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If jet aircraft have always made artificial clouds, how come no one calls them cloud machines?
Being in my 50s and having had an interest in aviation since my youth, I’ve been observing jets in the sky for many years. In 1999, I first noticed a jet whose condensation trail did NOT dissipate. I figured the jet was having trouble and didn’t give it much thought. Within the next 2 years, there would be days when 90% of jet traffic left non-dissipating trails and other days when jets only produced a normal, quickly dissipating contrail. In 2003, my job took me to China for 5 years. During my years in China, I did not witness any evidence of jet aircraft leaving trails in the sky. The sky either had naturally occurring clouds or was a brilliant blue. Don’t think that China doesn’t have many jets either….during the day I could usually count 3-6 in the sky at any given time. (Being a bridge engineer allows me much time outside)

Now I’ve returned to the USA and am living in Coachella Valley (Southern CA). This once sunny area with 350+ days per year of perfect blue skies is shrouded by artificial clouds at least 50% of the time. On the clear days, there are few jets and none leave a persistent trail. On the cloudy days, there are 10X as many jet aircraft with most of those leaving trails in the sky which usually turn into high cirrus clouds or a haze.

I’m simply outraged that the locals and tourists alike are not up in arms over having our blue skies stolen away.

But remember folks, don’t believe your own eyes…..believe what big brother tells us is the truth.

Air is taken into the engine and compressed (all engines flying at high altitudes are turbo-engines) the mixed with the fuel who’s combustion leaves traces of water, that is then released in the atmosphere behind the aircraft. The actual release of the exhaust is what cools it down by the same adiabatic effect of a lesser pressure that creates clouds, and turns it into tiny ice crystal. At that stage, they are very similar to the cirrus clouds found at the top of our troposphere.

Why do some remain for a long time while others dissipate quickly? It is under the same principle that rules the clouds. Just like water evaporates in the air, even under freezing point (it is then called sublimation) clouds evaporate in the air.

Contrails are then subject to the same as clouds. What we often forget is that, in the atmosphere, the air goes as much up and down as right or left. It is only on the ground that the wind is only felt as parallel to the ground. I know that from flying a light aircraft.

A cloud that remains at the same altitude is a cloud that slowly dissipate by the thermodynamic law of entropy and evaporates.

A cloud that rises remains at the same size or increase in size by the adiabatic effect of a lesser pressure and condensation above dew point temperature.

A cloud that sinks evaporates very fast from the warming of the adiabatic effect of a greater pressure.

And that’s why contrails may sustain or disappear, according to the winds aloft. If they appear in layers of wind shear, they may even take entirely different aspects and, after a while, be difficult to differentiate with "normal" cirrus clouds.

Michel Verheughe | Dec 28, 2009

The notion that this is some kind of government plot to spray pollutants or other chemicals into the atmosphere is a ridiculous conspiracy theory that has absolutely no basis in fact. If it makes you feel better, you can go get some tin foil to line your hat. That way you won’t be subject to the thought control waves that are actually being broadcast from cell phone towers.
Paul in San Diego | Dec 28, 2009