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Pressure at a Cold Front and Inversion Layers

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  • Pressure at a Cold Front and Inversion Layers

    Good afternoon all,

    Hoping you may be able to shed some light on a couple of quick questions regarding cold fronts and the definitions of inversion layers;

    Figure 11.10 in Section 11 on Polar Front Depressions suggests that at a cold front, pressure would fall briefly before rising as it passes. I understand that as the front passes, the reduction of warm air aloft as the cold air undercuts will lead to an increase in pressure before becoming steady outside potential CU activity in the now conditionally unstable air behind it. What I don't understand is why the table suggests pressure would fall briefly as the front arrives. As I believe, an undercutting cold front will bring a slight increase in pressure due to the addition of colder more dense air underneath the warm sector air above. This picture is how I understand the front to look;

    Secondly, Q500966 concerns the effects on aircraft performance and visibility when passing through a subsidence inversion layer. The correct answer is given as "during a climb, the reduced air density above the inversion layer will cause a certain decrease in the aircraft performance (i.e. lift and thrust) and the pilot will experience a sudden improvement of visibility.". When I consider an inversion layer, I think of the following picture; In this case, surely the air density above the layer will be colder, more dense and as such performance would increase? I think my definition of layer may be confused with the layer as a whole versus the lowest level in which the inversion begins - can anyone clarify?

    Many thanks as always for your help!


  • #2
    Hi all, I've managed to answer Q1 of the above post due to the convective activity at the front quickly reducing pressure, but would still appreciate feedback on Q2 as I'm still getting some of these types of questions wrong. Any advice would be much appreciated!


    • #3
      The picture you get in the link in Binners post is good. Note that immediately above and below the top of the inversion layer, the temp is similar, and, in this case, the highest that is found throughout the climb, giving the lowest performance. For the exam, assume Inversions always give a sudden change in vis. and at least moderate turbulence and windshear. This eliminates 3 of the answers to Q 500966, which use words like gradual and slight.


      • #4
        Thanks Ben, i'll commit this to memory.