Bernard Burton wrote:
Jack,
It seems to me that aircraft exhaust trails must go through a liquid
phase before freezing. As the exhaust plume exits the engine, it is
at a temperature of several hundred degrees C. Even though mixing
with the environmental air is very rapid, the temperature at which
condensation occurs, at normal aircraft operating levels up to the
tropopause, will always be above -40C, and the condensation product
will always be water. Depending on the environmental conditions, the
rapid mixing in the plume will often result in equally rapid freezing
of the droplets as their temperature falls to -40C and below, at
which point virtually no liquid droplets would exist. For a more
thorough treatment see Clouds of the World by Richard Scorer, ch11.
So, to answer your query, the term condensation trail is indeed
correct.

Satellite images at:
www.btinternet.com/~wokingham.weather/wwp.html
"Jack Harrison" wrote in message
...
A couple of definitions from eg
http://nsidc.org/arcticmet/glossary/condensation.html
(other websites confirm the definitions)

CONDENSATION
The physical process by which a vapor becomes a liquid or solid; the
opposite to evaporation.
In meteorological usage, this term is applied only to transformation
from vapor to liquid; any process in which a solid forms directly
from its vapor is termed SUBLIMATION, as is the REVERSE process.
(my capitals)

So are we correct in calling them condensation trails?
(As a four to five year old during WW2, we used to call them vapour
trails - seemingly no less accurate).
Condensation nuclei (from the engine exhausts) are of course
necessary for the water vapour to be able to sublimate into ice
cloud, so would it be totally wrong to call them "smoke induced"
trails?

Jack

I'd go with that. It's still a condensate, wether it forms around particles
or not.

Pharm.