1. Spectrar Ghost

    Spectrar Ghost Senior Member

    Based on context I'd presume it's a reduction in surface temperature of 0.159C.
     
    • Agree Agree x 2
  2. Graham2001

    Graham2001 Active Member

    A 1905 book on clouds has been uploaded to Project Gutenberg, the scans of the illustrations are not perfect, but the show quite clearly that clouds back then look like clouds now.

    Cloud Studies by Arthur W. Clayden (1905)

    http://www.gutenberg.org/ebooks/55126

    The authors introduction recommends the book to meteorologists, artists and anyone who is interested in the sky.
     
    • Like Like x 1
    • Informative Informative x 1
  3. SR1419

    SR1419 Senior Member

    • Like Like x 2
  4. mikret

    mikret New Member


    can persist for hours - --
    I'm not sure that a few hours, but I'm sure that I watched 30-40 minutes ..
    everything depends on the weather and the airplane.
     
  5. Mick West

    Mick West Administrator Staff Member

    To see them persist for hours you usually have to look at satellite image, as the wind has generally carried them out of view after a couple of hours. They also spread out, and it's hard to distinguish them from other clouds.

    I think more commonly people see contrail cover that last hours, and don't realize it's from different contrails. Like:

    Source: https://www.youtube.com/watch?v=kQekGClN5GE
     
    • Like Like x 2
    • Agree Agree x 2
  6. L. Baker

    L. Baker New Member

    There are many things to consider when talking about contrail formation. Just off the top of my head, and not in any particular order:

    1. Atmospheric profile (temperature, humidity, and pressure with respect to height.)
    2. Partial vapour pressure with respect to ice.
    3. Partial vapour pressure with respect to water.
    4. Condensation (or sublimation) nuclei.
    5. Cosmic radiation levels.
    6. Fuel and exhaust gas composition.
    7. Aircraft velocity.
    8. Aircraft elevation.
    9. Aircraft type
    10. Engine types and configuration.
    11. Wake turbulence.
    12. Exhaust turbulence.
    13. Exhaust velocity and volume.
    14. Atmospheric winds
    15. Season
    16. Time of day
    17. Latitude and longtitude
    16. Angle of view
    17. Sizes, shapes, and properties of constituent water droplets or ice crystals.
    18. Additional layers of clouds or contrails)
    .

    Remember that all of these things determine what a contrail will look like from the ground. You cannot start with the "look" of or shape of a contrail and make statements about what all the determining factors are. That is pure silliness and is a trap that many fall into.
     
    Last edited by a moderator: Nov 24, 2017
  7. Mick West

    Mick West Administrator Staff Member

    [​IMG]

    This has been posted before, but the version I saw before was the reprint without the last paragraph. This is the original, from:
    https://books.google.com/books?id=N...ts=bpfzssIufW&pg=RA4-PA13#v=onepage&q&f=false

    It's interesting because even back then, in the very first few times that planes had flown at that altitude, the causes of contrail cloud formation were broadly understood.
     
    • Like Like x 3
    • Useful Useful x 2
    • Informative Informative x 1
  8. SR1419

    SR1419 Senior Member

    That description has it all; persisting, spreading, gaps...even a distrail! nice find.
     
  9. Mick West

    Mick West Administrator Staff Member

    Lieutenant MacReady was quite the badass back then, there's more detailed accounts of his flights here:
    https://media.defense.gov/2011/Apr/25/2001330216/-1/-1/0/110425-D-LN615-004.pdf

    With some early chemtrailing (Actually cropdusting, also in 1921):
    Metabunk 2018-02-17 10-26-14.

    His own account of the 1921 flight (attached) is fascinating, although he does not mention the contrails — presumably not having seen them form behind him (or it might actually have been a later flight)
     

    Attached Files:

    Last edited: Feb 17, 2018
    • Like Like x 1
  10. Mick West

    Mick West Administrator Staff Member

    • Like Like x 2
  11. Graham2001

    Graham2001 Active Member

    Not a book, but a 1920 film (With modern royalty free music.) about clouds by the US Department of Agriculture, again it shows that clouds back then are no different from clouds now.

     
    • Like Like x 1