Expert: Marc Ebelini - 4/22/2009

Question
Hello and good day, after watching airplanes in flight at different altitudes I am wondering why the contrails are so much different even when planes are at the same altitude,  some differences noted are contrails which are small and disperse with  in a few minuets, however some of these are seen stretching the sky as far as my eye can see when viewed in my 50x80 binoculars the contrails which stay around for a while look different when emitted from the back of the planes, they are very polluting looking upto 5 trails seen coming off the planes. Why is this is this is it something to do with the fuel? I eliminated the weather as cause for these differences, as they are seen in what ever weather, I am confused, I have heard of a thing called chemtrails are these the cause and if so what are they?
Kind regards

Answer
While this question may be a little out of my ares of expertise. As a pilot. I've known the the cause to be associated with the weather. Not necessarily the weather on the ground but up at their altitude. The condition is generally caused by the crystallization of the moisture emitted by the engines. Can tell from personal experience that the temperature and humidity varies at the different altitudes. There is the dry adiabatic lapse rate and the moist rate so one cannot accurately predict the temperature or moisture accurately any given altitude. Therefore what you assume is the same altitude may not be so in actuality. Air currents do not travel precisely horizontally. An airplane flying over a different area may encounter different conditions at the same altitude. To illustrate from one of my experiences. I was piloting one aircraft that was leaving at the same time as another. We both were headed to the same destanation. The winds aloft were not favorable. I was told that the winds was less severe two thousand feet higher (altitudes are designated by direction of travel) So I selected the fight plan at that altitude only to look down at the slower aircraft over take me and was making better time.
That is the nature of weather predictions. The same applies to moisture and temperature. A metrologist can probably explain it better. But I hope this helps somewhat.