Jetstream Question

Discussion in 'Alpine & Snow' started by BrentC, May 6, 2006.

  1. BrentC

    BrentC Hard Yards

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    I asked this in the "2006 weather quetion thread" with no luck - so I'll try again!

    I have a general question regarding what is the Jet stream.
    I have very little understanding of what it has to do with the weather (and snow). I know its just a current of fast moving air between warm/cold air masses. My question is - is there an ideal placement of the Jetstream for cold/snowy weather?
    I would guess that becuase it represents a boundry between the cold polar air and temperate air masses, then the further north the stream are locateed the better - because we'd have the polar air over southern Australia. Probably wrong though.
    Also - what happens when the two jetstreams overlap? Is this good?
    Cheers!
     
  2. BrentC

    BrentC Hard Yards

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    Bump Bumpety :woohoo:
     
  3. Falls expat

    Falls expat One of Us

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    Ok I will have a brief go at this.

    Jet streams develop in regions of strong thermal gradient.

    There are two main Jet streams of interest. The Subtropical Jet and the Polar Jet.

    The Subtropical jet meanders around about the 20-40 deg latitude region around the globe. The Polar Jet tends to hover in the 40-60 deg latitude band. However, there can be extremes outside these bands.

    The polar jet is located at the main boundary between cold polar air and warmer subtropical air.

    The Subtropical Jet is usually found a bit higher up in the atmosphere and is found in the tropical air and subtropical air boundary.

    As a general rule if the Polar jet buckles up towards SE Australia it will produce snow bearing weather. However, if Polar Jet peaks in its northward track say over the Bight then this is likely to drag warmer air from central Australia over the Alps. If it peaks over the Alps this is likely to bring significant snowfalls to the alps. If it peaks over the Tasman then it will bring cold weather with some snow, but not massive amounts.

    Another quirk of Jet streams is that if you look at a chart which shows where the are you will see that they slow down and speed up as they move around the globe. Where they slow down is where the strongest low pressure systems are likely to develop, but on the righthand side of the jet in the southern hemisphere and the left hand side in the northern hemisphere. This is often referred to the right and left jet exit respectively.


    Consequently if significant low pressure systems develop here then it is also likely that significant cold fronts will also develop and push northwards here as well.

    One last thing is that where the Subtropical and Polar jets converge is also a good place for frontal activity because of the strong thermal gradient and therefore instability in this region.


    Hope that helps.
     
    #3 Falls expat, May 9, 2006
    Last edited by a moderator: Nov 17, 2013
  4. Yardsale

    Yardsale Part of the Furniture Moderator

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    Nice reply. Now, can some one send that to the pool room for safe keeping?
     
  5. Sandy

    Sandy Dark Sith Lord of the Pool Room Moderator Ski Pass: Gold

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    Falls, a question...

    Is there any cyclic patterns with jetstreams??

    While the paramters may be very complex, they seem to be very well defined in terms of characteristics and range of location.
     
  6. Falls expat

    Falls expat One of Us

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    Here is the NoGaps T+48hrs 300hpa winds which hopefully will update each day and may help with my explanation above.

    [​IMG]

    Here is the corresponding Surface pressure and precip chart to monitor where lows develop and move.
    [​IMG]
     
    #6 Falls expat, May 10, 2006
    Last edited by a moderator: Nov 11, 2013
  7. Bugski

    Bugski A Local

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    Fantastic! Thanks Falls!
     
  8. Falls expat

    Falls expat One of Us

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    Interesting question Sandy, one which I was going to comment on soon anyway as it happens.

    Last weekend I attended the Reading University (UK) Meteorology dept 40th anniversary .

    Whilst there they had various labs showing off experiments, including my all time favourite which is the Rotating Annulus. This is doughnut shaped round tank which is filled with liquid which has near neutrally buoyant silvery particles in it. The centre of the tank (i.e. the hole of the doughnut) is refrigerated and the outer edge is heated. The whole tank is placed on a rotating table which rotates at the same rotational speed as the earth.

    The experiment is usually left overnight rotating to find some sort of equilibrium.

    The liquid in the tank represents the atmosphere of the earth. It is remarkable to see when its operating because the quasi-equilibrium achieved looks very similar to the upper flow around the southern hemisphere. By this I mean the heating and cooling within the rotating tank sets up jetstreams of moving fluid (relative to the tank) which move to and from the cold centre (equivalent to the poles) out to the warmer sides (equivalent to the tropics).

    Every time I have seen this experiment it done it has produced 4 nodes or trough/ridge pairs. However, the head of fluid and ocean dynamics at Reading Uni told me it can be 2 or 3 nodes as well, but he also said that once it gets to 4 nodes then it is only a matter of time before it becomes unstable and the nodes, troughs or waves (what ever you want to call them) break up ending in a period of chaotic seemingly random mixing of mini eddies probably equivalent to lots of cut off lows. Once this occurs it then gradually stabilises again to form more stable nodes again and the process is repeated.

    Sorry for the long winded explanation, but I though it made sense of some comments I have often heard on this forum about the number of nodes rotating around the southern hemisphere.

    It seems to me that if you have 2 or 3 nodes then the jet streams will follow fairly similar and probably more predicable paths. However, once 4 nodes become achieved then it would become less predictable.

    When you take onboard what I have said above and then throw in significant heating anomalies along the tropics, such as land masses and warmer and colder sea areas then these are likely to lead to zones of preferred troughing and ridging. This is what has been observed.

    So, as far as cycles are concerned, I think the two main features to look out for are probably the number of nodes in the circumpolar flow and how they are located regarding the semi-permanent heating anomalies over the tropics.

    Phew!! [​IMG]
     
    #8 Falls expat, May 10, 2006
    Last edited by a moderator: Nov 17, 2013
  9. Falls expat

    Falls expat One of Us

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    Here are some top view pics of the evolution of a differentially heated Annulus experiment.

    [​IMG]

    Here is a 3D model view of the same experiment [​IMG]

    From Here For those who enjoy reading further.


    Oh and this is what the real thing looks like. View looking down at the south pole with 1000-500mb thickness contours and sea surface pressure
    [​IMG]

    And 500mb height contours in deca-metres.
    [​IMG]
     
    #9 Falls expat, May 10, 2006
    Last edited by a moderator: Nov 14, 2013
  10. BrentC

    BrentC Hard Yards

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    Thanks for that Falls! From your picture, I didn't realise that the Jetstream isn't actualy a continued band that circumnavigates the atmosphere, but rather starts and stops at intervals. Cool.
     
  11. Sandy

    Sandy Dark Sith Lord of the Pool Room Moderator Ski Pass: Gold

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    Whoaaaaaa [​IMG]

    That's incredibly interesting!!!! [​IMG]

    Might be worth more of a look...
     
    #11 Sandy, May 10, 2006
    Last edited by a moderator: Nov 11, 2013
  12. Oyster

    Oyster First Runs

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    Great job Falls! alot of :nerd: weather stuff usually goes straight over my head, but you made it very clear to me. :cheers:
     
  13. POW_hungry

    POW_hungry Part of the Furniture Moderator Ski Pass: Gold

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    Great job Falls. Meteorology is full of endless information... I can't wait to learn more.
     
  14. Ijay

    Ijay Hard Yards Ski Pass: Silver

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    Another impressive post from Falls Ex, really very helpful.

    (all that is needed now is a post from CF and I'll be totally swamped [​IMG] )
     
    #14 Ijay, May 11, 2006
    Last edited by a moderator: Nov 11, 2013
  15. board freek

    board freek One of Us

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    good work falls i understood that very well
     
  16. BlueMountains

    BlueMountains First Runs

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    Further to Falls helpful posts, I thougth I would post the BoM's smoothed version of upper level patterns, sometimes referred to as the Long Wave Trough (or Rossby Wave) and indeed the Long Wave Ridge. I use the 5400 line to observe the troughs and ridges in the upper levels. The troughs are the loops or nodes or waves (some of their common names) where the 5400 line peaks and the ridges are when the 5400 line dips, like a ridge. So as Falls suggests, look for the Long Wave Trough in the link below as it peaks over the south east of Oz and cold fronts can form to the right of them at the surface. I like to see the nodes or troughs being quite well defined and not flat as they move towards Oz, as this suggests sharper definition of cold air intrusion and possibly stronger fronts. And yes, from what I know when there are fournodes or more its only a matter of time before chaos sets in and hopefully produces something good! I also like the 5400 line from the smoothed drawing below to be near 40 degrees south otherwise the jetstream doesn't really strengthen over Australia but that is merely my interpretation and others may add more.


    http://www.bom.gov.au/cgi-bin/nmoc/latest_D.pl?IDCODE=IDX0517
     
    #16 BlueMountains, Jul 21, 2006
    Last edited by a moderator: Nov 14, 2013
  17. snwbrdr

    snwbrdr First Runs

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    How do I submit a few Pics of a jet stream that came over the Range to Maffra recently, it was huge. [​IMG]
     
    #17 snwbrdr, Aug 7, 2006
    Last edited by a moderator: Nov 11, 2013
  18. Falls expat

    Falls expat One of Us

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    Try uploading them on Darb.net

    Go to Album actions on top right and select add photos.

    Once you upload the photos:

    Left click on the added photo to open them up on Darb.net

    Then right mouse click on the open photo and select properties from the drop down box.

    Copy the web (URL) address of the photo.

    Go to a full reply form on the Ski.com.au forums and click on image and then paste the photo address into the space provided.

    When you submit your reply the photo will become viewable to forum members.
     
  19. snwbrdr

    snwbrdr First Runs

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    Cool, thank you for that, they shall be on their way.....
     
  20. snwbrdr

    snwbrdr First Runs

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    [​IMG]

    [​IMG]

    Thank you, here they are.
     
  21. snwbrdr

    snwbrdr First Runs

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    That didn't seem to work on my side of the equation.... Ok there in Darb net anonymous area..
     
  22. TropicalBoy

    TropicalBoy Hard Yards

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  23. TropicalBoy

    TropicalBoy Hard Yards

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    Might as well put the pics up for you

    [​IMG]

    [​IMG]


    for future reference click on the UBB Codeâ„¢ is enabled. link to the left of the rely box, all info is there.
     
    #23 TropicalBoy, Aug 8, 2006
    Last edited by a moderator: Nov 11, 2013
  24. snwbrdr

    snwbrdr First Runs

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    Thanks mate, :thumbs: I am good with graphics, illustrator, photoshop etc.. but don't take to read the small print, but willing to learn from example. The stream on the left was double the width of the right one, and they were the only clouds in the sky that was visual.
     
  25. TropicalBoy

    TropicalBoy Hard Yards

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    I noticed a similar type of cloud setup the last time i flew up to Darwin from Melbourne. I would say it was about over Alice Springs out the west side of the plane, Iw as surprised with how thin the cloud seemed to be. Altought it was a fair way off in the distance as the seemed to be trying to keep away from it as much as possible. Didn't get any pics as the camera was in the luggage hold, was kicking myself to.
     
  26. M-HD

    M-HD First Runs

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    Nice stuff!!

    I've just started some further study of this stuff (among other things)...

    The interesting thing for me is the similarity with our own Zonal flows (Jets, trades etc) and a zonal flow set up on other planets and for that matter in things like terestrial plasmas and oceans....

    AFAIK Jets are a seasonal certanty (for now..) you look at the ncar seasonal average winds at 250mb you see that year to year we get the strong jets due to the gradient (change) in heating... while the sun is directly over head (summer) heating is not a strong function of lattitude, but while it is in the north (winter) the angle of incidence on the ground and the local re-radation and hence heating is a strong function of how far south you are and winds move to cancel out this thermal gradient....

    This is one of the reasons why avation forcasters are busier in the winter as there is much more vertical and horizontal shear resulting in clear air turbulence which needs to be forcasted...
     
  27. Ossie bloke

    Ossie bloke First Runs

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    Falls expat.

    Your explanation suffers badly. Looking at geoligical evidence. Looking at mythologic evidence, there is no way that you are correct.

    There were two giant ice sheets in the Northern hemisphere recently. Your heat exchange and gravity driven theory cannot explain this.
     
  28. Ossie bloke

    Ossie bloke First Runs

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    M-HD

    Qouting you... "local re-radation"
    Radiation cannot re-radiate.

    From this webpage;-

    http://www.ems.psu.edu/~fraser/Bad/BadGreenhouse.html

    Does the atmosphere reradiate?
    One often hears the claim that the atmosphere absorbs radiation emitted by the Earth (correct) and then reradiates it back to Earth (false). The atmosphere radiates because it has a finite temperature, not because it received radiation. When the atmosphere emits radiation, it is not the same radiation (which ceased to exist upon being absorbed) as it received. The radiation absorbed and that emitted do not even have the same spectrum and certainly are not made up of the same photons. The term reradiate is a nonsense term which should never be used to explain anything.

    Sometimes diagrams are drawn which show the radiation from the Earth's surface rising into the sky and being reflected off of the atmosphere (or clouds, or greenhouse gases). This too is nonsense. The radiation was not reflected, it was absorbed and different radiation was subsequently emitted.
     
    #28 Ossie bloke, Aug 25, 2007
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  29. shneeshwine

    shneeshwine First Runs

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    What are the temp gradiants in the experiments.Can you tell us about outer materials utilsed and protocols on stats used.
     
  30. willis

    willis First Runs

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    <div class="ubbcode-block"><div class="ubbcode-header"> PHP:</div><div class="ubbcode-pre ubbcode-body" style="height: 36px;">Question is how do jetstreams affect weather systems? </span>
    </div></div>

    Found this in a description of 11 - 13 October 2000 NZ snowstorm. Click on the link below to see the whole thing, weather maps aswell. Here is an example of how they can have an effect

    Any knowledge on that?

    http://www.metservice.com/default/index.php?alias=2000spring2194257
     
    #30 willis, May 26, 2008
    Last edited by a moderator: Dec 26, 2013
  31. willis

    willis First Runs

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    Anybody???
     
  32. Shin setsu

    Shin setsu First Runs

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    Sick low..... were is that when we need it....
     
  33. M-HD

    M-HD First Runs

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    Found this in a description of 11 - 13 October 2000 NZ snowstorm. Click on the link below to see the whole thing, weather maps aswell. Here is an example of how they can have an effect

    Any knowledge on that?

    http://www.metservice.com/default/index.php?alias=2000spring2194257 </div></div>

    Yes.. plenty of knowledge on that..

    A Jetstream is a area of local maxima in winds above ~500hPa (although you do get jets below that, for example nocturnal jets just above the surface etc..)

    This is in general caused by strong temperature gradients and two classical climatological examples exist: The subtropical jet just below the string of high pressure systems and the polar front jets above the low pressure systems.

    Now there are three things required to produce snowfalls: Cold (enough) temperatures, instability, and moisture.

    In the southern hemisphere the left entrance and right exit of a jet streak will enhance upward flow and instability and hence possible precipitation.

    This can be explained through a variety of meteorological phenomena (confluence/diffulence, conservation of potentiality vorticity)

    So, if I were to engineer a nice snowfall situation I would have nice cold air and strong thermal gradient generating a mid tropospheric polar front jet with the left entrance over the alps. Then turn that into a cut off system and a east coast flow of moist air and you have a dump...

    (disclaimer: I may have got my left entrance etc... the wrong way around... all my reference material is at work...)
     
    #33 M-HD, Jun 15, 2008
    Last edited by a moderator: Dec 26, 2013
  34. willis

    willis First Runs

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    Didn't understand much of that but thanks for responding. I'll have to suss it out myself I think
     
  35. SnowAndrew

    SnowAndrew One of Us

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    Is there a reason this topic is sticky and comes up at the top all the time?
     
  36. cold wombat

    cold wombat Twitter Contributer Moderator Ski Pass: Gold

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    So that the contained wisdom is not lost when weather clueless peeps like me come along and learn lots from it.
     
    #36 cold wombat, Feb 29, 2012
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