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Tamara

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  1. Tamara

    Teleconnections: A More Technical Discussion

    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
  2. Tamara

    Teleconnections: A More Technical Discussion

    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.
  3. Tamara

    Teleconnections: A More Technical Discussion

    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.
  4. Tamara

    Teleconnections: A More Technical Discussion

    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..
  5. Tamara

    Teleconnections: A More Technical Discussion

    And so this has proved In fact the atmospheric ying and yang that has built blocking programmes, and then further re-built them, has continued unabated for some quite considerable time. A time that encompasses the east based La Nina of this time last year through to the ultimate arrival of El Nino at the close of this year. The GSDM is a diagnostic tool to assist shaping numerical model forecasting all year round and not just applicable to fitting to winter time weather patterns (and preferences). To this end, back in the summer I was persistently espousing on another site the key link between substantive programmes of poleward +ve AAM momentum transport as triggered by eastward propagating tropical convection that lead to surges of relative atmospheric angular momentum tendency and, as reflective of this synoptically, blocking at mid and higher latitudes (subject to changes within the polar field seasonally) through global>regional rossby wave dispersion. Classic tropospheric driven pattern changing sequences. If we look at the last 12 months, we can see this process has happened several times at the various different times of the year. Programmes of repeated amplification related to the GSDM mechanisms augmented by : 1) Persistent episodes of MJO related macro thunderstorm development and organization - with the breeding grounds for these being the migration and upwelling of warmer waters assisted by repeated convectively coupled kelvin waves. The depth of the convergence zones created by these macro size linearly organized convection zones, resulting in ever increasing strength of westerly wind bursts in association with the eastwards progressing strong convection setting up frictional torque eddies where they meet opposing (and submitting) trade wind-flows. The increasingly east based nature of the previous 2 year La Nina regime extending into the early part of 2018, encouraged such convergence zones to develop further east across the tropics than under a traditional La Nina, and are now even more conducive to dominance and strength under a burgeoning highly coupled ocean>atmosphere connected El Nino. Such sequences have repeated during Jan/Feb as attributed to help triggering of the SSW in Feb 2018 and the associated severe cold across parts of the NH. Then, on a less extreme scale at different times during the late Spring and mid summer. Notwithstanding that, still perpetuating the anomalously strong mid latitude sub tropical blocking patterns that prevailed throughout this period and produced equally anomalous and persistent heat in many parts of both Europe and the US. 2) The relative stage transition of the easterly QBO to westerly QBO is currently at peak efficiency in aiding a robust Brewer Dobson poleward circulation and distribution of ozone between the tropical and polar stratosphere. In tandem with the tropospheric +AAM transport programmes as described above, this has allowed the mid latitude blocking regimes dominant under a +AO/NAO regime seen the middle of Spring to transfer into a highly unstable troposphere/stratosphere led relationship that is strongly compliant towards developing a higher latitude blocking regime. The El Nino tropical>extra tropical blue-print propagation of +AAM anomaly eddies also switching jet stream flow into the southern stream as a key part of the mid latitude NAO switch, that is the one part of the changed Annular Mode coupling 3) Spatial distribution of arctic open water vs highly vulnerable sea-ice - creating feedbacks alongside diminished solar cycle state, to enhance further the very highly amplified tropospheric/stratospheric disconnect relationship There is clearly a lot of evidence to support all these feedbacks sustaining tropospheric/stratospheric disconnect through the foreseeable period and beyond. Many of the excellent seasonal assessments and general thoughts expressed by members, who all will be familiar with on here, have covered these in great detail Objectivity demands looking at what might change this as well as might allow it to persist. The times we live in, with so much background climate forcing skewing both tropical and polar feedbacks make relying on analogues a precarious business. Nevertheless, in terms of comparison, amongst them its possible to look at 2009/10 - at least anyway in terms of the tropospheric/stratospheric disconnect that developed on cue with the arrival of winter amidst similar evolving El Nino driven momentum transport programmes. This year is actually already advanced in relation to that year with the troposphere highly dominated already in November by poleward +AAM momentum processes - and the Global Wind Oscillation echoing an El Nino ocean>atmosphere connection with orbit into the Nino attractor phases 5,6 and 7. This type of sequence, and not too dissimilar synoptic imprint, was echoed during December 2009. It is unfortunate that we still cannot access the updating GWO orbit map-room which as been "down" since mid October, but its still quite possible to ascertain the likely tropical>extra tropical GWO plot depiction of global wind-flow budgets through torque interactions relative to angular momentum tendency transferred with time into total globally averaged atmospheric angular momentum. This confirms that global westerly wind inertia is now significantly ascendant of weakened trade winds and OLR patterns and other proxy indicators are starting to reflect the Pacific driven pattern. The NH synoptic pattern representative of this with both Pacific and Atlantic dominated by southern stream orientated cyclonic anomalies and with the representative downstream blocking regimes assuming a higher latitude placement in accordance with the disconnected and unstably warm tropospheric /stratospheric profile. With the inter-dependant variables being clearly not precisely in synch with the likes of 2009/10 however, caution is required in blanket assumptions of lower and upper atmosphere disconnect persisting throughout the season this year, such as they did then (and supplemented by an SSW such as happened in Jan 2010 when the upper atmosphere was as a consequence unable to percolate its previously anomalously cold layers into the unstably warm tropopause that had dominated the first half of the season) Its far too early, at least for me personally, to produce any confident suggestions as to how the long term may proceed. I do not profess anyway to put together seasonal forecasts but rather defer to my own little informal style of individual shorter periodic summaries of thoughts . Such is this one of a type I previously produced on another site every other week or two up to the end of this summer. But consensus is already quite strong this end period of the year that a traditional El Nino influence under tropospheric/stratospheric disconnect may lead, under natural seasonal wavelength changes to augmenting further an increasingly cold air advection regime in the first half of winter . To put it another way, an amplified GWO progression through Nino attractor phases in November produces a highly amplified pattern under stratospheric weakness and taking all the ongoing interdependent variables into account. This can only be magnified heading through December and most especially into the start of January. A curve ball to this would be an -ve AAM atmospheric>ocean disconnect developing appearing during December which would hand some initiative to switching some energy back into the polar Jetstream, scrambling the higher latitude blocking mechanism and allowing the tropopause layers and seasonal polar vortex to re-group to some degree. At present there is no sign of this and as reflected by the analysis given, not much background support to it happening, but bearing in mind the "mini ENSO cycle" has natural wax and wane periods within the general larger hemispheric trends, its something that is always worth keeping in mind. And it is also something that has happened in other seasons such as during December 2012 to 13 when a weak stratospheric vortex was able to re-group due to falling angular momentum in the lull phase of the tropical/extra tropical cycle (and also amidst a spike in solar activity during an otherwise weak activity regime). Less confidently, or perhaps more speculatively, the associated volatile high impact weather regime resulting from the ascendance of the polar field influence to mid latitudes (and its rapidly changing cold/warm boundaries c/o southward displaced jet stream) ultimately might lead to an implosion and anomalous warmth later season as sub tropical air floods more generally northwards and meets fragmenting upper cold pools withdrawing in its advance. Its hard to be too specific, but late winter season El Nino's sometimes align with further seasonal wavelength change to produce this type of response following weak stratospheric vortex domination and as the ferrel vs polar cell relationship starts to shift ahead of Spring This also is the time the +ve QBO transition maybe most likely to finally capitulate to upper westerlies - ending the unstable lower trop/strat disconnect. Should this type of evolution come to reality, and it is obviously highly subjective at present, the timing of it remains a moveable feast either side of the spectrum. Bu way of concluding this post and as means of acknowledging the highly positive environment of this site: The role of teleconnections, not least perhaps more especially the GSDM relationship to all inter-dependant interacting variables (at any given time) continues to be misunderstood and indeed misrepresented across some quarters of both the professional and amateur spectrum. However, I would fully endorse, like many others, the page header articulated so emphatically by @Isotherm that "this board has unequivocally risen to the pinnacle of atmospheric science discussion" There is left no space in my opinion for parochial attitudes and discrediting that are sometimes framed by personally driven agendas and too much pre-occupation with weather preferences vs cold realities of the science, and that obstruct the path to engaging learning and progression of further learning. The members, and they know who they are, that have put in the hard work to lead to creation of an ambitious library portal that will remain an ever growing "work in progress" advancement - has been encouraging private reading that can now being supplemented by the various amateur and professional minds who are migrating to this site and providing reality equations in the here and now to all the research papers. Reality equations that help make sense of all the complicated scientific speak contained within these papers and where often the prescient needs are found with a few paragraphs and sentences. The administration of andrain are to be very highly thanked for encouraging and allowing such initiative to develop and flourish - and without ever needing to feel they have to exercise their own authority in overseeing and controlling it. They also encourage a level playing field and never discriminate between different learning types and approaches. No-one is ever judged publicly to be too vague, brief or ill-informed. Neither are they discredited, demeaned, or dismissed as guilty of spurious waffle in the innocent desire to provide informative and thorough explanations An example for all weather related media and forum affiliations to follow
  6. Tamara

    ***Winter Countdown Thread 2018-2019***

    Predictive models are prone to bouleversement due to historical imprinting as well as inherent forcing biases. Stochastic as well as deterministic approaches are required here to help sample associated uncertainties under discussion. A *supposed* end point (f.e SSW) can be part of a numerical model deterministic prediction, but it requires a probabilistic assessment of the suggested route to get there that involves different possibilities evolving on the way. Eagle-eyes are also needed on GSDM lagged timelines, as an insurance reality check applied to assumptions made about future torque responses. So this means that care is needed when plotting both the diagnostics within the GSDM itself, and also the numerical synoptic responses ahead that are attached to them . The extra tropics may yet to be to respond to +AAM anomalies triggered by westerly wind bursts still propagating from the tropics. So its not always about present index values (and numerical model forecasted teleconnection values need most extreme care - sparing assumptive pitfall errors through a required reality check GSDM diagnostic applied to them first). Most importantly of all at the moment - scrupulous watch of the tropical/extra tropical interchanges are very key, as the precise relationship the atmosphere is adopting to the ocean base is highly dichotomous, and recent CCKW activity in the Pacific has been most rambunctious seen thus far in 2018 which suggests that reading between the lines and keeping an open mind is required when considering future atmospheric response.. I would proffer that the potential disconnect posed by this dichotomy is unsustainable indefinitely (within the major ENSO life cycle). Whilst an unstable GSDM disconnect profile visible through the GWO reflecting AAM variations due to opposing torque lags and rather idiosyncratic conflicted momentum transport may exist in the shorter term, the Pacific ocean tumult relative to CCKW elevates more and more the risk of a substantial atmospheric response through eastward moving amplitude tropical convection with time . It is this that poses the maximum early *potential* polar stratospheric vortex threat through dispersion of rossby wave eddies aggregated c/o robust tranches of +ve poleward momentum transport. Profound ocean>atmospheric coupling events often presage final endings and new beginnings of ENSO phases, and are often associated with high impact weather repercussions at the surface as ruthless adjustments to the AAM budget within the atmosphere take place. Substantiating the pitfalls present., it is also prudent as always to be mindful of the fact that tropical convection deterministic models are extemporaneous and viccissitudinary in their forecasting ability more than just 5 days ahead - so I would be keeping a close eye on the potential for a November flare-up of the sort that would leave any remaining stubbornly resistant easterly wind-flow aka Nina-like inertia resistance obsequious in capitulation. Taking into account the present solar forcing disposition, I think that the current QBO transition in association with this, is pinnacle in assisting a maximised tropical convection response, and history shows that these are often incircumscriptible in the profound effects they can manifest tropospherically and stratospherically - as well as being highly symbolic of concluding transition timelines of ENSO phasing through imprinting the ocean CCKW effects of warm water upwelling and propagation. Ergo: the arrival of El Nino.
  7. Tamara

    Teleconnections: A More Technical Discussion

    To be most precise, the typical ENSO timelines mentioned in the caption above are best fitted within the framework of the Global Synoptic Dynamical Model and broken down into its components that comprise short to medium time leads determined by the "mini ENSO cycle" (typically 30 to 45 days within the tropics and up to 60 days timeline feedbacks from tropics to the extra tropics) - and then longer term and intra-seasonal feedbacks of up to 90 days and more which comprises a further "mini ENSO cycle" and cyclical feedbacks stemming from elements of both the first and second mini ENSO cycles. This, a rolling programme that evolves constantly into the future as a means of extrapolating how the atmosphere and the ocean keep developing their relationship according to the direction of travel of the ENSO signal This relationship can be likened, in principle, to that of the troposphere and the stratosphere (seasonally dependant). The ocean and atmosphere can also exist in a coupled state and/or they can exist for periods in disconnect. So there is no linear x+y= progression of any given ENSO event, as it is the precise relationship that the atmosphere adopts to the ocean base state, at any given time, that is determinant and not the base state per se self evolving as a lone entity. I believe this post further down will illustrate the ENSO evolution of 2018 thus far as a case in point Subseasonal forcing can either be augmented or dampened by the relative amplitude orbits of both tropical (MJO) and extra tropical (GWO) elements of these mini ENSO cycles. It is the augmenting and dampening of these that require initial consideration as the net outcome of these processes in turn reinforce or dampen a pre-existing (or existing) ENSO signal In essence each event, each case, each evolution has to be taken on its own merits and summarising ENSO processes in overview terms requires this type of approach. Another example of where analogues can be flawed (not least when long term trends in temperature and skewing of feedbacks from oceans and the pole are taken into account.) So the purpose of the GSDM within the context of the mini ENSO cycle is to constantly calculate the wind-flow exchanges (net westerly and easterly) that occur through torque mechanisms and result in changes to atmospheric angular momentum tendency (in simple terms this manifests synoptically as a calculation of the turning force of the jet stream). The consolidated data available from the GSDM provides a diagnostic tool to NWP in terms of plotting wind-flow inertia (easterly/westerly) and associated deceleration of the jet (easterly inertia) and accelerated velocity (westerly) - but it also provides a measure of how the atmosphere is responding to the ocean forcing and whether a connect or disconnect exists. Closely monitoring this data is a highly useful way of watching how this relationship is evolving The micro diagnostics involved form the basis for shaping increasingly macro diagnostics according to the timelines broken down within both mini and macro ENSO cycles. It therefore becomes possible to retrospectively examine whether easterly or westerly winds have been most dominant over time through an examination of trends in angular momentum tendency and to give an assessment as how successfully periods of WWB's have been in progressing a trend towards a Nino-ish reflection of atmosphere>ocean relationship as is relevant to 2018 (or vice versa according to direction of anticipated travel of the major ENSO cycle at any other time) A look at angular momentum trends since the late Spring, when the oceanic La Nina standing wave was releasing its two year grip, shows that the transition phase of this ENSO cycle has been anything but linear progress towards a destination El Nino as far as the atmosphere is concerned. Taking the whole 120 to 150 day trend, it has been low AAM (La Nina-like) dominated overall. And still not convincingly +ve to date with other indicators like the SOI distinctly well within neutral range (+8 to -8) despite briefly in early October registering its most -ve intra days state since the strong Nino of 15/16. This statistic rather emphasises how Nina dominated the atmosphere has been than suggest anything significant at all about the progress thus far of this El Nino Its clear that following tropical convective forcing in the Pacific which spiked westerly winds, recovered AAM tendency and aided progression of SST and sub water propagation of warmer waters in the second half of July.... …., that these westerlies were quickly scrubbed from the atmosphere and easterly trades took domination, ( albeit weaker than the early summer) for the late summer and early part of this season. While various pro Mets and some seasonal modelling has kept ramping up progress and making predictions about El Nino (that have kept correcting back in time in reality) its only been in October that we have seen any meaningful resurrection of westerlies and associated upturn in AAM to give renewed indication that the atmosphere is trying to get back on track towards the Nino standing wave becoming the dominant established force as predicted by guru's and models. So up till October its been more a case of one/two week of WWB's in late summer that successfully gained ascendency and reflected greater westerly inertia in the atmosphere than easterly. This month has shown what may well be the most convincing progression towards some credent support to seasonal models that have documented development of at least a weak El Nino this coming winter. However, taking the previous 90 to 120 days (and more) that has comprised the evolving ENSO transition (thus far) then more than several weeks at a time has seen greater easterly inertia than westerly. The AAM plot evidences this in terms of the net -ve momentum deficit to the atmosphere (and the Global Wind Oscillation which reflected this supressed AAM state with orbits in the Nina phases 1,2 and 3) This is mainly a post of trying to add some further substance to the interesting comments of the quoted one, but also to add some true perspective to the reality of a quite apparent stubborn disconnect evident between the ocean and the atmosphere - of which assessments that have kept and keep proclaiming a Nino state need to acknowledge when making forward assumptions about this coming winter - even if progress does finally seem to be getting on track. There is simply no x+y= relationship and as with NWP its the case that signals lead models, models don't lead signals To conclude this post :- As a real-time example of the GSDM defining Pacific jet flow, we can look at latest two day lagged mountain torque plots to check the progress of a tranch of easterly winds that propagated from the tropics in the past 10 to 12 days finally impacting the extra tropics and register a -ve tendency East Asian MT This addition of easterly trade winds to jet flow results in a sudden deceleration (scrubbing of surplus westerlies as indicated by previously +ve EAMT on the plot and where the vacuum is immediately left in the atmosphere c/o switch from +ve to -ve EAMT). A key retrogression domino downstream synoptic sequence occurs as Mother Nature fills the vacuum - the pattern consequences of which currently see weather impacts changes for US, and also many parts of Europe including UK who are downstream of a l/vw significant amplification of Atlantic ridging pulling down a first incursion of arctic air in origin of the season as part of the retrogression response Whilst the lagged effects of this easterly -ve torque low velocity momentum are feeding through at the surface, the atmosphere is already responding to latest surge of WWB's to perpetuate the ying-yang effect on thr atmosphere. Frictional torque is trending upwards (at the inflexion point of where these added westerlies are now scrubbing out easterlies) and taking into account further approx 10 day timelines of frictional >mountain torque tendencies, a subsequent increase back to +ve momentum transport is set to reverse the retrogression phase. Atmospheric angular momentum tendency has already responded very sharply upwards from the -ve tendency associated with -ve EAMT.... ….and as the retrogressive phase still plays itself out ahead of the sudden momentum set to push the wavelength of the pattern back again. For example, gone will be the currently highly amplified ridge in the Atlantic sector and is set to be replaced by a deepening upper trough in the 10 day period as upstream momentum feeds through. One or two posts I made in the last two weeks or so documented the likelihood of how NWP modelling was likely to overdo the initial retrogression signal and then get spooked by the added momentum transport signal immediately thereafter. This has proved reasonably accurate I think model performance of late has reflected this with some problems resolving the tropospheric impacts from two contrasting momentum scenarios, but also especially wrt to within the polar stratosphere which is being invaded by some contra intra seasonal complications NWP is now reflecting changes into November as the models start to 'see' more clearly the signal already well advertised ahead by the GSDM torque and AAM budgets. Utilising the diagnostic framework of the GSDM can assist assessment of the ocean/atmosphere relationship in context of ENSO (both retrospectively and moving forward) but also in real-time modelling shape some thinking about how changes in velocity and vector of global wind-flows, as expressed by torque mechanism in the tropics and extra tropics, will impact the jet stream and as a consequence influence movement and placement of pressure systems
  8. Tamara

    Teleconnections: A More Technical Discussion

    A nice summary from David Further to his thoughts, a good time to look at some more torque analysis to try to flesh things out further. The eagle-eyed may have spotted some interesting current contra-indications between frictional torque tendency in the tropics and mountain torque tendency in the extra tropics. Recent westerly wind burst activity across the Pacific is identified by the Asian jet extension as identified by the +ve EAMT (red line) At the same time as per the plot below, and in contrast to the extra tropical Pacific, frictional torque tendency is more and more -ve in the tropics To dovetail with David's analysis, most of the -ve tendency signal is reflective of loss of westerlies scrubbed from the atmosphere at the expense of easterly trade winds c/o low frequency tropical signal fading across the Indian Ocean. Frictional torque is turning increasingly -ve (now down to -2SD) in response to this with an inflexion point focussing around 20 to 30N We know that frictional torque tendency is a good cue for the future direction of travel of mountain torque tendency taking into account the timelines that the GSDM offers us. As these easterlies propagate polewards towards the extra tropics over the coming ten days then this looks primed to reverse the +ve tendency flow off the Asian continent and synoptically manifest as quite a strong upstream amplification signal across the Pacific. This is a set-in-motion deceleration of momentum transport that also amplifies the l/wv response in the Atlantic sector as the downstream pattern response is to retrogress the further anomalous mid latitude ridging presently over Europe. This is now quite well advertised in 10 day + model ensemble means. No latest updates from the GWO since the 14th (and subject to two day lag) but progress is totally accordant with recent movement as posted above by David into Phase 8 - this representing the start of loss of accrued westerly inertia from the atmosphere. I cautioned recently that the models might overdo this signal in relation to the background to GLAAM vs the emerging Nino standing wave. There is little doubt that a retrogressive pattern will feature heading into the last third of this particular season - but matters become problematic and uncertain based on future low frequency tropical convection patterns in the light of the biggest convectively coupled kelvin wave of 2018 to date in progress in the Equatorial Pacific These events very typically feature a lagged sharp coupling correction response from the atmosphere that is manifested by an amplitude Pacific low frequency tropical convection event - the westerly wind burst advancing as part of eastward progression of tropical convection and serving to sharply arrest easterly wind 'destructive' influence of trade winds to the continued attempts of spatial SST and sub water warming across the ENSO regions. The CCKW is the big ocean signal - it requires the atmosphere to imprint it and help initiate El Nino as described. There is no sign of this at this time, but models are especially poor and unreliable at long range MJO forecasting and its something to watch heading through later November. We should also factor in that ahead of impending correction, GLAAM recovered from the post late summer slump back to +1SD above parity recently - albeit it is responding slowly now to the -ve momentum tendency phase that is beginning as described. This is the benchmark to gauge the start of consequent fall and then next recovery from. I would add in this respect that the AAM CFS and GFS model forecasts for relative atmospheric tendency need to be taken with caution. These forecasts have not proved reliably accurate of late vs the verified consolidated GSDM data and the latest (actual vs forecast) -ve torque tendency alone as posted above is not reflected at all in those forecasts Taking into account all the above factors, an unstable period of AAM/GWO patterning may lie ahead - with the long range models in the coming month quite conceivably spooked by the spectre of a downward lunge in angular momentum (upcoming retrogression signal) followed by a bounce surge back upwards to follow with another wall of westerlies subsequently splintering any defence of easterly trade suppression in the Pacific. The CCKW as discussed has relevance to this later development. Factor in also the progression of +QBO descending the layers of the atmosphere, then an increasingly very cold upper stratosphere maybe will be duelling with an early season unstable disorganised lower stratosphere/upper troposphere that at the same time also blind-sides the models to the consecutive double-whammies of contrasting rossby wave dispersion momentum transport fluxes. Whilst we cannot be sure of precise synoptic patterns to evolve with so many complex factors at hand, if we furthermore include the possible arctic sea ice pattern progression ahead that James @Singularity discusses - then combined with an unstable GSDM/GWO orbit profile, and a potentially highly contrasting top to bottom polar stratospheric field profile, then it increases the likelihood of high impact weather events for the incoming seasonal cusp change period. Such impact weather manifested as large global>regional contrasts of temperature/ppn through competing torque mechanisms creating a cocktail of wind-flow eddies and perturbed jet flow orchestrating with a stratospheric vortex that may exhibit some confused double identity before, maybe, settling into a more familiar +QBO pattern thereafter. Plenty to look out for - time as always will tell
  9. Tamara

    ***Winter Countdown Thread 2018-2019***

    A response to offer some added perspective to this tweet as was posted Any -ve mountain torque response is a signal that atmospheric angular momentum tendency is falling due to an increase in easterly trade winds occurring This acts "destructively" at face value, or more accurately and realistically at least interrupts the progress of warming of SST and sub surface anomalies across the ENSO regions Not what most folk on this thread I expect are hoping for. It does so, by scrubbing out the westerly wind bursts that propagate poleward through +ve torque momentum and which are an important part of the process to achieving programmes of amplification across the mid and higher latitudes This poleward +ve momentum transport c/o +ve MT being the type that produced the SSW last winter to produce the more sustained and deeper cold air advection potential (rather than the cold shots that temporary mid latitude amplification such as this captioned scenario advertises) In itself, the sequence attached to the above tweet is not a big deal as part of the natural ebb and flow of tropical convection patterns as part of the "mini ENSO cycle" - but in terms of the shorter term context any colder shot potential associated with a retrogression of the l/wv has to be taken in the context of how seasonal wavelengths will change this response anyway heading into winter and put the cold-shots produced by it into context against a pattern that would be likely +AO/+NAO in origin Seasonal wavelength changes heading into winter suggest increased energy moving into the polar jet, assisted by chances of a more organised vortex under a regime that would occupy Nina-esque characteristics set against a weak ENSO state and increasingly +QBO That description isn't the reality, clearly at this time, but its a suggestion of what might happen assuming the same scenario in a couple of months time when winter proper is arriving Ergo, a -ve torque response (effectively a La Nina type forcing) is counter intuitive longer term to the processes that most are looking out for in terms of the tropospheric/stratospheric pathway to a destabilised vortex that benefits the East Coast (or those in Europe for that matter - maybe especially more so because the dependence on a -AO/-NAO is even greater to advect cold air to latitudes this side of the Atlantic) But its the bigger picture that is more important still in terms of long term trends when we consider that GLAAM has only recently broken at +1SD above parity for the first time since, very briefly, in late July. A good graphical measure of how progress, in reality, of this El Nino standing wave has struggled to develop within the atmosphere, despite all the bullish ENSO seasonal forecasts that have prevailed throughout this time. And still continue to, apparently, upgrade... I'm not one to personally produce or attempt to produce forecasts for reasons that hopefully are self evident from this post,, but I still think its a sensible cautionary word not to over rely on models to verify at what they suggest at face value at a given time ENSO modelling, and that also includes bureau updates from organizations over the progress of ENSO trends, both tend to be reactive rather than proactive to events ahead - and in truth ( at least in my opinion) with background warming trends that are both seriously skewing feedbacks in tropics and arctic alike, there is also caution needed with dealing with using forecasting analogues (especially older ones) as well. Additionally to that, short to medium term deterministic modelling is poor at dealing with MJO and tropical forcing, let alone relying on seasonal pattern models to read them up to a few months ahead. If amplitude and orbit of tropical convection is misread within a week or two, what hope for accuracy extrapolating outcomes over a season ahead and which tropical patterns have such an impact on far and wide? Of course this is not to totally devalue numerical tools - as sites and threads like this would not bother to exist, but its yet another reason why I personally rely on proxy date checks for atmospheric circulation response, especially the invaluable framework of the Global Synoptic Dynamical Model, to give consolidated real time data as to what is happening c/o of atmosphere/ocean relationship rather than eschew the biases and climatology issues of numerical models. In short, signals lead models. Models don't lead signals. So, as customarily adopting the GSDM, what is the latest analysis : As stated above, total global atmospheric angular momentum is slightly +ve - led by EPAC standing wave activity generating +ve westerly wind momentum. In reflection of this, there has been tendency of +EAMT up to now However, though there is some model variation, the consensus is for the MJO is imminently expected to lose eastwards progression across the I/O and lose signal and amplitude before (subject to model performance caveats) an emergence back in the Western Hemisphere. This loss of eastward progression of present activity results in westerly winds scrubbed from the atmospheric circulation as easterly trades are increasing somewhat close to the DL Tendency in frictional torque, which leads direction of travel of mountain torque, is slightly -ve as a result of easterly inertia interrupting the w'rly wind bursts across the Pacific The effect of falling torque tendency is falling AAM tendency.... …..and deceleration of the jet stream from upstream. Hence, taking into account the timelines of torque changes between tropics and extra tropics of circa 10 to 12 days, NWP is programming the Pacific amplification and retrogression of the l/wv pattern in response to this ( as per tweet). The upshot of all this is that the Global Wind Oscillation, which is a plot depiction of total windflows within the tropics and extra tropics is heading from pre-transitional El Nino Phase 4 back towards pre-transitional La Nina Phase 8 as relative angular momentum falls back as cue for indicated retrogression Taken in context of (albeit slow) progress of this Nino, and total angular momentum reflective of this at +1SD - then I think there is a chance that the models may be too progressive with the retrogression and caution needed with how far any migrating trough digs into the US (and especially ahead of the Atlantic ridge response further downstream that also corresponds to a downstream trough response into Europe) For the majority on here looking at snowfall chances ahead, its my opinion that October/November colder incursions are worth sacrificing for a developing El Nino regime that might imply a warmer lead in, but much more likely to teleconnect in a more conducive way to tropospheric/stratospheric disruption (but attendant with +QBO risks) and longer term cold air advection potential when the time will deliver optimum results for those hoping ahead. Its going to require the GWO orbiting into Phases 5, 6 and 7 to indicate a full El Nino atmosphere/ocean coupling has occurred and all that entails with the seasonal models - that is yet to happen in any way at all other than a brief half hearted attempt in late July. The GWO has actually spent more time in the Nina phases since then, at low amplitude, till the most recent attempt to adopt a more Nino like response, So the upcoming lull phase of the ENSO cycle, with some possible further interruption to the Nino progress, is important in terms of where GLAAM currently sits and how much of a rebound in AAM can occur thereafter to resume progress. This will give clues as to how much rossby wave dispersion the troposphere is able to supply in terms of -+ve AAM transport as the stratospheric vortex continues its natural cooling process into what is the main season of interest in here. At the moment, at least from my own point of view, and for what little it may be worth, there still remains uncertainty attached to the actual relationship the atmospheric circulation is set to adopt to the ocean base state - and that leaves the seasonal modelling (whatever the various suites suggest) requiring a little bit of salt being needed to apply to them. This is because there remains a gulf between what the models forecast, and what the atmosphere is currently actually saying and which remains not totally convincing in my opinion (yet)
  10. Tamara

    Historic Category 4 Hurricane Michael

    I live in another country but also in a coastal town where structures haven't been updated for, um, shall we say, quite a number of years for some of the same reasons quite likely that Mexico Beach retained its own old charm. Even if the weather on this particular SE coast is quite obviously less sub tropical than the Panhandle of the US SE coast. Its hard of course to put yourself totally in the shoes of people who have been devastated first hand by such a terrible event, but I think I can get my head around why I might contemplate riding out such an event in a small community that is kind of in something of a time warp. I can relate to that at least - and also a lot of such folk live simple lives and look out for one another in a way that is not so easy to happen in large urban busy city lives were people are less inclined to notice one another because of the different style and pace of life. Just saying Also, as would be the case anywhere regardless of location and type of location, there will be people who have circumstances that don't allow them to leave on the flip of a coin. I agree its is a warning for the future - but in a world, especially countries in the "richer world" , that isn't always the best at carrying its most vulnerable with them (very much including unfortunately the country I live in) then maybe the lesson is to care for them better first an foremost and then perhaps the debate about improvements in the face of the challenges of more frequent and intense "severe weather events" (of all kinds) might be on a level playing field that allows progress to be made in a way that supplies answers more naturally and automatically. But until that happens then agendas will keep getting in the way and it will be the disasters like the Panhandle (in this instance) that are the ones that show the willingness of human beings both before and after the event to be selfless and stay and look after others when they themselves are losing their own livelihoods at the hands of Mother Nature - but still prepared to look out for others more vulnerable than them despite all that. Their bravery and resilience is the most mind boggling - but in the best of ways
  11. Tamara

    Historic Category 4 Hurricane Michael

    They have now changed their minds once more... Shallower water, land interaction and diminishing chances of EWR are the flimsy straws to clutch in terms of (relative) damage limitation. But nothing will prevent what looks a very grim reality. Terrifying for those who decided to stay and who maybe thought they could ride out a Cat 2/3 based on previous experience. Hard to imagine the fear until you get a personal experience of something like this On an another media related note here in the UK, cannot comprehend how coverage by the BBC is next to non existent on this event. Plenty for Florence, and based on the much longer heads up, but this one appears to have gone right over their heads...
  12. Tamara

    ***Winter Countdown Thread 2018-2019***

    The September QBO data shows continued weakening progression of the easterly phase to -9.91 at 30 mb from -20.41 in August https://www.esrl.noaa.gov/psd/data/correlation/qbo.data The interest in terms of further QBO transition lies in the precise relationship, as defined by temperature differential, between the seasonally warming tropical stratosphere in the Southern Hemisphere in Spring and the developing polar stratospheric vortex at this opposite time of year in the Northern Hemisphere. This temperature differential relationship determines both the concentration and efficiency of transport of ozone through Brewer--Dobson circulation mechanism between the poles and which in turn will determine the relative strength or unstable weakness of the polar stratosphere heading into winter. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2013RG000448 Comparison given below here of upper stratospheric temperatures over the tropics between this time last year and where we are at in 2018. The relatively colder than the mean trends of the fall season last year set the scene for the less than hospitable environment with which the polar stratospheric vortex attempted to develop. This is because a relatively colder than average tropical stratosphere enhances BDC circulation of ozone to the NP and invites a warmer than average polar stratosphere. As everyone knows, a warmer and more unstable stratospheric profile is conducive to higher latitude blocking through inhibition of polar westerly gyre. Transitional QBO phases though, underline especially how the phase relationship is not black and white in terms of potential blocking outcomes because the timing and speed of transition phasing determines any window of opportunity for critical overlap period that often occurs during such a transition where residual -ve zonal winds c/o departing easterly QBO are flushed into the tropopause layers by the descending incoming +ve polar westerly wind anomalies. It is quite possible, and history shows us it happens, for blocking potential to actually be increased during this "precursor" phase change period assuming particularly if other background factors are also conducive to this (e.g solar activity and low frequency tropical convection forcing related to ENSO) (A converse +ve to -ve QBO phase switching of course holds the same opposite permutations correlation-wise). Taking all these relationships into account and how they may potentially overlap and interact, it makes any prediction tricky as one might expect. With the exact evolution of spatial ENSO anomalies in the Pacific still uncertain in terms of any Nino development - then in terms of looking for that blocking potential it is also important that the low frequency tropical convection signal (MJO) features an eastward progressing amplitude phase by or before November to help facilitate any of this overlap potential. A chicken and egg scenario in the sense that the departing -ve QBO phase is in itself augmentative to active tropical forcing when related to the present solar cycle - at the same time as providing the bedrock to buoyant atmospheric angular momentum trends that in themselves are a product of active tropical momentum transport c/o MJO activity. Active amplitude tropical convective cycling subsequently promotes the poleward transporting of +ve AAM anomalies to enhance rossby wave dispersion via mountain torque in the extra tropics and perturbs the tropopause layers - plus at the same time sustains westerly wind bursts across the Pacific that help propagate warmer sub water/SST spatial anomalies to assist development of an El Nino ocean base state. So notwithstanding all the uncertainties attached to them that add caution to trying to make definitive prediction - purely at least for purposes of adding to the general debate, all the various layers of factors discussed should prove interesting in how they interact and play out
  13. Tamara

    Teleconnections: A More Technical Discussion

    My own angle on analysis and benchmark for monitoring is highly symmetrical with this particular aspect of thinking and the importance attached to the differences. as stated. As I see it, when we are looking at the atmosphere/ocean relationship and trying to incorporate that (plus a variety of other drivers) into a geopotential height anomaly NWP framework pattern, whether that is shorter or longer term - the bread and butter starting consideration is the precise relationship that the atmosphere adopts to the ocean base state. In that sense, looking at the ENSO base state per se is not going to give any accurate foresight into NWP evolution beyond the usual broad-brush teleconnectic assumptions. Its not that these are not helpful - its just that it leads to some x+y assumptions which are nowhere near as linear as they may appear at face value. These principle key beliefs, plus a whole load more, are why I place so much faith in the Global Synoptic Dynamical Model (GSDM) as a starting point to my own study and curiosity into matching up weather patterns according to the balance, or budget of wind-flows in the global atmospheric circulation at a given time - which in turn can give such good clues and insight as to how weather patterns may evolve both in the shorter and longer terms. When I speak of wind-flows, largely this refers in simple English to the movements and velocity of the Jetstream. Tropospherically, within the tropics and extra tropical boundaries where momentum energy flux constantly interchanges to alter wind-flow according to angular momentum budgets, the Pacific is a large engine room of upstream and downstream control on circum-global weather patterns and why the relationship of the atmosphere to the complex changes that occur within the ENSO zones are such an important consideration. So enough background and good vibration appreciation of the concepts, how about some analysis consideration of some background to the here and now vs the possible way ahead: There is clearly no need for me, as part of my own assessment, to reproduce the data that the good folk so far have provided as part of the jigsaw on this subject. But to further investigate the GSDM atmospheric key responses provides what I believe is a very reliable barometer to the processes involved I was well aboard the Nino-esque low tropical frequency signal and +ve relative AAM anomaly gravy train during the latter part of the summer following the brief , but still significant, coupling of the atmosphere vs ocean that took place in late July. The periodicity (timeline recurrence) of low frequency tropical signalling had been consistently very buoyant right back to prior to the SSW that took place in February. This pattern had continued right into the summer - culminating in the eastward progression of that standing wave signal during July into the Pacific This drove both angular momentum tendency and total global atmospheric angular momentum into +ve territory, briefly - but still not replicating the spike attained during the very temporary reversal of the La Nina standing wave that was the culmination of the tropical>extra tropical momentum transport that 100% destabilised the stratospheric vortex in late winter. A retrospective plot of the The Global Wind Oscillation, which is a plot depiction of total global wind-flow in the atmospheric circulation and therefore a reflection of where AAM sits against parity,isn't currently avaialble by way of further illustration - but it laddered up into the El Nino attractor phases 5,6 and 7 in reflection of the strength of the momentum transport anomaly Below is a retrospective AAM anomaly chart courtesy of Victor Gensini maproom creation. This one year retrospective AAM anomaly plot advertises number 1: The long domination of the La Nina standing wave that had prevailed up to the SSW in February - as depicted by how much time has been spent with greater -ve or easterly trade wind domination at the expense of westerly wind additions added to the atmospheric circulation, and number 2: Just how much the atmosphere has still struggled to shake off the shackles of this Nina legacy since the SSW, despite the progression of the ENSO ocean base state to take on a more Nino-like spatial status, at least within the central Pacific Its this context, which I think illustrates that' its the atmospheric response in terms of how the tropics and extra tropics process easterly (or -ve momentum flux) and westerly (or +ve momentum flux), that determines the arrangements of the longwave hemispheric patterns - as also dictated (augmented or detracted) through natural seasonal wavelength changes. This being much more relevant and important in this respect in my opinion than the ENSO base state per se despite its changes away from a La Nina state in this time. ENSO base state relationships with the atmosphere can manifest themselves in a variety of ways from one matched up face value scenario to the next. Especially if we take other pernicious drivers like unstable sea ice patterns and associated superimposed warming forcing into account which further amplify and distort the synoptic patterns that occur as manifestations of those variable relationships. The days of the analogue and "one size fits all pattern match" is on stony ground. At least for those who attempt seasonal forecasts out there. This summer in 2018, despite the barometer reflection of the atmosphere lagging the ocean Nino progression with a stubborn Nina-like circulation the gradual warming profiles of the Pacific through repeated oceanic convectively coupled kelvin wave activity .... ...…...serving to move bodies of sub surface water eastwards and to the surface to increase the spatial extent of warming within the ENSO profile. I think this tweet from MV in late August summed up that situation Importantly though, the movement of the low frequency tropical signal though late July had already started coupling up and imprinted the atmosphere onto the newly developing El Nino standing wave. This might have appeared to represent a real coupled shift regime at last. Tentative and provisional as this move was, it was the first signal since the huge momentum processes leading up to the SSW that tha atmosphere finally wanted to go along with the shifting base state. Its been this (and admitted desire to see change out of a rut!) that had driven my own enthusiasm for a slow, but steady process towards a weak El Nino state during September and October and establishing more generally into the late part of this season and early winter. This summer seasonal momentum has not carried though however, much as previous analysis on this page has noted and by the AAM anomaly chart which, as illustrated above, has slipped back to previous generally -ve status. If we take a look at frictional torque tendency...… ……..then resumption of the Nina type signal of repeated easterly trade wind propagation has occurred since mid August around 20 to 30N which has created a -ve tendency to wind-flows and negated/supressed the Asian jet extensions in the extra tropics that are triggered by both low frequency tropical convection attempting to head into the Pacific, and the micro scale cyclonic activity as represented by the fledgling Nino standing wave trying to get implemented The persisting -ve South Pacific Oscillation largely responsible for this - meaning anomalous heights in the South Pacific with trade winds emanating north from the region and counter-acting the ENSO warming induced by westerly wind bursts c/o of CCKW, MJO and ACE related tropical activity. These countervailing trade bursts showing up on the Hovmollers wind anomaly plots as shaded blue close to the dateline Where the extra tropical westerly wind bursts are met by these tropical trade wind easterlies, then an eddy and amplification in the jet stream occurs. This is effectively the inflexion point of the -ve frictional torque response around 30N - with height anomalies propagating polewards from the tropics into the North Pacific and displacing atmospheric disturbances downstream over the US. Frictional torque responses lead mountain torque tendency responses, so the inverted pattern with greater easterly tendency present overall than westerly tendency results in a -ve Asian MT …… .......and the effect of falling frictional and mountain torque tendency impacts on relative and global atmospheric angular momentum and is reflected by the GWO back towards a low amplitude La Nina type Phase 1 signal Further downstream from the Pacific, the response of the deceleration of the jet in the Pacific is to also bolster sub tropical high pressure in the Atlantic c/o of both Bermuda and Azores ridges. The easterly trade winds emanating from the tropics help steer the developing tropical activity coming off the AEW with minimal wind shear to aid their development. Much as Florence and her family are more than amply demonstrating at present as everyone is aware. The tropics are very much engine of pattern change, and the periodicity of the MJO cycle points to the look out for a next amplitude cycle. AAM modelling, as mentioned, has been and still is persistently bullish about an upturn in AAM tendency relative to increased low frequency signal. Its this, that is required to redress the AAM budget within both the tropics and extra tropics to induce a more sustained and greater +ve frictional torque and extra tropical +ve momentum response as westerly winds change the budget of wind-flows (essentially re-configure the jet stream patterns from upstream). Converse to the processes within a -ve frictional lowering angular momentum signal, increased +ve westerly wind momentum gaining the upper hand results in an increased Asian jet extension, which serves to de-amplify the sub tropical high pressure in both the Pacific and then downstream in the Atlantic - and in the process change the greater balance of convectively coupled ocean>atmosphere cyclonic/hurricane activity back to the Equatorial Pacific The EPS VP200 convection anomaly depict a changing signal in the 15 day period, with some credence to greater westerly wind activity and in turn a cessation of the "destructive" Nina-like action on the ENSO zone - and with warming from the sub-surfaces replacing cooling. The AAM budgets and the GWO will ultimately provide for me the litmus test of how the atmosphere responds in reality away from model forecast suggestions The GWO response would be one of tracking away from the La Nina type Phase 1,2 and 3 orbit signature and a representation of +ve frictional torque increasing +EAMT into tendency above parity. Such an increase within the AAM wind-flow budget implies the GWO heading back to "transitional" precursor El Nino phase 4. However, this is only half the story for the extended period for those looking towards late season and on into winter. If the Nino standing wave is to recover assertion, let alone sustain, then the frequency of westerly wind bursts needs to sustain and the low frequency MJO signal provide the sort of eastward amplitude progression of late July to make this happen. Should this be insufficient, and there is no way of answering this at this time, then question marks will be raised at the particular ocean vs atmosphere status that will be in place at the same time as the stratospheric vortex is under-going its usual seasonal traditional rituals. This of course relating also to QBO +ve westerly phase descent as well as solar cycling all attendant with Brewer Dobson circulation of ozone transport from the tropical stratosphere in Southern Hemisphere Spring-Summer to the Northern Hemisphere opposite seasons.
  14. Looking forward to his thoughts on a range of topics that I know he already has great insight into. Not least this topic Edit..such timing!? That eyewall needs to be watched - while Florence may have dropped back a touch as part of the natural re-cycling, it could be the harbinger to even more intensity than seen before. And that is not sensationalist unfortunately. These stages are quite critical and a fine line between continued (apparent) struggling for longer or the worse scenario
  15. Yes it is a tad east- maybe 'sticking to its guns' was not quite the most accurate description - but its still a departure from the GFS and German model and close to the majority EC cluster this morning (including the operational). The point was meant to be that it has not adjusted as much as has been suggested it might and it seems to me to fit analysis as made earlier
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