Having got my head round the idea that the planes over us are into the stratosphere and that this is because there is a lack of turbulence in the lower stratosphere, it then occurred to me that I had noticed vapour trails being dispersed by the wind. I noticed two trails at 90 degrees to each other like the Scottish saltire legend. They both spread laterally which suggests that the lateral spreading is not due to wind or that the winds are at 90 degrees to each other in two close high layers of air. A little research: I had heard the phrase contrail before and now understand that it is "condensation trail" from the water vapour produced by combustion of the fuel. Research suggest that these trails can become cirrostratus cloud but this doesn't exist in the stratosphere. Hence I conclude that these planes may well not quite have been into the stratosphere.
