 12- 14 days. This zonal wind cross section illustrates how the westerly wind additions c/o tropical forcing is impacting the rossby wave pattern upstream, with the emerging propagation of +ve shaded anomalies replacing the sustained bursts of -ve anomaly easterly trade winds evident across the Pacific since the turn of the New Year. This is another way of illustrating the switch from sharply -ve AAM anomalies to a contrasting swathe of +AAM anomalies impacting the extra tropics and as a consequence re-configuring the pattern from upstream with less strength into the northern branch of the jet stream - with more split jet flow and consequently greater trough disruption downstream - hence better mid to higher latitude amplification of ridging. The signs are emerging that the new travel of direction is gaining traction - with suggestions the models are contemplating a volte face towards a cold and blocked pattern with CAA ambush from both the NW and NE. As soon as this weekend. All rather confirming suspicions of recent days, and echoed in the semantics of the highlighted post above- that the flatter low angular momentum legacy might well be over-cooked. In that sense on-going NWP suites are simply snapshots in time to the evolution of the pattern playing out. Adopting this philosophy, it becomes more possible to watch what happens without unnecessary instinctive reactions to face value variations and swings within intra day operational modelling (and ensemble suites) I'm not sure that either of these have been especially instructive to any great distance of late. If the latest trends are anything to go by this is already obvious. Its not through it being my own model of choice based around preference, but because its the model that has been best fitting the pattern to the signals on this occasion that the UKMO has been leading the way and paving the evolution of the pattern into the weekend and beyond. NWP is starting to better matches the suggested GWO evolution of recent days and makes more sense (to me at least!) It does seem that an all-round catch-up is in progress and that might seem a (very pleasant) surprise to anyone who has taken NWP at face value in recent days
  10. received_10155821944031132.jpeg

    That's the way it should be - and you and her can have fun together about horsey things as Mum and daughter should!
  11. received_10155821944031132.jpeg

    They are beautiful. Those pictures take me back to days of mucking out at the stables, and getting ready for and then heading off to shows. I've never been riding in the snow though!
  12. The MJO continues to be referred to too often as a stand-alone product. Various analyses over a considerable period of time have tried to emphasise that the catalyst for change that does indeed come from the tropics in terms of organised macro scale deep thunderstorm development (the MJO) is just the initiation process. Albeit an important initiation trigger . However, it still requires successful propagation of the added westerly wind burst (amplifying) anomalies that accompany the passage of MJO convection though the tropics, into the extra tropical mid and higher latitudes to facilitate widespread hemispheric pattern change. Its necessary to understand the lag times of frictional torque in the tropics > that lead mountain torque in the extra tropics - and then try to assimilate those conclusions as to when NWP might be impacted in the mid and higher latitudes There is then the question of how strong +ve mountain torque engagement perturbs the troposphere/stratosphere boundary. Claims persist that too much is made about La Nina being a sole influence on the atmosphere, when of course it isn't. An E/QBO phase derives importance in terms of its ability to heighten efficiency of transfer of ozone from the tropical stratosphere to the polar stratosphere via an enhanced Brewer-Dobson circulation - http://www.ccpo.odu.edu/SEES/ozone/class/Chap_6/6_3.htm An enhanced BDC can help keep the polar vortex more unstable than under the W/QBO phase when it is generally less pronounced and the polar vortex strength is assisted by natural momentum gyre. We all know of how solar phasing has influences, not least how even moderate geomagnetic activity such as ushered in this winter, despite being in a descending phase, can still influence the height of the tropopause. Plus incidentally, because solar related geomagnetic activity influences the Ferrel cell, it augments the strength of the same sub tropical ridges that are a natural product of La Nina as derived by stronger than average easterly trade winds. So while we need to be aware of the complex jigsaw of factors, lets realise that many of them come back to the same common denominators that decide tropospheric momentum between the tropics and extra tropics. On that basis, one can return to the starting point of catalyst for MJO pattern change, and analyse the probabilities related to how the atmosphere may, or may not co-operate with poleward +AAM anomaly transfer into the extra tropics. The ENSO state plays a pivotal role here in terms of its base state because it tells you whether it is pre-disposed to low angular momentum inertia c/o higher easterly trade winds across the tropics that underpin sub tropical ridges and in our sector help support an +NAO, or whether greater westerly momentum added from tropical MJO forcing can help reduce the strength of those easterlies in the tropics and in turn, with time, also reduces the compensated strength of polar jet westerlies that blow at our latitude and inhibit development of blocking at higher latitudes. That last paragraph/ sentence in a nutshell puts us where we are with the NWP modelling. Over the last few days we have seen an increasing smorgasbord of solutions served up related to both assessed amplitude, strength and timing of poleward +AAM anomaly transport induced by a robust passage of tropical forcing to the Western Pacific. The strength of these westerlies (deep orange anomalies) in the tropics are now showing up impressively on the GEFS plot - and angular momentum tendency is on a re-surge from depressed La Nina territory. The last sight I had yesterday of frictional torque engagement of these on WDT (just before it was pulled!) reflected the GEFS plots and showed a very robust +ve upward tendency. On the way towards scrubbing out the considerable easterly wind legacy of recent La Nina forcing. However we have to factor in the lag times for poleward momentum transport and the existing La Nina surfeit in the extra tropics in terms of managing expectations for engaging changes within NWP If ever there was a time to clamour for AAM atmospheric budget updates it is now, to anticipate the extra tropical +ve mountain torque reaction and gauge possible strength of amplification as these wave eddies propagate to our latitudes On the basis of these complex equations, best not get hung up on the usual NWP upgrade/downgrade roundabout and enjoy the ride instead. I think that things may well keep getting more and more interesting. That is of course, if one is able to control instinctive reactions to intra day model suite variations - of which there will undoubtably be more to come Edit: That latest post from Steve Murr unfortunately exemplifies the type of baseless and unhelpful reaction that does this thread no good whatsoever. Its the weather- deal with personal frustration and inability to cope through a less tribal aspect.
  13. Hi there The best way to think of the Global Wind Oscillation is a plot depicted calculation representative of the never ending exchange of wind-flows between the tropics and extra tropics. Changes of velocity of momentum of these wind-flows create frictional convergence or divergence - and these are represented as +ve frictional torques where convergence occurs, and -ve frictional torque where divergence of wind-flows occurs. Based on the laws of conservation of angular momentum as @Bring Back1962-63 explains, coriolis angular momentum is affected according to whether there is greater easterly inertia in the global atmosphere (-ve torque and lower angular momentum) and which acts to slow earth rotation, or whether there is greater westerly additions (+ve torque or higher angular momentum) to the planetary system which assists the coriolis effect. Taking all these various momentum budgets into account, the GWO depicts the net balance of wind-flows at any given time through a plot depiction of atmospheric angular momentum according to whether there is greater easterly or westerly inertia in the atmosphere. Easterly (or -ve momentum) acting to decelerate global wind-flow means that the jet stream deceleration initiation occurs at the point(s) of momentum loss (divergence) This occurs across the Equatorial Pacific in response to the extra strength of easterly trade winds triggered by La Nina phasing. The divergence zone(s) across the Pacific act to encourage amplification of the jet where the deceleration of the jet creates a downstream vacuum . This amplification is manifested by the spin up the sub tropical anticyclones as underpinned by the low level easterly trade wind flow. The propagation of these trades spreading across the latitudes of the tropics under mature La Nina low angular momentum conditions further encourages sub tropical ridge amplification circum-globally to mid latitudes. There is increased westerly polar jet energy to compensate for the easterly inertia added from within the tropics - and these westerlies flow atop the northern flank of these mid latitude ridges in the Northern Hemisphere. The converse holds true for +ve momentum which creates a +ve frictional torque at points of wind-flow convergence. The best known macro cyclical and intra-seasonal phenomena of this type is the MJO - familiar to most readers of these domains. Organised deep thunderstorm development tends to naturally occur over areas of greatest heat and instability and these both trigger and are in turn triggered by further convergence zones - the effect being to propagate more activity in response to outflow boundaries much in the same way as micro scale thunderstorm multi-cells propagate and increase into batches grouped together. In this way, MJO progression patterns can be determined by ENSO phasing in terms of the spatial organisation of SST's across the tropical oceans. This is a dynamic and complex equation for anyone looking at long term or seasonal forecasting according to likely trends in these patterns. But the MJO, being a phenomenon that acts on reliably known repeat cyclical timelines,makes it possible to anticipate wind-flow changes that may occur at certain times as a result of forward moving tropical development and the resultant convergence zones they create - and which act to focus surface +ve frictional torque where they occur. At some stage these areas of tropical convergence are going to meet stable divergent areas (-ve momentum). The impact zone is where the forward moving westerly wind bursts that are associated with macro scale MJO convection meet the easterly divergence zone. In a winter such as we have this year, we see that the lines of battle are drawn across the central and especially eastern most Pacific where the coldest SST's are places according to the La Nina profile. This profile is rather further east than under many typical La Nina spatial arrangements of SST's and that means, in theory, that westerly wind propagation (+ve momentum) has greater chance of balancing the atmospheric angular momentum budget against the naturally higher weighted easterly trade winds that are the functional product of La Nina. Clearly there are many factors in play that are distortional to this and no one size fits all - not least, just as one example of variables, any solar geogmagnetic active state which plays a part in determining momentum of AAM through changes within the troposphere in the tropics and which can serve to boost the ferrel cell and augment further the process of sub tropical anticyclone strength that happens under traditional La Nina patterns. The plot depiction of the GWO organises the net state of global wind-flow into phase depiction according to low AAM (and negative momentum torque processes between the tropics and extra tropics) and also high angular momentum (according to positive torque momentum processes within the tropics and extra tropics) The spider graph these phases are overlain onto, are three distinct phases each for high AAM (Phases 5,6,7 or El Nino like) and low AAM (Phases 1,2,3 or La Nina like). There are also two 'transitional phases' which are indicative of momentum rising within or from a Nina state (Phase 4) and also one that is indicative of momentum in the atmosphere being lost within or from an El Nino type atmospheric state (Phase eight) https://www.esrl.noaa.gov/psd/map/clim/test_maproom.html Currently there is some uncertainty of speed of progression of added westerly momentum being added to the atmosphere c/o high amplitude MJO tropical convection heading on its way to the Western Pacific - so while GWO Phase 4 is currently indicated there is some question on the progressive indicated nature due to the lag times it takes for tropical >extra tropical propagation of additional westerly winds to start to influence the extra tropical mid and higher latitude tropospheric pattern The latest GEFS GWO forecast is added in respect of the above, and it will be highly interesting to see how the model plot depictions of the GWO dovetail with the tropical>extra progression of momentum that NWP is currently seeing in terms of expected amplification in the 10 day + period. At the moment there isn't clarity on this and the plot forecast is maybe a little progressive.
  14. Its only an island if you look at it from the water A textbook example of where an amplitude MJO wave lead the atmosphere on a surging poleward +AAM rally and which in turn created a bitterly cold high latitude blocked pattern from the first week of February and which lasted well into the month was in 1978 January 1978 closed out having featured a lot of the cold zonal pattern which has featured through quite extensive parts of this winter, and which favoured northern parts of the UK mostly. The very distinct difference back in early 1978 being that the global atmospheric circulation was pre-disposed to a Nino-like forcing which was setting in place a tropospheric>stratospheric pathway that was conducive to supporting poleward +AAM anomaly wave breaking. A reflection of how close we have actually come to achieving a properly cold winter in 17/18 - if the a-typical La Nina east based Pacific tropical forcing had prevailed and kept angular momentum in the elevated state it began the season. GLAAM: globally averaged angular momentum: Jan Feb Mar Apr May June Jul Aug Sept Oct Nov Dec 1978 1.75 1.75 1.54 0.81 0.17 -0.07 -0.27 -0.26 -0.22 -0.20 0.20 0.93 For info http://www.esrl.noaa.gov/psd/data/climateindices/list In a year as a whole that was to all intents and purposes of a neutral ENSO persuasion overall, I bolded and underlined the +ve GLAAM figures for all the winter months, and note how they are all book-ended early and late in the year. A further clue there how the classic finale in Dec 1978 evolved through further tanking angular momentum set against the base state, and renewed -AO and -NAO But back to what evolved in Feb 1978. Soaring +AAM induced the Global Wind Oscillation into the El Nino attractor Phases 5 and 6. The synoptic pattern moved into the sort of classic Nino pattern that can occur when the stratospheric field is weak and unstable (December 2009 is another very good example). Heavy convective snow showers for many, widespread severe frosts and culminating in those spectacular 'battleground' blizzards in the SW as the Nino feedbacks from dateline MJO forcing induced the southern stream and classic undercutting -NAO. Anyway, the point of all that nostalgic snow-fix is to illustrate the importance of having an co-operative tropical>extra tropical>stratospheric poleward loop in place to buoy the troposphere and to complete the task in terms of a stratospheric vortex which is vulnerable to such +AAM forcing. The skeleton troposphere/stratosphere pattern this winter at face value has been vulnerable to such forcing, but has so far achieved what would be considered a get out of jail card. Clearly, with the overriding La Nina forcing proving too strong, we have been lacking that missing link in the middle and why any high amplitude MJO wave, that becomes possible with the warmer waters in the western Equatorial Pacific, needs extra tropical co-operation to enable the troposphere>stratosphere pathway to be completed. In synoptic terms, effectively mimicking a wave train that is more akin to an El Nino and induce jet flow away from the polar northern branch, with weakened sub tropical ridges (that have been strangle-holding the on-going pattern), and instead energy flow into the southern stream assisting an -NAO. The coming month still holds a lot of interest - and one eyebrow at least is now being slowly raised. There is no denying the suggested strength of this MJO wave, which has actually been upgrading in prospects with time - and with signs emerging that this Nina maybe has been having its last proper 'hurrah' as sub surface waters in the Equatorial Pacific return closer to normal, then its not impossible on the back of the latest still increasing tropical momentum, that a significant +AAM surge might not evolve to lead the trend. In order to support that hypothesis however, some conclusive evidence from the extra tropics is required, and would be highly satisfying to see over coming days to prove that the undoubted momentum in the tropics is set to start putting in place the decline of this La Nina. To put that decline in its perspective, that means that the expectation is to weaken towards neutral heading into the Spring. But in that sense its not the base actual state that matters - its the direction of travel that would unquestionably make tropical/extra tropical co-operation more possible than it has been proving, and complete what has been the missing link. Lets hope its not too little too late - however if the direction of travel firmly becomes one of poleward +AAM that transfers on a sustained pathway out of the MJO tropics, then the chances of turning a frustrating pattern into something more interesting definitely increases.
  15. So, the attempted second guessing of the evolution of this latest MJO passage continues. In some senses there is nothing to add what was said yesterday and in so many recent times. Its really a case of not trying to look round too many corners at once, and simply let some more date evolve. The key point with this La Nina, like other 'east based' La Nina's is the eastward placement of colder water anomalies that promote a wind-flow pattern across the Tropical Pacific which is atypical to La Nina. The warmer waters in the Western Pacific and colder in the eastern most zone encourage a convergence of lower level winds in the central part of the Equatorial Pacific that is in opposition to the divergent winds I have spoken about (the latter of which promotes the boosting of the sub tropical high pressure belts in both the Pacific and Atlantic. The a-typical convergence zone feedback however triggers significant macro scale convective activity zone and triggers a rossby wave train pattern across the Northern Hemisphere. This tropical convection activity further east than under a typical La Nina, effectively triggers a wave train that acts more like it would during an El Nino. Hence that implies elevated atmospheric angular momentum set against the La Nina base state that replaces the low angular momentum synoptic imprint of sub tropical high pressure strength with a pattern that helps encourage a more -NAO profile The problem has been that this requires tropical/extra tropical 'co-operation that jives with the eastward shift of the ENSO pattern, so imprinting the feedback that overrides the traditional Nina Pattern. Thus far, the a-typical Nina theory that had proved itself successfully in other similar patterned winters such as 95/96 and to a degree also 05/06 has proved elusive this winter - though it seemed to be evolving successfully to a point at one time during December This is why I keep banging on about focussing on the GWO - because it is a measure of the co-operation (or otherwise) of the atmosphere to go along with the ocean feedback imprint adjusting further east than the typical Nina. On that basis speculating about the MJO and its passage eastward is only half the story. Sorry to repeat this yet again. If the atmospheric response (for reasons that are beyond the remit of this thread and belong in the learning thread) does not co-operate, then the traditional overriding La Nina response of higher than average easterly trades will continue to swamp any a-typical attempted signal. It will be the GWO orbit that will reflect the answer to this by either defaulting back to the traditional Phase orbits of 1,2 and 3 and would be indicative of the tropical element (the MJO) not drawing co-operation in the extra tropics. However, progression to the 'transitional' phase 4 is indicative that the east based pattern in the Pacific has drawn some feedback co-operation and has the effects of reducing the easterly winds that underpin the sub tropical ridges (the Azores High) in our sector and promoted a pattern more conducive to downstream amplification The updated GWO continues a slow amplitude progression across La Nina Phase 3 Furthermore there is evidence that tropical convection is engaging the signals with frictional torque heading upwards and angular momentum showing a robust re-bound. The greater amount that frictional torque is engaged in the tropics, the greater chance that +AAM anomaly will propagate sufficiently to spike +ve MT in the extra tropics to amplify the pattern But NB : Remember, whilst this AAM tendency spike upwards looks impressive, at the moment at least, it is only relative to the total low angular momentum state of which the deep amplitude GWO Phase 1,2 and 3 is representative of - and which has to be reversed by the process of MJO propagation in order to meaningfully amplify the pattern It now continues to be a watching brief of the +AAM anomaly propagation process c/o MJO forcing vs the base Nina feedback based on the analysis provided above, and which is consistent with the same analysis pointed out through the winter so far
×