et me explain how those contrails form. The aeroplane does notemit that water to forms the contrails, The aeroplane disturbs moisture that is already in the air causing it to condense and form the contrail. Watch on days where there is a very dry upper atmosphere, You can easily see on those dry days how short the contrail 'tails' on aeroplanes are. Hopefully that has helped you a bit?
Ah, now I see your confusion. The contrails are formed from the water produced from burning hydrocarbons in the fuel. The carbon produces CO2 and the hydrogen produces H2O. Look out the window and you will see that they form in the exhaust from the engines, not at the wing tips. Four from a four engined aircraft, two from a twin which then merge. They are not the same as the condensate produced by wing tip vortices. I take it that you have never been in trail behind a contrailing heavy. Contrail formation is an interesting topic involving partial pressures of both water and ice at the temperature and pressure at altitude. The saturation point of the different states of water are different. Look at ice formation overnight in frosty weather, water vapour sublimates directly into hoar frost (similar to contrail and ice clouds) without ever forming dew (similar to wet cloud.)
Ummm...!! - There - are - less - contrails - at - night - ... - because - there - are - less - aeroplanes - at - night.
Just try listening to any ATC frequency at 2pm and compare with 2am.
Those contrails never 'went' anywhere, they were never created!
Quite correct there are
fewer aircraft, especially shorthaul, at night and so fewer contrails. However contrails do form at night and do disperse with or without daylight. When they disperse they do increase the proportion of water vapour in the atmosphere.