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Stratosphere watch 2018/19

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Comments

  • Registered Users Posts: 1,985 ✭✭✭BLIZZARD7


    ' The strat. vortex is currently weaker than all other years in the ERA interim record!!!
    The zonal mean zonal wind at 10 hPa 60N is today (GFS analysis): -8.6 m/s
    Weakest zonal wind at 10 hPa 60N in ERA interim record for todays date is: -8.4 m/s 2004
    Strongest zonal wind at 10 hPa 60N in ERA interim record for todays date is: 66.8 m/s 2009 '

    u10serie.png


  • Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    There is still no sign of downwelling of note over the next 10 days. What we've seen now in terms of wind reversals in the strat and movement down to upper tropospheric levels (200 hPa and below) is about the extent of what we will see in the foreseeable. There are no indications of any trend towards a more retrogressive (blocking) largescale pattern, the 50 hPa ridging at 150W from about 6 days not showing any signs of amplifying and cutting off over the pole by day 10. From 100 hPa downwards the patter remains remarkably consistent, with a low over NE Canada/Greenland and a zonal pattern over the Atlantic showing up right down to 500 hPa.

    For blocking towards the end of the month and into February we need to be seeing signs of reversals first at 100 hPa, then at 200, 300 and finally 500 hPa levels, but they are absent.

    GFS 100 hPa Analysis, 5-day 10-day forecasts
    470229.png

    470230.png

    470231.png

    ECMWF 100 hPa 10-day forecast
    470232.gif

    Seasonal zonal wind evolution and NASA 10-day forecasts
    45800508295_916d245e95_z.jpg
    45991019364_2c74c94d35_z.jpg
    45991025604_dd089dea64_z.jpg


  • Registered Users Posts: 2,150 ✭✭✭PukkaStukka


    Reading the posts above, are we heading for an anticlimax in terms of a proper wintry outbreak?


  • Registered Users Posts: 23,716 ✭✭✭✭Larbre34


    Reading the posts above, are we heading for an anticlimax in terms of a proper wintry outbreak?

    Far too early to say. SSW and PV are only possible factors to delivering a cold spell.


  • Registered Users Posts: 1,591 ✭✭✭gabeeg


    There is still no sign of downwelling of note over the next 10 days. What we've seen now in terms of wind reversals in the strat and movement down to upper tropospheric levels (200 hPa and below) is about the extent of what we will see in the foreseeable. There are no indications of any trend towards a more retrogressive (blocking) largescale pattern, the 50 hPa ridging at 150W from about 6 days not showing any signs of amplifying and cutting off over the pole by day 10. From 100 hPa downwards the patter remains remarkably consistent, with a low over NE Canada/Greenland and a zonal pattern over the Atlantic showing up right down to 500 hPa.

    For blocking towards the end of the month and into February we need to be seeing signs of reversals first at 100 hPa, then at 200, 300 and finally 500 hPa levels, but they are absent.

    This excellent analysis yesterday really knocked my confidence in the any upcoming potential.
    But I was buoyed again this morning with an excellent ECM run, and I read that we're finally starting to see some signs of reversal at 100 hPa.

    I've no idea how to verify that, so I'd love if you could please take the time to check for me. Ta


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  • Registered Users Posts: 358 ✭✭YanSno


    Zonal winds at 100hpa in postive, a certain deceleration but expected to stay well into positive.

    AVo8Srr.jpg


  • Registered Users Posts: 1,591 ✭✭✭gabeeg




  • Registered Users Posts: 13,477 ✭✭✭✭sryanbruen




  • Registered Users Posts: 13,477 ✭✭✭✭sryanbruen




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  • Registered Users Posts: 17,797 ✭✭✭✭hatrickpatrick


    sryanbruen wrote: »

    @Sryan, one area of stratospheric forecasting I'm still entirely ignorant on is what is meant by wave 1, wave 2, wave breaking etc when people discuss these forecasts. Without wanting to hijack the thread (I'll look up proper lessons on this after winter is over and the Night Walkers have been defeated), you and several others have mentioned previously that we may not see blocking results from this SSW event because unlike the Feb 2018 event, this one has been severely lacking in wave-2 activity.

    Is this still your assessment, despite various signs that downwelling is occurring? Is the lack of wave-2 activity still a problem as we head into next phase of Winter? Someone on Twitter mentioned that there's been a wave 2 "pulse" in recent weeks, but will this be sustained enough to change the pattern?

    Unfortunately this is an area I've tried repeatedly to get my head around and failed, so for the time being I must rely on your and others' expertise to interpret this aspect of the event :D


  • Registered Users Posts: 13,477 ✭✭✭✭sryanbruen


    @Sryan, one area of stratospheric forecasting I'm still entirely ignorant on is what is meant by wave 1, wave 2, wave breaking etc when people discuss these forecasts. Without wanting to hijack the thread (I'll look up proper lessons on this after winter is over and the Night Walkers have been defeated), you and several others have mentioned previously that we may not see blocking results from this SSW event because unlike the Feb 2018 event, this one has been severely lacking in wave-2 activity.

    Is this still your assessment, despite various signs that downwelling is occurring? Is the lack of wave-2 activity still a problem as we head into next phase of Winter? Someone on Twitter mentioned that there's been a wave 2 "pulse" in recent weeks, but will this be sustained enough to change the pattern?

    Unfortunately this is an area I've tried repeatedly to get my head around and failed, so for the time being I must rely on your and others' expertise to interpret this aspect of the event :D

    Well to explain this question, I must start from the bottom on the basis of what is a sudden stratospheric warming.

    A sudden stratospheric warming is a dynamic event that occurs in the stratosphere with a sudden rise of tens of kelvins in temperature. These warming events are the result of natural weather patterns and large-scale pressure systems like the Alaskan High producing atmospheric waves called Rossby waves (also known as planetary waves). These waves are propagated or travel upward into the stratosphere and often result in displacing the Polar Vortex away from the North Pole, along with a deceleration in the zonal winds. If continuous disturbance occurs via higher amplitude of atmospheric waves, further warming may take place.

    Meanwhile,

    Wavenumbers are defined by the number of troughs and ridges in a wavelength which stretches in a full circle at a given latitude around earth. They're usually identified on maps like 500mb geopotential heights. The different wavenumbers vary on the number of troughs and ridges along with amplitude of the waves.

    I, myself, is still learning on the matters of wavenumbers and only have a very amateur understanding of them. However, you will find some great resources online here and there on this matter. Just make sure you search for the correct thing like rossby or planetary waves, zonal wavenumbers etc.

    Thank you for the compliments but I would not put myself in the same league as GL, Cohen, Simon Lee, Butler etc.


  • Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    As sryan has said, wave-1 and 2 refer to the zonal wavenumber (number of tropospheric planetary waves present along a line of latitude). Wave 1 means one very large wave extending right around the globe, so on a long timescale. Wave 2 is obviously two waves, so of smaller scales in space and time. Wave 2 can be superimposed on wave 1, the same way the FM signal is superimposed on the carrier signal frequency. Then there are higher wavenumbers, referring to smaller and smaller disturbances, but the effects of these are less pronounced. The further north you go (higher latitude), the smaller the latitude circumference is, so the smaller a wave needs to be to a certain wavenumber compared to if it were further south (larger latitude circumference, see below).

    470762.png

    For each wavenumber there is a critical zonal windspeed, above which the wave can not propagate vertically ("break") into the middle atmosphere (stratosphere and mesosphere). When we have a low-wavenumber stationary wave (say wave-1), a moderate westerly wind below the critical speed (and fairly consistent with height) can allow upward breaking of the wave into the stratosphere, where it will disrupt the polar night jet (the strong westerly jet way up in the stratosphere). When this happens, adiabatic heating occurs due to subsidence of the air.

    I like to think of it all like having a bucket of water and stirring it vigourously anticlockwise (anticyclonically) with a stick to form an even vortex. Looking down from above, this mimics looking down on the northern hemisphere, the north Pole in the centre. The lowest level of water in the centre represents the lowest geopotential height of the cold polar night (polar vortex) sitting over the Pole. The outer edge of liquid near the bucket wall is the westerly polar night jet at lower latitudes.

    Now if you stick a paddle down into the vortex, it will disrupt the flow of water, just like an upward-propagating tropospheric wave disrupts the polar night jet. You can imagine how the vortex of water will now split towards the centre (Pole), and the whole spin of water will slow down. This is like the polar vortex slowing down and even reversing, causing the sudden stratospheric warming.

    If you quickly start the water spinning again then the disruption will be minimised and the effects will not propagate down to the bottom of the bucket. Likewise, the effects of the polar vortex split propagate downwards into the troposhere, but a lot of factors determine if and how much this happens. In this case the vertical wind profile has not really played ball to allow it to properly happen, and the vortex has already recovered up in the mesosphere and upper stratosphere, eventually extending down through the whole layer in the next few days.

    If you want to get your teeth into more theory then Holton's book is the best out there. I spent €90 on the hardback edition several years ago, but now it's available for free as a pdf below. :rolleyes:

    http://danida.vnu.edu.vn/cpis/files/Books/An%20Introduction%20to%20Dynamic%20Meteorology%20-JAMES%20R.%20HOLTON-%204th%20Edition.pdf


  • Registered Users Posts: 15,944 ✭✭✭✭Villain


    Finally some impact coming our way??

    https://twitter.com/MattHugo81/status/1087983706114064384


  • Registered Users Posts: 15,944 ✭✭✭✭Villain




  • Registered Users Posts: 13,477 ✭✭✭✭sryanbruen




  • Registered Users Posts: 16,550 ✭✭✭✭nacho libre


    I read an interesting post on Netweather that suggested there was not a split of the vortex due to a technical sww, but rather a severe wave 1 displacement event, this was the reason a piece of vortex ended up in the wrong place to bring about a beast from east.
    It does not seem a convincing explanation to me, as most experts agreed there was a technical sww which led to a split vortex. It just seems like it was one of those ssw that did not work in our favour

    It will be interesting to see what the experts learn ftrom this one.


  • Registered Users Posts: 8,219 ✭✭✭Gaoth Laidir


    I read an interesting post on Netweather that suggested there was not a split of the vortex due to a technical sww, but rather a severe wave 1 displacement event, this was the reason a piece of vortex ended up in the wrong place to bring about a beast from east.
    It does not seem a convincing explanation to me, as most experts agreed there was a technical sww which led to a split vortex. It just seems like it was one of those ssw that did not work in our favour

    It will be interesting to see what the experts learn ftrom this one.

    The amount of straw-clutching that has gone on with this event is amazing, so you're right, it's not a convincing argument and just looks like someone just trying to justify the many bust forecasts. If there was this wave-1 fly in the ointment, why wasn't it identified a few weeks ago? I've said all along, this one looked like being a SSW of little effect because there was never any indication of any major downward propagation, despite what many were trying to convince themselves of.

    But it's given many twitter accounts some added traffic, so in the end that's what it's all about, isn't it?


  • Registered Users Posts: 13,477 ✭✭✭✭sryanbruen


    Very strong Polar Vortex currently reaching record high mean zonal mean winds at 60N 10hPa.

    This is forecasted to not last long though with more normal mean zonal mean winds returning in about a week or so according to the GEFS. The final warming should be coming in 3-4 weeks or slightly more with the Polar Vortex going into hibernation for another Summer before we go on the rollercoaster again come Autumn.

    https://twitter.com/DrAHButler/status/1105875476294201344

    https://twitter.com/mikarantane/status/1104807136163450887


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  • Registered Users Posts: 13,477 ✭✭✭✭sryanbruen


    Latest forecast from the GFS shows the Polar Vortex remaining well organised into the second week of April with strong zonal mean zonal winds.

    Ln8Wf5D.png

    Similar with the ECM.

    0BrMdb6.gif


  • Registered Users Posts: 13,477 ✭✭✭✭sryanbruen




  • Registered Users Posts: 16,550 ✭✭✭✭nacho libre


    Well, a couple of falsehoods about what the Stratosphere would not be able to do after the stratospheric warming were put to bed this past Winter


  • Registered Users Posts: 13,477 ✭✭✭✭sryanbruen


    New study showing more types of SSW events than the classic two types with split-split, displacement-split and displacement-displacement events based on their wave amplitude.

    Currently not open accessible.

    https://twitter.com/AMSMiddleAtmos/status/1118896754160746497

    https://journals.ametsoc.org/doi/10.1175/JCLI-D-18-0223.1#.XLiVZBMbciE.twitter


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