 Follow us on Twitter
20592 Members
35 Forums
32872 Topics
953546 Posts
Max Online: 404 @ 14/07/10 05:00 pm
|
|
|
Jetstream Question
#91999 - 06/05/06 06:22 pm
Jetstream Question
|
BrentC
Been Here a While
|
Offline
|
|
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!
|
|
Top
|
|
|
|
|
#92000 - 09/05/06 05:34 pm
Re: Jetstream Question
|
BrentC
Been Here a While
|
|
Offline
|
|
Bump Bumpety :woohoo:
|
|
Top
|
|
|
|
|
#92001 - 09/05/06 06:54 pm
Re: Jetstream Question
|
Falls expat
Dedicated
|
|
Offline
|
|
Originally posted by BrentC:
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!
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.
_________________________
Civilization had too many rules for me, so I did my best to rewrite them!
|
|
Top
|
|
|
|
|
#92002 - 09/05/06 09:04 pm
Re: Jetstream Question
|
Yardsale
mastering the art of stacking since '93
Part of the Furniture
|
|
Offline
|
|
Nice reply. Now, can some one send that to the pool room for safe keeping?
|
|
Top
|
|
|
|
|
#92003 - 10/05/06 10:28 am
Re: Jetstream Question
|
Sandy
Dark Sith Lord & Gold Skigie 2006
Old and Crusty ;)
|
Online
|
|
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.
|
|
Top
|
|
|
|
|
#92005 - 10/05/06 06:37 pm
Re: Jetstream Question
|
Bugski
Part of the Furniture
|
|
Offline
|
|
Fantastic! Thanks Falls!
|
|
Top
|
|
|
|
|
#92006 - 10/05/06 06:39 pm
Re: Jetstream Question
|
Falls expat
Dedicated
|
|
Offline
|
|
Originally posted by Sandy:
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.
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!! 
_________________________
Civilization had too many rules for me, so I did my best to rewrite them!
|
|
Top
|
|
|
|
|
#92008 - 10/05/06 07:07 pm
Re: Jetstream Question
|
BrentC
Been Here a While
|
|
Offline
|
|
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.
|
|
Top
|
|
|
|
|
#92009 - 10/05/06 07:12 pm
Re: Jetstream Question
|
Sandy
Dark Sith Lord & Gold Skigie 2006
Old and Crusty ;)
|
|
Online
|
|
Whoaaaaaa
That's incredibly interesting!!!! 
Might be worth more of a look...
|
|
Top
|
|
|
|
|
#92010 - 10/05/06 09:11 pm
Re: Jetstream Question
|
Oyster
Dedicated
|
|
Offline
|
|
Great job Falls! alot of :nerd: weather stuff usually goes straight over my head, but you made it very clear to me. :cheers:
|
|
Top
|
|
|
|
|
#92011 - 11/05/06 07:27 pm
Re: Jetstream Question
|
POW_hungry
Addicted
|
|
Offline
|
|
Great job Falls. Meteorology is full of endless information... I can't wait to learn more.
|
|
Top
|
|
|
|
|
#92012 - 11/05/06 09:34 pm
Re: Jetstream Question
|
Ijay
Been Here a While
|
|
Offline
|
|
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  )
|
|
Top
|
|
|
|
|
#92013 - 26/05/06 08:21 pm
Re: Jetstream Question
|
board freek
Dedicated
|
|
Offline
|
|
good work falls i understood that very well
|
|
Top
|
|
|
|
|
#92014 - 21/07/06 09:42 am
Re: Jetstream Question
|
Blackheath
Been Here a While
|
|
Offline
|
|
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
|
|
Top
|
|
|
|
|
#92015 - 07/08/06 11:29 pm
Re: Jetstream Question
|
snwbrdr
Been Here a While
|
|
Offline
|
|
How do I submit a few Pics of a jet stream that came over the Range to Maffra recently, it was huge. 
|
|
Top
|
|
|
|
|
#92016 - 08/08/06 12:27 am
Re: Jetstream Question
|
Falls expat
Dedicated
|
|
Offline
|
|
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.
_________________________
Civilization had too many rules for me, so I did my best to rewrite them!
|
|
Top
|
|
|
|
|
#92017 - 08/08/06 09:42 am
Re: Jetstream Question
|
snwbrdr
Been Here a While
|
|
Offline
|
|
Cool, thank you for that, they shall be on their way.....
|
|
Top
|
|
|
|
|
#92018 - 08/08/06 10:11 am
Re: Jetstream Question
|
snwbrdr
Been Here a While
|
|
Offline
|
|
[img]http://darb.net/anonymous/Jet_stream[/img]
[img]http://darb.net/anonymous/Jet_stream_1[/img]
Thank you, here they are.
|
|
Top
|
|
|
|
|
#92019 - 08/08/06 10:16 am
Re: Jetstream Question
|
snwbrdr
Been Here a While
|
|
Offline
|
|
That didn't seem to work on my side of the equation.... Ok there in Darb net anonymous area..
|
|
Top
|
|
|
|
|
#92021 - 08/08/06 01:25 pm
Re: Jetstream Question
|
TropicalBoy
Emerging
|
|
Offline
|
|
Might as well put the pics up for you
for future reference click on the UBB Code™ is enabled. link to the left of the rely box, all info is there.
|
|
Top
|
|
|
|
|
#92022 - 08/08/06 11:17 pm
Re: Jetstream Question
|
snwbrdr
Been Here a While
|
|
Offline
|
|
Thanks mate, :thumbsup: 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.
|
|
Top
|
|
|
|
|
#92023 - 10/08/06 08:07 am
Re: Jetstream Question
|
TropicalBoy
Emerging
|
|
Offline
|
|
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.
|
|
Top
|
|
|
|
Moderator: Sandy, Claude Cat
|
