Looking out of my window around sunset this evening I noticed a succession of planes lining up from the west, all with short contrails except one which was leaving a lengthy persistent trail. I thought it would make quite a good illustration of how "adjacent" flights can be at very different altitudes, so I looked up the flights on FR24 and annotated the photo here:
The only persistent trail is from the very high altitude private Gulfstream. The trails at 39,000ft and 41,000ft are slightly longer than the ones at 37,000ft, once you take into account the fact that they are much more distant.
That's not to say that higher flights will always have more persistent trails, of course. It depends on the atmospheric profile at the time,. Sometimes I've seen planes at 29,000 feet leaving persistent trails while those at 34,000 feet were hardly leaving any.
The only persistent trail is from the very high altitude private Gulfstream. The trails at 39,000ft and 41,000ft are slightly longer than the ones at 37,000ft, once you take into account the fact that they are much more distant.
That's not to say that higher flights will always have more persistent trails, of course. It depends on the atmospheric profile at the time,. Sometimes I've seen planes at 29,000 feet leaving persistent trails while those at 34,000 feet were hardly leaving any.
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