reply to post by siouxm
siouxm,
Not sure where you are located, and I don't know how strong your binoculars were, from what you said you observed.
When I see another airplane, that is say, 2000 feet above us, in bright daylight, it looks almost completely white. Can't see windows....sometimes
can't even see the livery to determine what airline it is...this is from 2000 feet!! Less than half a mile...but I KNOW it is an airliner, because
we are on the same Airway...it is on the TCAS...it is talking to ATC...and, depending on atmospheric conditions, there may or may not be a contrail
coming from behind.
{just for perspective, when you are at an airport next time, consider that a normal runway at an International Airport is 10,000 to 12,000 feet
long}
So, from only 2000 feet, under certain lighting conditions, an airplane will look pure white...and you are looking, thru binoculars, at an airplane
that is probably 31,000 feet above you, depending on your sea level from viewpoint.
The term 'contrail' is a compound word that comes from 'condensation' and 'trailing'...so, it is actually a 'trailing condensation cloud'.
Condensation occurs when there is a sufficient temperature, or pressure, or combination of both, change so that the 'invisible' moisture that is
contained in the air must 'condense' out, sinse it is a) too cold or, b)too dense to hold the moisture anymore. This is called 'saturation'.
Do the insides of the windows of your auto ever 'fog' up, in certain conditions? Do you understand why that happens? Do you notice that when you
use the 'defog' function in your auto, your Airconditioner Compressor kicks on? Know why? Because the A/C coils will change the specific gravity
of the moisture in the air, in the case of your auto, the interior air...the excess moisture will drip off the coils of the A/C system...you will see
this sometimes when you park your car, the move it after only a few minutes....
An airliner, moving through the air, will cause a disturbance...as a result of the lift generated by the wing, there will be a compression effect to a
certain part of the airmass. Any latent moisture in the affected airmass will be 'squeezed' out, and appear as 'contrails'. What's more, the
hot air expelled from the engines will interact, will increase the temp and pressure temporarily, but after several feet in trail of the jet, the air
will cool, and the moisture will condense out...
Sometimes an airliner will travel through a mass of air, and produce NO contrail....becaue the airmass happens to be dry, or devoid enough of
moisture, hence no 'contrail'.
Occasionally, you will see 'contrails' that seem to start, and stop...like Morse Code...simple reason, not all Upper Level Winds in our atmosphere
are 'layered', or 'smooth'. Sometimes, especially after interacting with surface terrain, such as mountains, or even hills, they will undulate.
Invisible to the naked eye, but well noticed by 'contrails'. BTW, that's usually why you feel 'turbulence' when onboard a jet. Layers of
'shear' in the atmosphere (not to be confused with WindShear, which is a term we use when near the ground, for take-off and landing....usually
associated with nearby thunderstorms, but not always...).
