View Full Version : Practical Meteorology question....
757jetjockey
11th Jan 2006, 19:00
Just a quick question guys which has been bugging me and severla colleagues for some time now. On the UK Sig Wx charts where a jet stream is present with an area of CAT, just below the indicated height of the Jet, eg FL370 there is some text below for example (-70/+130). Just want clarification on what this means, as so far have had about ten different explanations..
Rgds
JetJockey :ok:
-IBLB-
11th Jan 2006, 19:50
I believe that the altitude given at the chart is the core of the jet, the +xxx/-xxx is the altitude in hundreds of feet up and down from the core altitude that the jetstream is still present. Doublecheck for sure though...
High Wing Drifter
11th Jan 2006, 19:55
Good question and will my extra strength Google goggles I found this:
http://www.metoffice.com/aviation/services/WAFC_update_brochure.pdf (page 4)
It refers to the height in hundreds of feet above and below an 80kt isotach. I don't recall a mention of 80kts isotachs in ground school :confused:
-IBLB-
11th Jan 2006, 20:00
Good question and will my extra strength Google goggles I found this:
http://www.metoffice.com/aviation/services/WAFC_update_brochure.pdf (page 4)
It refers to the height in hundreds of feet above and below an 80kt isotach. I don't recall isotach in ground school :confused:
isotach = line of equal windspeed
so the numbers given are the relative altitudes in 100s of feet in relation to the core, where the wind is still 80 knots or greater. (the core is in between two 80 knots isotachs)
High Wing Drifter
12th Jan 2006, 10:15
I meant to say that I hadn't come acorss 80kt isotachs in Ground School.
I wasn't sure why the thickness of the jetstream is bounded by a min wind speed of 80kts when the defintion of a jetstream includes a minimum speed of 60kts. So I found this document (http://www.wmo.ch/web/aom/amprog/Documents/PROMET-Geneva-2001/Doc-3-1(4).doc)
Feedback from IATA has led to a recommendation for the addition of information about the vertical extent of the 80-knot wind envelope displayed.
Funny, but I handn't registered that these people exist: http://www.iata.org/index.htm
pugzi
12th Jan 2006, 19:19
well bowl me over, there is something that even I didn't know. The old saying rings true, you learn something new every day.
I need to sit down, I'm shocked. I feel a newbie.
Steve