Iridescent Aircraft Trail
The vivid colours were visible until the contrail itself began to weaken as the plane reached a less humid air mass. The sequence of images [below] shows how the trail changed and developed gaps as the humidity decreased. Very soon after the last pic the contrail formation stopped and the plane flew without a trail.
You can also see some faint shadow cast by the plane across the humid air.
Back home I checked flightradar24.com for the details of the plane. It was a Boeing 747 cargo plane of Singapore Airlines flying east from Dallas and Brussels at 10,058m [33,000ft] high and 883 km/h [550mph]."
|Aircraft contrails have two sources. The major one is water droplets condensed from water vapour generated in the engines. Combustion of aviation fuel gives water vapour, carbon dioxide and traces of NOx and soot. Opaque engine trails are prominent in Monika’s images. The second generator is water vapour already in the air condensed to droplets by airflow over the fuselage and wings. Air passing over the top of wings or convex fuselage sections travels faster, expands and cools. Sometimes, if the air is sufficiently humid, water vapour then condenses out into a fine droplet mist. These airflow droplets appear to be the source of the iridescence in Monika’s trail.