Back to the trails. Why are the trails sometimes gone after a short time, or nearly not visible and on other days they stay a long time in the sky? I guess, we notice them more often, when they are longer visible. It has nothing to do with the substance in it, it is caused by the special waether conditions.

Thanks for the hint. I have to dive into that topic. On the other hand, there is so much to study. This morning I saw some disturbing stuff about G5 towers which cause birds falling out of the sky...