Oct 192017

Sometime around the early 1990’s, the people who get excited about such things got excited about “donuts on a rope” contrails, which many assumed were the results of pulse detonation engines powering hypersonic Aurora spyplanes. Of course it turned out that these contrails, if you actually traced them to their sources, were being left behind perfectly normal jetliners cruising at substantially subsonic speeds. I see them, or something very much like them, on a regular basis. Anyone can who lives anywhere near the normal jetliner traffic lanes. I saw this one a few days ago:

Crappy photo taken with my cell phone, but it gets the idea across. The aircraft producing it was traveling at a normal rate of speed for a jetliner… as is always the case when I see these things.

So my question is: what *is* producing these regular puffs in the contrail? They look like they come on the rough order of magnitude of once per second.

 Posted by at 2:07 am
  • xvdougl

    I’m sure the chemtrail crowd has a plausible explanation.

    • hughie522

      I was going to say something along the lines of, “Yeah, every 5 seconds the plane dumps psychotropic drugs to control the populace.” 😛

  • Bob

    I’m wondering if it has to do with the flight control on the airplane. If the autopilot is working the control surfaces this might generate some vortices which will interact with the contrail.

  • Robbie

    I live near a regional airport, so I see contrails multiple times a day.

  • MzUnGu

    there is usually 2 swirl/vertices coming out of the wing tips from both sides, maybe when they meet downstream n interact. thus this.

  • znapel

    They appear to be called “contrail lobes”. Check this out: http://onlinelibrary.wiley.com/doi/10.1002/wea.2765/full

    This instability causes the two vortices to bend towards each other at quasi regularly spaced intervals, tens to a few hundred metres apart. Eventually, these bending vortices merge at these points, creating a series of ring vortices. Once formed, the vorticity in these rings advects the rings downward relative to the flight level (similar to smoke rings). Eventually, the descent rate slows as the rings weaken, terminating tens to a few hundred metres below the aircraft flight level. The descended cloud remains visible as the condensate is trapped within the vortical circulations.