Weather School Musing...European Jet Stream

[simonjk]

Good morning,

Just wanted to point out how clear the jet stream is on this morning’s satellite pictures.

Have a look here
http://www.sat24.com/Region.aspx?country=eu&sat=ir&type=loop
and you can see the jet stream ‘arcing’ through the bay of Biscay and then into central Europe, before dipping southeast into Greece.

You can see how this ties up with the jet stream forecast for Europe at
http://www.weatheronline.co.uk/cgi-...-&VAR=jet3&HH=60&ARCHIV=0&ZOOM=1&PANEL=1&WMO=
Each of these charts is a forecast from the GFS model in 3-hour steps to midday Tuesday. The strong the jet stream, the redder the colour. As this feature lies atop of the country, and starts to head north it brings very strong winds. Gales will be widespread for much of this week, especially in the west.

Roughly speaking when the jet stream is to the south of the country like this the weather is usually unsettled over the UK with strong winds and heavy rain (tell us about it!). If you then click onto ‘Panel 2’ notice how the jet stream weakens over central Europe, but then reforms across Ireland and Scotland by the end of Wednesday. This highlights that the emphasis for the heavier rainfall will shift to the north and northwest of the UK from mid-week. The south then finds itself on the mild side of the jet stream and hence we are forecast to get exceptionally mild temperatures for mid-November in southern England.

Hope that is of interest,
Simon

 

[dylanwinter]

that is amazing

righto

sailing this weekend then

Dylan http://www.youtube.com/user/dylanwinter1

 

[sarabande]

Simon
a v useful post, thanks.

The relationship between the jet stream and lower level winds is intriguing. The jet presumably experiences a lot of "drag" at the interface with the lower level winds, and this presumably slows the jet and speeds up the lower winds, and transfers a lot of heat and energy between the two system.

I can understand the power sources of lower winds (surface heat/ evaporation etc, but what initiates and energises a jet stream please ?

thanks

 

[KristiferColumbus]

Simon
a v useful post, thanks.

, but what initiates and energises a jet stream please ?

thanks

I'd like to know the answer to that too.We are told that the jet stream has been responsible for our good & bad summers/one minutes it's up above the Shetlands & so was responsible for our previous two bad summers & this year it was reported earlier on that it was South of the British Isles (predictions of a heatwave/good summer),then there was doubt & so it went on.......but curiously no weather reporter that I listened to avidly through this summer gave an explanation for it's dancing around.Why not?

 

[simonjk]

Hi,

The jet stream is generated by the sharp temperature gradient created by the cold air from the Poles meeting the warm air travelling north from the Equator. The polar jet (the one that affects us) forms at the boundary of the Polar and Ferrel cells.

Now, the jet experiences other forces, and it meandres around the world, speeding up in places and slowing down in others. Therefore it isn't actually a complete band that circles the globe, it breaks in places.

It's these speeding up and slowling down regions which are vital for the development of surface pressure systems. These are areas of divergence and convergence and help in the rocess of rising and sinking air...where air rises weather forms, where it sinks, it improves.

Does that help?

Simon

 

[KristiferColumbus]

Hi,

The jet stream is generated by the sharp temperature gradient created by the cold air from the Poles meeting the warm air travelling north from the Equator. The polar jet (the one that affects us) forms at the boundary of the Polar and Ferrel cells.

Now, the jet experiences other forces, and it meandres around the world, speeding up in places and slowing down in others. Therefore it isn't actually a complete band that circles the globe, it breaks in places.

It's these speeding up and slowling down regions which are vital for the development of surface pressure systems. These are areas of divergence and convergence and help in the rocess of rising and sinking air...where air rises weather forms, where it sinks, it improves.

Does that help?

Simon

Yes it does & it is interesting thanks.So the jet streams dodging about & giving us varied summers is basicaly because of variations of temperature at the pole & the equator causing it to fluctuate if I understand it correctly but what causes these variations in temperature?
PS:I know the Earth rotates off axis but still should'nt the jet streams position be more predictable?

 

[simonjk]

Hi,

Variations in temperature at the poles and equator are caused by many factors. These are diurnal (rising and setting of the Sun), monthly (as the earth orbits the Sun), seasonal (ditto), annual, decadal etc....

At Weather School I teach 'The 6 Principles of Weather Physics' early in the morning session. One of these is that the atmosphere is a fluid trying to achieve equuilibrium. It can never do this, and some of the reasons for this are given above.

So therefore the jet stream is never constant and meandres around the globe, breaking up as it goes.

I know this is a shameless plug, but there is a video on the DVD about jet streams, you may find it useful.

Feel free to keep asking questions.

Simon

 

[KristiferColumbus]

Hi,

Variations in temperature at the poles and equator are caused by many factors. These are diurnal (rising and setting of the Sun), monthly (as the earth orbits the Sun), seasonal (ditto), annual, decadal etc....

At Weather School I teach 'The 6 Principles of Weather Physics' early in the morning session. One of these is that the atmosphere is a fluid trying to achieve equuilibrium. It can never do this, and some of the reasons for this are given above.

So therefore the jet stream is never constant and meandres around the globe, breaking up as it goes.

I know this is a shameless plug, but there is a video on the DVD about jet streams, you may find it useful.

Feel free to keep asking questions.

Simon

Thanks Simon it is very interesting.I think I have got a grip on this jet stream business now & like the ocean currents it can all be influenced by mans activity's/cutting down trees etc etc.
Global warming may be contentious but clearly we can have dramatic consequences for individual Country's climates.
I wish I had known how interesting all this is when I was at school & had gone to University
Regards KC.