1. Ross Marsden

    Ross Marsden Senior Member

    Does anyone know what altitude Ethiopian 501 was at over Halifax?
    The UTC time was 0434 UTC 23 Jul 2017.
  2. Mick West

    Mick West Administrator Staff Member

    31,000 feet, like I said. :) Level flight.


    A quite plausible altitude for aerodynamic contrails.
  3. Ross Marsden

    Ross Marsden Senior Member

    For what they are worth, here are the temperature and humidity soundings around that time (1630 UTC) in the vicinity of Halifax on 23 July 2017.

    31000 feet is at 287.4 hPa.

    Sable Island is off shore to the southeast of Halifax, and Yarmouth is at the west end of the peninsula.

    The temperature is too warm for exhaust contrails by over 10 degrees.

    For reference, here is a table of the Critical Contrail Temperature for high bypass engines from Schrader's letter.


    The RH, while known to be in error and too low, seems low for aerodynamic contrails as well.

    Nevertheless, aerodynamic contrails seem to me the most plausible explanation.
  4. Mick West

    Mick West Administrator Staff Member

    Probably not a lot unfortunately. As discussed several times previously the raw spot readings are too low resolution to be useful - although they do give an interesting vertical picture of how layered the atmosphere is. We need to look at maps generated from a full atmospheric model. This is an hour early and 250mb is a bit too high, however it shows the regions of the atmosphere much better than the spot soundings.
    The small red circle is the Halifax. Arrows indicate the wind direction. The contrail seems to have formed approximately at the boundary between regions of high and low humidity.
    Last edited: Aug 9, 2017
  5. Ross Marsden

    Ross Marsden Senior Member

    The main point of posting that data was to rule exhaust contrails in or out on the basis of the ambient temperature.
    Far too warm, so, Out.
  6. Mick West

    Mick West Administrator Staff Member

    Aha, yes sorry, the temperature readings are both more accurate and with a lot less variation.

    That 1500Z -43.8°C from earth.nullschool.net matches the 12Z WSA Sable Island 250hPa temperature. 250 hPa is about 35,500 ft, so yes, I'd agree that it was too warm for exhaust contrails at 31,000 feet. Aerodynamic it is! (probably)
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  7. TEEJ

    TEEJ Senior Member

    Here is another one that you guys might like to identify!

  8. Mick West

    Mick West Administrator Staff Member

    Something similar, from "Spacious Skies", 1989. Photo from 1987
    12.5 Contrail in Rippled Sky 1987.

    This is not exactly the same though. The contrail is continuous, and is being distorted, with some gaps possibly forming.
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