View Full Version : Jet stream
21st Apr 2012, 07:26
one is never bored due to being puzzled by how much one does not know :(. Looks like everyone except me knows about jet stream that makes long distance flight duration longer or shorter depending on which way is headwinds. So I educated myself with the help of the most comprehensive educational resource (W of course) and read through this The Jetstream - What It Is and How It Affects Our Weather - Netweather.tv (http://www.netweather.tv/index.cgi?action=jetstream-tutorial;sess=) and maybe someones with experience would care to explain if the jet stream is predictable enough to know before you take off, or will one know when up there?
21st Apr 2012, 07:41
It is reported and forecast like any other weather phenomenon, including likely areas of turbulence, and the likely intensity of the turbulence so you can adjust planned flight levels, and therefore, planned fuel loads prior to departure. The forecast is usually pretty good.
Routes are often changed to take advantage of a good tail wind, or to avoid a severe headwind, even on shorter routes nowadays. Fuel efficiency is king given the current fuel prices!
I am not sure if there is a free website that will allow you to see the relevant charts with the jetstream marked up, but I am sure that someone can point you in the right direction.
21st Apr 2012, 07:51
probes - Yes, Jet Streams are predictable and are shown on the weather charts that pilots collect at briefing, they are usually shown as a thick black line with an arrow head and the flight level(s) and speeds that it can be expected at.
In the airline world, long before the pilot sees the chart, the briefing officers will have fed the flight plan into the computer, which has also been fed all the met. information, and the flight plan produced will pick a route that either maximizes the tail wind component or minimizes the head wind component, subject to any rules governing the airways and any overfly restrictions published by the various nations.
Problems can and do arise when the head wind component is a lot stronger than forecast, personal experience is a JS of 220kts over the North Pacific that was forecast at 170kts, we had to stop off in Osaka for fuel when on our way from San Francisco to Hong Kong.
Not at home at the moment so can't reproduce a chart for you showing the JS and where you can expect to find it. Plenty of expertise here on PPRuNe so hopefully they will be along shortly!
The North Atlantic tracks vary from day to day according to the position of the Jet......and get devised and promulgated by ATC.
This can have a profound effect on the pattern of domestic airspace traffic here in the UK......we often talk of a "northabout" day for example when everyone and his dog wants to head North over the UK to start their North Atlantic crossing up near Stornoway or somewhere similar, a few days later, and aircraft will be going out through Lands End or thereabouts
21st Apr 2012, 08:13
Here you go Probes.
Jetstream Forecast - Jetstream Map Updated Four Times Daily - Netweather.tv (http://www.netweather.tv/index.cgi?action=jetstream;sess=)
21st Apr 2012, 08:57
Has nobody figured out a way of charging the Airlines for using of this Jet Stream?,hmmm could be money in this Draper,
21st Apr 2012, 09:02
Slightly off topic, Probes, but jetstreams are sometimes, but not always, accompanied by an area of severe clear air turbulence (CAT) on either side (think of the jetstream as the motorway, and the areas of CAT as the hard shoulders.) Once you are in the jetstream, the CAT is not a problem, and you are either zooming along happily anticipating a cold beer an hour earlier than usual, or else crawling across the chart, wondering if you're ever going to get there (see parabellum's post above).
21st Apr 2012, 09:38
Plenty of expertise here on PPRuNe...
that's another thing that's the source of constant awe.
So, even the regular flights are different depending on what's going on 'up there'?
And, as you know now I'm dumb anyway, I could as well confess I used to think planes fly mainly because they've got wings... :\ and never thought about the pilots' and ATCs' component in the lot.
21st Apr 2012, 10:19
Here's another source for jetstream forecasts amongst other things from the major different computer weather models.
weather model gfs europe jet stream/height 300 hpa 6 gmt + 192 wind weatheronline (http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=euro&MODELL=gfs&MODELLTYP=1&BASE=-&VAR=jet3&HH=252&ARCHIV=0&ZOOM=0&PERIOD=&WMO)=
North Atlantic Westbound tracks for today. The yellow line is the jetstream whch flows from West to East, and is a headwind for anyone heading West.
21st Apr 2012, 10:41
The funny little arrows point into wind and the markings are a chevron for every 50 kts, a large tick for 10 kts and half a tick for 5 kts. The speed of the jet over Newfoundland is 150kts. South of Ireland, it's 85kts.
The jet is a strange beast with the strongest winds being found in the polar night jet i.e. the months when the pole is in permanent darkness. I think I was told that 300kts is not unknown and the jet can be sometimes found at extreme altitudes at around the 50mb level. 300mb (30,000 feet or so) is more common.
Riding The Jetstream by John Christopher is an excellent book describing balloonists attempts to use the jetstream to fly as far as possible culminating in Bertrand Piccard and Brian Jones (great bloke) making it all the way round the world in Breitling Orbiter III. A quick trip to the south american river website is well worth the money.
21st Apr 2012, 10:51
I believe the Jetstream was discovered by the Japanese,they employed it to float those paper balloon bombs over to the USA.
21st Apr 2012, 11:03
Handy charts here for UK diy forecasting, at the rh side of this page:
CRWS Jet Stream Forecast Map Menu (http://squall.sfsu.edu/crws/jetstream_fcsts.html)
300 mb corresponds to around 30,000 feet
polar Jetstream south of the uk - cold
Jet north of the uk - mild
Jet over the uk - windy
Roughly speaking the surface stuff, eg Atlantic depressions are usually dragged along under the jet. that's why we've had a mostly mild winter, the polar jet has been to the north of the UK allowing SW'lies to dominate.
If you look at the current jet stream analysis (Saturday afternoon) together with this satellite animation, you'll see a strong airstream south of Ireland sweeping into France directly below the jetstream:
Weather Europe, Satellite Weather Europe, Weather Forecast, Rainfall, Clouds, Sun in Europe - Source: SAT24.com (http://www.sat24.com/)
21st Apr 2012, 11:09
Their paper balloon bombs certainly were helped by the jetstream although I doubt the Japs knew anything about it. The B-29 pilots reported being helped or hindered by strong winds at altitude although they too didn't really understand what was happening. I recall a post war Avro Lancastrian on a westbound flight over the Andes descending through cloud at the appointed time only to find that they had yet to cross the mountains due to flying into a headwind jetstream. They probably didn't have more than a second to realise they were heading into cumulo-granite.
21st Apr 2012, 11:36
Probes. Getting a flight in the air is a bit like a Formula 1 team effort. There are lots of people in lots of disciplines who bring bits of information together with the pilots making the final decisions, and the final execution of the flight. Unlike F1 who do it every other weekend airlines do it many times every day.
It is not unusual for a flight to be about to close the doors prior to departure to be given a change of route by the flight operations or flight planning department at the airline HQ because of a late change of conditions along the route. Reasons can be things like: thunderstorms causing a lot of small diversions (a bit like negotiating potholes in an otherwise straight road); an airport closure causing diversions, thereby taking up controller capacity and airspace; a change in forecast weather conditions a bit like parabellum described. At that point the crew have to make a decision about whether they have sufficient fuel for the new flight plan, or if they need to uplift a bit more. A high speed jet stream headwind may not warrant rerouting, but may be better overcome by changing flight level, usually to a lower level, but a lower level means a higher fuel burn. If the aeroplane is at or near it's maximum take off weight, or maximum performance for the departure airport then something else might have to give, ie unload some luggage, or recalculate performance or departure technique. In almost all instances something can be done quite, but one has to be aware of the options that one has, and to think fairly quickly through which one will be most appropriate.
TD et al
The japanese certainly noticed the jet stream as early as the 1920s, but their meteorological science was pretty much ignored by everyone else.....a German probably coined the term in 1939 or thereabouts, but here in the West a certain gent called Wiley Post first made use of the phenomenon between the wars.
21st Apr 2012, 12:38
Wiley Post (http://en.wikipedia.org/wiki/Wiley_Post)
21st Apr 2012, 12:39
To some extent, one can actually SEE the Jet Stream acting locally, as viewed from the ground. The Jet typically runs much higher than most clouds that are visible due to holding a lot of water vapour condensation, but the presence of high-velocity winds "herds" these lower level clouds and entire weather systems in long-reaching streams and curves that the eye can discern. View from above is much more informative than below, of course, which is one great benefit of those orbiting thingies we have now. Using those an armchair Jet-spotter can probably approximate a fair percentage of the forecast patterns that the Meteo folks turn out from more rigorous analysis.
One can imagine that Japanese fishermen, watching systems of clouds moving east across the Pacific and perhaps following while sailing under long-duration Jet Stream patterns could infer the potential speeds and stretch of distances that balloons might follow.
Some fair number of the things reached US coasts, IIRC.
21st Apr 2012, 14:07
Thank you! :D
21st Apr 2012, 16:12
Once done a TPE - LAX in the 74' with 220 knots right up our
clacker - and not much CAT either. The TAT barely moved the
whole trip. With 730 knots average GS we were really bloody
21st Apr 2012, 16:36
Click on the link below, when you get there select your region and click then double click to come off it.etc., etc., enjoy. (quite current too) courtesy of NOAA
AWC - High Level SIGWX Charts (http://www.aviationweather.gov/products/swh/)
BAMRA wake up
21st Apr 2012, 20:19
Jetstream related aviation pages:
21st Apr 2012, 23:08
I've mentioned this elsewhere, but it bears repeating just as an example of what the jet stream can do.
I had a spectacular ride in a BA 747 back in the late 1980's Boston - Heathrow (It was an early model and not RR engined )
The aircraft arrived late - over an hour after supposed departure time - from Philadelphia just ahead of a massive snow storm which was unseasonally early.
We boarded then sat on the tarmac for two hours as the aircraft was deiced, the runway ploughed and the aircraft started
The wind was so strong and blowing directly into the back of the engines that three compressor trucks in series couldn't boot the engines - it had to be piggybacked off a neighbouring PAN-AM 747
We eventually got off over three hours late, the pilot got into the jet stream and gave us a rollercoaster ride virtually all the way. We arrived more or less on time, picking up all the lost time. I seem to remember mention of a 300mph jet stream. After we landed the pilot announced that we had just accomplished the "second fastest subsonic crossing of the Atlantic".
The ride was bumpy as hell, the takeoff in the snowstorm bloody scary, not helped by a 20-strong bunch of Muslim matrons dressed in head-to-toe hijab all launching into an earnest mass wailing and praying session as we launched. If the knowledge of how bad the conditions were wasn't enough to give you the willies, they were.
I also remember the comment from the girl at the boarding gate when I asked what would happen in the flight was cancelled due to the weather. the response...."er.. with this pilot there won't be a cancellation. captain xxxxx never cancels. You will be flying whatever happens..."
22nd Apr 2012, 08:02
...."er.. with this pilot there won't be a cancellation. captain xxxxx never cancels. You will be flying whatever happens..."
not TOO bad considering he was still flying (and not dead)? :ouch: