Oh and I would like to scientifically know why some contrails disburse 1-2 miles behind the planes, and not other, which last for 10 minutes and spread out, during a high pressure atmosphere with no clouds.
Finally a question that I can answer. (I am a retired airline pilot).
Jet Fuel (barely more sophisticated than Kerosene) is a hydro carbon. When a jet engine burns (oxidizes) a hydro carbon, one of the byproducts (an incidental or secondary product made in the manufacture or synthesis of something else) is water.
The jet thrust is intensely powerful so as it expels the water created in the combustion, it expands rapidly causing extremely fast cooling. That combined with the usual extreme cold at altitude (typically -60ish), creates a stream of ice crystals.
Whether that contrail 1:appears at all or 2: appears to be very short or 3: seems to last over the horizon, is strictly a function of the relative humidity of the airmass that the jet is flying through. Contrails can only occur in a relatively "wet" airmass. If the air is more normally quite dry at high altitude, the ice crystals sublimate into the atmosphere quite quickly... hence a very short trail or none at all.
You may have seen a jet ""conning" quite dramatically then suddenly stop. That's usually a sign that the jet has transitioned into a far dryer airmass... that often occurs when you are watching a jet that is still climbing.
