Vapour Trails
I have a question about vapour trails/contrails.
Having spent some time in Europe, I have noticed that there are almost always aircraft making vapour trails - these are more pronounced in winter, in my experience. However, in Southern Africa, one hardly ever sees vapour trails. I know that this is most likely due to the fact that we have relatively little high altitude jet traffic, but am still interested.
I wonder if anyone could explain the vapour trail phenomenon - why do they form, in which conditions are they seen, and whether altitude has any effect on them at all - i.e. is there an altitude below which they never form?
Thanks in advance for the help - sorry if this has been asked before.
Tx
Mike