"Edmund Lewis" wrote in message
ups.com

I've noticed at least 3 types of contrail from the ground. One the
"needle" you mention, another a longer, wider version of it where you
can see the division in the middle, this persists and widens for
several minutes then vanishes, and one that refuses to dissipate, just
spreads out and ends up turning into what looks like cirrostratus. I've
seen a lot of the latter type just lately- this is the type I think
might be meddling with the weather (though I shan't go into that here).

Quite common on the approach route to Manchester Airport over a region
that is noted for its dry (by UK standards) micro-climate.

The region is a 6 mile triangle of flats once marsh sea-shore surrounded
by low hills and is given to mists.

On sunny days these trails will last forever it seems.

When an aircraft passes through air that is nearly saturated the
vortices of the air it displaces must be equal to the mass of the craft.
Complex aerodynamics reduced to simple physics is that the air supports
the wings and the wings support the plane.

The pressure changes alone must be enough to cause condensation but as
with the vortices themselves the process is adiabatic or self contained.
If the weather was going to cloud over anyway then these things would
have formed anyway.

However some bean counters have suggested that the overall picture is
that aircraft take out the high and low points.

What that ammount to is that while overall temperature change is small
there in less movement in the thermometer.

Or not as the case may be.

At least that is what I gather from the study of the temperatures over
places like New York after the attack shut down all the airports in the
USA.



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