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  • Q1985 Help!

    Can someone please help me understand why the answer to this question is "with a warm front"? I have drawn a total blank here!

    Q is as follows:
    A wind sounding in the region of a polar front jet stream gives the following wind profile (Northern hemisphere): 900hPa 220/20kt; 800hPa 220/25kt; 700hPa 230/35kt; 500hPa 260/60kt; 400hPa 280/85kt; 300hPa 300/100kt; 250hPa 310/120kt; 200 hPa 310/80kt. Which system is the jet stream associated with?

    A) With an easterly wave
    B) With a ITCZ
    C) With a warm front
    D) With a cold front

    Any help would be gratefully received!


  • #2

    I'm not a "metman" but maybe this explanation will help - subject, of course, to confirmation from Ken.

    Answer (a): the quoted winds are, more or less, westerly and they increase steadily with altitude. There would therefore appear to be no easterly thermal component.

    Answer (b): we are talking about the polar front, so the ITCZ is irrelevant.

    Answers (c) and (d): polar front jets flow parallel to the frontal surfaces of a polar front depression. Now, imagine the 'traditional' picture of such a depression - the fronts form an inverted 'V' with the cold front running SW to NE to the centre of the depression and the warm front running NW to SE from the centre. So, the jet flows from the SW along the cold front and from the NW along the warm front. The jet winds in the question (eg 250 hPa) are NW'ly, so it must be a warm front.

    Last edited by BobC; 21-05-2005, 16:59.


    • #3
      Many thanks for that Bob, it makes sense now!



      • #4
        Hi Sue

        Thanks BobC, you are spot on.

        It specifies in the northern hemisphere, and the polar front jet stream, and we know the jets blow from the warm air (high pressure aloft) to the cold air (low pressure aloft) deflected to the right by Coriolis.

        In our vicinity the polar front is more or less west to east with a bit of deflection because of the warm Gulf stream in the Atlantic. The warm air is to the south and the cold air is to the north, so the jet stream blows from west to east, about 270 degrees. This is if there is no depression causing polar front activity.

        If there are warm and cold fronts the normal arrangement is to have the warm sector in the center sector (south) of the depression, so the warm front will be to the east of the cold front.

        Now if we look at the flow from warm to cold deflected to the right, the jet stream in the vicinity of the warm front will be anything from about 270 degrees to about 360 degrees. In the vicinity of the cold front the jet stream will be anything from about 270 degrees to about 180 degrees. In this one the core is 310 degrees, so it must be in the vicinity of the warm front.

        Hope that helps you.



        • #5
          Hi Ken, i am sorry can you please explain this again in a simpler format.

          Thank you