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  • Gwo And Global Angular Momentum


    Message added by Paul

    Please be aware that these comments were copied here from another source and that the date and time shown for each comment may not be accurate.

    Glacier Point said:
    Where do you see the GWO going in the next few days Mark ? If it's back to phase 1-2, some support for Icelandic block, phases 3-4 and more of the Atlantic influence perhaps ?

    Ok I will start a new thread for dicussions along this line and perhaps I will draw on some ideas expressed in the stratospheric thread and artic sea ice thread. I guess you would be the best person to explain all this GP but for those who don't know this thread is about global angular momentum and how it oscialltes up and down (Global Wind Oscillation) along the lines discussed by Ed Berry.

    Angular momentum is of course a measure of the turning force in the winds, so could perhaps be considered a measure of the strength of low pressure systems, but also relates to how much the jetstream undulates and how much blocking we have.

    The budget of angular momentum goes up and down as energy is lost as weather systems crash into mountains and increases as cold air meets warm. Each phase of increasing and decreasing momentum suggests different types of weather for the UK. Looking at the current GWO plot we see a liklihood of going into phases 3 and 4 based on how it usually cycles round.

    This implies increasing angular momentum as the various torques including mountain torque diminish (i.e those things which take energy out are not active).

    This is certainly true of mountain torque.

    For frictional torque and gravity wave torque then the jury is out.

    Overall it looks like global angular momentum is on the increase.

    The tendecy during december has been upwards.

    Short term I think we are looking at phases 3-4 and more of an Atlantic influence. What I am guessing at though is that low pressure systems crossing the US will increase mountain torque, equally the jet stream across india is not a weak flabby one which might increase asian mountain torque. The strong jet in the western pacific along with OLR charts suggest strong trade winds with a stationary high to the north east of Australia and convectional activity to the north west of Australia. So back to phase 1-2 fairly quickly I think afterwards.

    All maps are available in the link below.

    PSD Map room for AAM

    I am sure GP will tell us what he expects from the MJO and convectional activity in the pacific and how and if he expects rossby wave development as a result. It is those Rossby waves which in part will affect the stratospheric vortex and the low angular momentum could be linked to a more blocked pattern and sea ice build up to our north which I talked about in associated threads.

    What we should always remember though that this a complex interaction of parts of which the stratosphere plays a large part during the winter.

    Please note that this post and subsequent comments have been copied from the forum, so the dates/times of the comments are not correct.

    Edited by Paul

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    Clearly some issues with the transference of negative wind anomalies across the upper part of the troposphere which make previous thoughts somewhat waide of the mark in relation to cold. However, the general circulation has progressed as anticipated. The extended range discussion is likely to continue to revolve around a strong reload of La Nina type pattern and when or if the impacts of a significant stratospheric warming will take effect.

    Latest thermal and zonal wind anomalies clearly show the effects of the warming event to have penetrated between 150 hPa and 200 hPa layer - i.e. across the tropopause.

    Further downwelling is taking place, although at a painfully slow rate. Crucially

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    Doh ! let's try again.

    Clearly some issues with the transference of negative wind anomalies across the upper part of the troposphere which make previous thoughts somewhat waide of the mark in relation to cold. However, the general circulation has progressed as anticipated. The extended range discussion is likely to continue to revolve around a strong reload of La Nina type pattern and when or if the impacts of a significant stratospheric warming will take effect.

    Latest thermal and zonal wind anomalies clearly show the effects of the warming event to have penetrated between 150 hPa and 200 hPa layer - i.e. across the tropopause.

    Further downwelling is taking place, although at a painfully slow rate. Crucially, the zonal winds across the polar region remain relatively light which should allow for the atmopshere to respond to tropical forcing although it is noted that polar vortex is attempting to reform towards eastern Siberia and the NW Pacific sectors which might be resisting so far the pressure from above. The impact of downwelling will I think still impact the surface although when remains a big question mark. The chances of a very blocked March and April have very much increased from my perspective (cold and wet spring?) through the timing and magnitude of the stratospheric event.

    A strong trade wind surge is ongoing in the tropics with anomalous 'Branstrator' mid latitude ridges now evident. Latest tropwave plots depict this surge in the central-western Pacific and also strong anticyclone developing over Equatorial Africa and the western Indian Ocean leading to convective surpression. OLR plots also show this nicely.

    This is signalling a general lowering in GLAAM. Also signalling this, a strong negative mountain torque has developed over Asia which, in tandem with falling frictional torque, is leading to a sharp decline in momentum over the mid latitudes and generally within the atmospheric framework.

    This falling tendency in momentum has driven the GWO through phase 3-2-1 (as anticipated) and resulted in a strong mean ridge in the Atlantic featuring within the likely weather for the medium term modelling. Further falls in momentum are likely and we are potentially looking at a high amplitude orbit through phases 1-2-3 within the next few weeks.

    http://www.cdc.noaa.gov/map/images/gcm/gwo_40d.gif

    Composites for thhese phases identify a mean ridge in the Atlantic and trough over Scandinavia as continuing responses.

    Whether or not the effects of the stratospheric warming detonate into the lower atmosphere during the outlook period is unclear. If they do, this will serve to 'excite' the pattern of ridges and troughs resulting in height rises over Greenland.

    For my money, we are likely to continue with the pattern of ridges and troughs that we see now, possibly with a hint that the last week of the month will start to to take effect;the impacts of the stratospheric warming with decreased momentum leading to a northward shift in the ridge with split flow. I have more confidence in more progressive blocking taking place during March. Organisers of the Cheltenham Festival (mid March), take note.

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    an idea of the time lag Stewart for it to show, say at 500mb?

    For a normal event John, 21-30 days should have been normal timlag. However, this is clearly not a normal event and it may well be that it will have a slower and much more sustained (inter-seasonal) impact on the circulation of the Northern Hemisphere throughout March and April.

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    Could someone tell me what "nbsp" stands for?

    And also "MMW", which is being used elsewhere relating to Strat. issues?

    Looks like a double whammy from this warming. Not helping Winter; Ruining Spring!

    Len

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    Could someone tell me what "nbsp" stands for?

    And also "MMW", which is being used elsewhere relating to Strat. issues?

    Looks like a double whammy from this warming. Not helping Winter; Ruining Spring!

    Len

    It's (nbsp) a typo Len - I was timed out on the edit and the recovery function inserted it.

    Major Mid Winter Warming = MMW

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    Doh ! let's try again.

    Clearly some issues with the transference of negative wind anomalies across the upper part of the troposphere which make previous thoughts somewhat waide of the mark in relation to cold. However, the general circulation has progressed as anticipated. The extended range discussion is likely to continue to revolve around a strong reload of La Nina type pattern and when or if the impacts of a significant stratospheric warming will take effect.

    Whether or not the effects of the stratospheric warming detonate into the lower atmosphere during the outlook period is unclear. If they do, this will serve to 'excite' the pattern of ridges and troughs ]resulting in height rises over Greenland.

    For my money, we are likely to continue with the pattern of ridges and troughs that we see now, possibly with a hint that the last week of the month will start to to take effect;the impacts of the stratospheric warming with decreased momentum leading to a northward shift in the ridge with split flow. I have more confidence in more progressive blocking taking place during March. Organisers of the Cheltenham Festival (mid March), take note.

    This statement has been typical of both you & john all Winter long & has lacked clarity for some of the regular posters on here ( the less seasoned ones shall we say)- you have both been touting this - through the GWO composites & John with the CPC model outlooks, however Height rises over Greenland cannot be compared with a true Greenland High-

    It would help if you would clarify what your expecting- As I would put the correlation with the Current Pattern & a Greenland High developing pretty close to Zero, however the height rises typically seen over Southern greenland with the transient ridges coming out of the atlantic are different & slightly more achievable, although just as unlikely at the moment to be sustained for more than one day especially with the GLAAM levels decreasing-

    For whatever reason the net effect thus far of the warming has been minimal, maybe more prevelant at 70n, but not at this lattitude- I suggest whatever propergates down now will not arrive with the big bang as some expected, but maybe having a weaker effect on the Westerlyness of the zonal wind-

    I did suggest on more than one occasion to John that the CPC charts were going to be wrong, but the secondary replies I gave to his responses must have been overlooked-

    Winter is Over- move on- get over it- the sustained cold never came ( surface stagnent surface air doesnt count)

    March may herald some more snow- but it not the same-

    Stewart- instead of posting the GWO composities of what we are seeing now ( & likely to be in the short term)- maybe post the 500mg Height anomalies for what your expecting day 7-10 or 10-15, at least thats a forecast then -

    S

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    It would help if you would clarify what your expecting- As I would put the correlation with the Current Pattern & a Greenland High developing pretty close to Zero, however the height rises typically seen over Southern greenland with the transient ridges coming out of the atlantic are different & slightly more achievable, although just as unlikely at the moment to be sustained for more than one day especially with the GLAAM levels decreasing-

    For whatever reason the net effect thus far of the warming has been minimal, maybe more prevelant at 70n, but not at this lattitude- I suggest whatever propergates down now will not arrive with the big bang as some expected, but maybe having a weaker effect on the Westerlyness of the zonal wind-

    S

    Morning Steve.

    Readers of this more technical domain do so under the understanding that the terms used maybe different, and this may from time to time spill over into MO thread. Reanalysis of the H5 field anomaly for the last 90 days shows a weak to moderate strength positive anomaly over Greenland and a stronger one centred in the Atlantic.

    This is different to you spell binding Greenland High yes, but see the caveat. Moreover, there has been two episodes this winter that have featured significantly greater positive anomalies - over Christmas into the New Year and 1st week February. The former was a good example of retrogression from Scandinavia. I would therefore maintain that references by myself and John have been correct and appropriate.

    Winter is Over- move on- get over it- the sustained cold never came ( surface stagnent surface air doesnt count)

    I'm interested in the application of the GWO as a long rang forecasting tool. I will be here during the Spring, Summer and Autumn hopefully adding positive contribution.

    Stewart- instead of posting the GWO composities of what we are seeing now ( & likely to be in the short term)- maybe post the 500mg Height anomalies for what your expecting day 7-10 or 10-15, at least thats a forecast then -

    Steve, read my thoughts on where I think the GWO is heading within the extended range - phase 1-2-3 orbits, probably remaining in a quasi-stationary orbit around phases 2/3 as the atmosphere plunges into deep negative momentum territory for March. The composites spell out what likely pattern (in terms of H5 anomalies) to expect.

    Updated mountain torques show a sharp decline over Asia in particular.

    http://www.cdc.noaa.gov/map/images/reanaly...ltaum.90day.gif

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    March may herald some more snow- but it not the same-

    In what way is it not the same?

    If you are talking about sustained snow cover then it is harder but other than that I find the comment slightly ridiculous. There have been some remarkable March snowfalls in the past.

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    It seems to me that Steve has been affected by the seasonal switch! I.e. once we approach the beginning of spring we should forget snow and cold, and seek warm sunshine.

    Last year, we received the best snowfall in March and April, so that in itself makes it worthwhile to continue to look for wintry weather in the models.

    As for snow that lasts for days or weeks, well that's unusual in lowland Britain at any time of the year, yet this year we achieved it despite not particularly 'favourable synoptics!

    Karyo

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    Only just noticed the post from Steve and the comments from GP (Stewart)

    First let me say I've never done any other than repeatedly, if anyone reads my lrf outputs, said anything other than its a new area to me. I find it fascinating trying to give a general idea for 2-3 weeks ahead. Like GP I'll be here Steve, through the whole year, God willing, to carry on, as I did through the whole of last year Not just Winter, trying to improve the lrf idea, trying to learn more about the topic.

    I thought I had said enough times that no single link is the way to forecast, you have to look at every item that may impact over the time scale you are trying to forecast for. That is what I try to do. I try not to be selective. I try to post things as I see them honestly and I'm pretty sure my lrf's over the past 13 months show that. I continue to believe that, be they CPC charts, ECMWF hemisphere charts, Stratosphere input, ENSO etc etc, all have a part to play and all of us, I hope, accept that we are learning. No one gets it right and I've already put my hand up regarding the prediction of deep cold by now. I have been forecasting for far too long to be afraid to say I got it wrong.

    All of us have something to contribute to this forum so lets just do that and not, as winter (officially) draws to a close get a bit niggly with one another.

    As, I think most of you would find, if you apply the Mr D winter index for the station nearest you, many of us have had a fairly memorable winter in terms of length of cold, some even for extremes of cold, and some for length of snow on the ground.

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    It seems to me that Steve has been affected by the seasonal switch! I.e. once we approach the beginning of spring we should forget snow and cold, and seek warm sunshine.

    Last year, we received the best snowfall in March and April, so that in itself makes it worthwhile to continue to look for wintry weather in the models.

    As for snow that lasts for days or weeks, well that's unusual in lowland Britain at any time of the year, yet this year we achieved it despite not particularly 'favourable synoptics!

    Karyo

    Amen to that :D

    Don't want to derail this very good thread, there are too many threads open at the moment lamenting something that shouldn't be lamented. The factors that are being monitored on this thread, and in conjunction with the strat thread are still very much there. Even if there continues to be a stalemate in the models atm. I am very interested in how the start to the coming Spring plays out. I can see a very easterly and northerly dominated one with all the interest that that entails for our part of the world.

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    Current Analysi of the stratosphere.

    5 Days out.

    From this I would take a strong signal for blocking in the northern Pacific and a secondary weaker signal for blocking in the north Atlantic. This kind of shows up on the GFS blocking maps.

    8 DAYS OUT

    How does it compare to ECM and GFS forecasts.

    Clearly the strong signal is across the other side of the world and we are more likely to be influenced by GWO and as a downstream product of the strong signal in the pacific.

    GWO is now headed strongly into phase 1 and there are clear indications that Global Angular momentum is likely to tank. I see this as an indication that we are never going to be far away from being north of the jet stream, but indications are that we might just miss out on the really cold stuff. Spring weather with a misture of cold and mild seems in order.

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    I must admit to not understanding fully the implications of all the different teleconnections and how they interlink with one another. I'm sure i have read in past posts how a rising glamm is good for blocking then next i read that a sinking glamm is what you need,so at times very confusing.

    Last winter the glamm went through the floor and we all know how that turned out, although whether that was from the glamm or cold stratosphere and strong vortex i don't know.

    Could someone explain what the GWO is in relation to the glamm, mountain torque and friction torque, i think thats the lot.

    I was under the impression you needed angular momentum to mix with the polar westerlies which would disrupt the zonal westerlies adding warming and blocking at higher latitudes.

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    I must admit to not understanding fully the implications of all the different teleconnections and how they interlink with one another. I'm sure i have read in past posts how a rising glamm is good for blocking then next i read that a sinking glamm is what you need,so at times very confusing.

    Last winter the glamm went through the floor and we all know how that turned out, although whether that was from the glamm or cold stratosphere and strong vortex i don't know.

    Could someone explain what the GWO is in relation to the glamm, mountain torque and friction torque, i think thats the lot.

    I was under the impression you needed angular momentum to mix with the polar westerlies which would disrupt the zonal westerlies adding warming and blocking at higher latitudes.

    Generally, rising GLAAM is better for promoting a disrupted flow pattern which is supportive of higher latitude blocking. That's why blocking is more prevelant during El Ninos (+GLAAM) rather than La Ninas (-GLAAM) during the winter time and this is related to the location of tropical forcing and momentum budgets.

    However, this is seasonally dependent. As we move into boreal spring and summer, blocking is more favoured during low angular momentum due to seasonal wavelength changes. That's why the last few summers have been rank. Low angular momentum regime has dominated (and still does). If you are after your traditional winter cold and summer warmth, an El Nino and +GLAAM regime is for you.

    There is one further (and confusing) anomaly. Falling angular momentum (meaning that the GWO is attracted towards phases 1 and 2) can lock in place the existing pattern during the second half of the winter. The best example of this is February 1963 where the GWO spent most of its time in the low momentum phase 2 at high amplitude.

    Although we didn't come very close to this happening this year, it did at one stage in late jan / early Feb look plausible. But then we picked up some momentum and moved to phase 3 where we stayed for some time.

    Torques make up significant parts of the momentum budget. They are large drivers in tendency in angular momentum helping to remove or add winds to the atmosphere. They occur as a result of pressure differentials across mountain ranges or longitudinal air masses. Think of the jet stream as a type of frictional torque by which winds are added or removed.

    The complex interactions of these torques is best monitored on a daily basis to see how falling and rising torques (they usually go up and down in sequence) can impact on overall tendency of angular momentum and the GWO.

    Right now we have falling mountain torque which is driving the overall level of GLAAM downwards once more. Easterly winds are being added to the extratropical atmosphere (and some evidence of lack of westerly motion across the tropics).

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    Very much appreciated GP thanks.

    So would i be right in saying that roughly speaking the GWO is a measure of glamm, mountain torque, and frictional torque combined.

    .. and all of these factors listed at the PSD Map Room:

    http://www.cdc.noaa.gov/map/clim/aam.90day.total.shtml

    Torques are by the largest extratopical influences with tropical convection (MJO component) also included within these monitoring products.

    The best indicators as to where the GWO will be located are tendency in angular momentum which gives an indication in the rate of change of the GWO (how fast and which way the GWO orbits):

    http://www.cdc.noaa.gov/map/images/reanaly...d.sig.90day.gif

    and the overall level of angular momentum:

    http://www.cdc.noaa.gov/map/images/aam/glaam.gif

    which gives us our magnitude of the GWO. Note that the MJO component (the tropics is becoming very quiet) as convective supression in the west Indian Ocean takes effect and strong easterly trade wind push in the central Pacific:-

    http://www.bom.gov.au/bmrc/clfor/cfstaff/m...Last40days.html

    As can be seen, both suggest a negative tendency high amplitude orbit. Currently in phase 1:

    http://www.cdc.noaa.gov/map/images/gcm/gwo_40d.gif

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    Just time for a very brief update.

    Key thing, strong upper tropospheric anticyclones have become established across east Africa extending into the western Pacific.

    http://www.bom.gov.au/bmrc/clfor/cfstaff/m...m/OLR/m.3d.html

    This is indicative of the tropics becoming strongly supressed. A lack of topical forcing is very significant as this is a major driver in global momentum. Westerly motion in the atmosphere has dropped rapidly. Look at how the MJO has become non existent:

    http://www.bom.gov.au/bmrc/clfor/cfstaff/m...Last40days.html

    Mountain torques are responding to this with negative torques developing once again:

    http://www.cdc.noaa.gov/map/images/reanaly...ltaum.90day.gif

    This is driving a strong negative tendency in the GWO which, as per last posting, as stalled in phase 2:

    http://www.cdc.noaa.gov/map/images/gcm/gwo_40d.gif

    The synoptic response thus far is as anticipated: mean Atlantic ridge; Scandinavian trough. Moving forwards, March signals a changing wavelength (as January is different to February or December). Composite reanalysis for GWO phase 2 signals a shift in the mean ridge further west edging the Scandinavian trough westwards towards the UK with the jet orientated NW-SE (and south of the UK). As time progresses, the trend should be for height rises over Greenland which also accords with the impacts of the MMW.

    As Ed Berry notes, the effects of the MMW continue to be manifested in weather patterns - the storm track being shifted anomalously southwards against the climatological trend. I've read some views recently questioning the impacts of the MMW. True, the deep cold expected by this quarter has not materialised, yet. However, study of the anomalous warmth of the upper troposphere and lower stratosphere tells us that the impacts of the stratospheric warming have not gone away. Far from it. They continue to represent a serious inter-seasonal weather issue which will continue to influence our weather patterns for the next 4-6 weeks. Make no mistake, I think there is a serious amount, a shed load, of blocking upcoming in March and early April although this is tempered slightly that this seemed likley for February but has yet to materialise.

    http://www.cpc.ncep.noaa.gov/products/stra...JFM_NH_2009.gif

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    The synoptic response thus far is as anticipated: mean Atlantic ridge; Scandinavian trough. Moving forwards, March signals a changing wavelength (as January is different to February or December). Composite reanalysis for GWO phase 2 signals a shift in the mean ridge further west edging the Scandinavian trough westwards towards the UK with the jet orientated NW-SE (and south of the UK). As time progresses, the trend should be for height rises over Greenland which also accords with the impacts of the MMW.

    ... this brings us nicely to where we find ourselves now and what is likely in the next 10 days. Yet another case of using the GWO framework to give forecasters a distinct edge within long range timescales.

    Looking further ahead mid March onwards, the GWO story will be dominated by a continued low angular momentum base state.

    OLR plots show localised levels of anomalous and largely unorganised convective activity around the west Pacific and Indonesia. There are also large anticyclones occupying large parts of Africa, the Indian Ocean and sub-Continent, central Pacific.

    http://www.bom.gov.au/bmrc/clfor/cfstaff/m...m/OLR/m.3d.html

    This means that one of the engines driving forward (west) motion in the atmosphere is spluttering. The MJO is a good guide to this and it currently is very weak in the locale of the far east Indian Ocean:

    http://www.bom.gov.au/bmrc/clfor/cfstaff/m...Last40days.html

    Easterly trade winds still persist across large parts of the Pacific and Atlantic and any MJO activity is likely to be suppressed.

    Since the last posting, the GWO has shifted in high amplitude phase 3/4:

    http://www.cdc.noaa.gov/map/images/gcm/gwo_40d.gif

    This is a result of complex atmospheric processes adding westerly motion to the extratropical atmospheres, principally frictional and some mountain torques shifting westerlies poleward:

    http://www.cdc.noaa.gov/map/images/reanaly...ltauf.90day.gif

    http://www.cdc.noaa.gov/map/images/reanaly...ltaum.90day.gif

    Note the development of positive frictional torque at 45N however which is indicative of the jetstream being shifted southwards.

    Overall levels of global angular momentum, in excess of -1.5 Hadleys reflective of the La Nina base state:

    http://www.cdc.noaa.gov/map/images/reanaly...m.sig.90day.gif

    The lack of tropical convection and natural processes which oppose westerly wind additions will reverse this most recent spike in tendency in angular momentum:

    http://www.cdc.noaa.gov/map/images/reanaly...d.sig.90day.gif

    I suspect a GWO orbit along the lines of phases 4-3-2-1 1-2-3 (quasi-stationary 2/3) will occur. Composite reanalysis for medium amplitude phases 2 and 3 look like this:

    Remember these are H500 field anomalies - not absolute values - but the inference is as follows:

    1) disrupted Atlantic longwave pattern with continued tendency for cut off lows to develop in the north- western Atlantic sector;

    2) unsettled;

    3) winds from a northerly, north westerly, north-easterly and easterly vectors.

    Therefore the outlook continues to remain below average.

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    It sounds like winter may not be over yet then. The models seem to be picking these signals up quite well with a very very promising looking ECM run this morning of something alot colder and more wintry.

    How long do you see this signal for a southerly displaced jet to last GP.

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    Stewart a question

    we all know what did not happen with the Stratosphere warming. The fact that at 30mb, its almost back to normal?

    Is there any link with this and what you are reporting and now forecasting in your view?

    If so what is your view on why we got no real effect, well most of the northern hemisphere got no real effect from this huge warming event?

    answers in simple English please, none of your exotic science if possible for me as a simple soul!

    many thanks

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    Before we can qualify what if any impacts the MMW has had, we must I think contextualise this event within a west QBO under low solar minima. There has never been an early breakdown of the polar vortex during such conditions and we can see this I think with the polar vortex remaining intact or attempting to reform.

    There have I think been several impacts of this warming:

    1) angular momentum at the upper levels has dropped since mid January. This can be seen in angular momentum plots:

    http://www.cdc.noaa.gov/map/images/reanaly...g.qbo.90day.gif

    2) the Artic Oscillation has shown 2 large negative phases over February. Nothing special in that unless you consider the west QBO / solar minima. I speculate that had this been an east QBO, the AO would have come up with a value in excess of -4 SD.

    http://www.cpc.ncep.noaa.gov/products/prec...ex/ao.sprd2.gif

    note the third drop coming up.

    3) the storm track across the NH has been shifted anomalously southwards. The largest positive zonal wind anomalies for February are evident across North Africa.

    So whilst the spectacular blocking synoptics have yet to materialise, the MMW has resulted in measurable impacts across the NH, perhaps more diffuse but non the less significant. These continue as the anomalously warm lower stratosphere persists.

    http://www.cpc.ncep.noaa.gov/products/stra...JFM_NH_2009.gif

    Bar far the most discernible impact from the MMW for me is its reinforcement of a low angular (Nina like) base state. That relates directly to my expectations for the next few weeks. Low angular momentum, phase 2/3 of the GWO = blocking during March when shortening wavelengths allow for the release of colder air, even within the context of the west QBO.

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    thanks Stewart

    I think!

    Taking your points 1), 2) and 3).

    If I summed it up thus for numpty's like me would my overall idea be correct?

    Low GWO means that northern blocking in winter is more likely than an active Atlantic?

    and this in spite of the QBO having a westerly component?

    but with a low solar minimum?

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    thanks Stewart

    I think!

    Taking your points 1), 2) and 3).

    If I summed it up thus for numpty's like me would my overall idea be correct?

    Low GWO means that northern blocking in winter is more likely than an active Atlantic?

    and this in spite of the QBO having a westerly component?

    but with a low solar minimum?

    Low angular momentum during the winter makes blocking less likely at high latitude and the overall flow pattern zonal (there are exceptions in terms of specific months and GWO phases).

    Both this and the west QBO emphasise to me how well we have faired, all things considered. The factors that have been on our side have been the solar minima which has beefed up the polar cell and the hemispheric arrangement of SSTAs.

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    My take would be that Low angular momentum means less energy going into the jet stream. This would suggest to me that during a low angular momentum period the jet stream tends to stay south and not arch northwards leading to high latitude anticyclones. This means that low angular momentum is not good for a particular type of blocking. Typically we get cold periods due to being north of the jetstream, but the Atlantic storm track is rarely disrupted.

    A strong la nina period which is associated with low angular momentum however means trade winds tend to be strong across the Pacific. This leads to a stationary anticyclone north of the equator which by nature of the fact it does not move can cause extra tropical blocking to its north. Unfortunately this type of blocked pattern is not often conducive to cold weather in the UK with I think high pressure in the north pacific, low pressure in north west Canada and high pressure again in north east Canada. All this does depend on the season and number of Rossby waves around the globe, hence why Glacier Point uses re- analysis to show the effect during any particular month.

    You might think that a strong el nino period would give you the opposite effect, but what you get is a strong jet blasting across the Atlantic with the UK ending up with a largely wet winter. You will get periods where the jet arches northwards but any anticyclone tends to get undercut or blown away by the strong jet. In contrast to the fixed anticyclone north of the equator in the Pacific you tend to get Thunderstorm activity (MJO) moving west to east across the equator, again not giving a very fixed pattern.

    The point about the QBO and its direction is that stratospheric anomalies tend to be transmitted down to the troposphere during a easterly QBO rather more than a westerly one. This is not well explained why in literature but seems to reflect the fact that north pole stratospheric winds (stratospheric vortex) may be pulling in the opposite direction to equatorial stratospheric winds (QBO). I also think the actual nature of the Stratospheric disturbance plays a part. Split vortexes tend to lead to a lot of blocking, displace vortexes lead to less blocking and completely disrupted vortexes give very little blocking, but tend to reinforce low angular momentum. We have actually gone through all three of these phases with different results.

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    Yes thanks to both GP anb BF.

    This explains very well why (apart from the initial split) the MMW has not led to the blocking some of us would have preferred. The low angular momentum (perhaps from a more diffuse downwelling of stratospheric negative wind anomalies due to the persistant westerly QBO) coinciding with a weak La Nina state have contrived to prevent northern blocking patterns that every mid range forecast even seemed to suggest.

    This to me makes perfect sense with what we have seen on the ground and is another illustration of why we need all the troposheric fastors to be favourable to achieve maximum benefit from a SSW.

    c

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    One of the key things about Spring and Early summer is that the jet stream begins to shift North. Typically in the region of the UK there is a northern arm and a southern arm to the jet and where ever they occur you often get wet and windy weather. Due to the low global angular momentum (la nina like) state of the climate then the jet stream is currently further south than it would normally be. This is born out by the ITCZ being relatively far south across Africa for this time of year.

    I tend to think that we get two periods of about a month of wet weather as the jet stream moves north. During la nina those months might be April and June with August and October being wet as the jet comes back south. During el nino those months may be earlier for instance March and April. Ideally you would want a transition from la nina to el nino during spring which would push the jet north quickly, limiting the about of wet weather.

    One of the best teams for predicting la nina and el nino are the Australians who tend to look at the SOI (Southern Ocean Oscillation Index) as a pre cursor to the state of equatorial water temperatures in the Pacific (which is what la nina and el nino are). During the last month we have seen a significant change and although this was enhanced by some strong activity through phase eight of the MJO it should be noted that the recently dominate pacific trade winds have been over come.

    I will take time for the MJO signal to travel around the world again and to some extent you might expect some change at this time of year, but I still see some significance that may not yet be reflected in the models.Warm water volumes should be declining somewhat now so a full on el nino seems unlikely but the changes seem to be significant even though global angular momentum is on the low side.

    Since the stratospheric vortex has never really recovered from the mid winter disruption we have had an unusually spring like late winter season with very little pattern blocking. Significantly the North Atlantic storm channel has been open for over a month and this has had an impact on ice formation to our north especially in the Barents sea area (yes I do know all the caveats surrounding the following chart but it goves an indicator).

    This is perhaps not good news for snow lovers for next winter in the UK although the snow fields of Asia may still be quite late clearing leaving us watching for a beast from the east as a source of cold next winter. Coming back to the storm channel being open and how weather patterns seem to be to be limited to a two month period then the current pattern should not have that much more to run. I put this down to the rossby wave lengths (number of undulations of the jetstream around the world) tending to change with time and season.

    In conclusion I am quite hopeful for a drier spring season than usual with temperatures beginning to catch with the norm from here on in. I am also rather hopeful that with plenty of cold air to the north due to the low angular momentum conditions and with the jetstream beginning to come north more quickly we may have an interesting storm season ahead (although it may be shorter than usual?). We might also see a Hot month mid summer instead of barely escaping the clutches of the jet stream last year. I reserve the right to completely change my mind though if the SOI changes, or the stratospheric vortex reforms, or any one of a number of variables change.

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    Thanks for the interesting update BF.

    I don't know how this may affect things, but I reckon that the stratospheric vortex has more than reformed since the severe disruption in January. Looking at the mean zonal winds we are now running above average for this time of year throughout the whole height of the stratosphere. Does have any bearing on your thoughts?

    post-4523-1238656682_thumb.png

    post-4523-1238656695_thumb.png

    c

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