We have lots of commercial jets flying over us, most probably coming to or from Atlanta. Five of them left their contrails for us to see Sunday morning.
Contrails (condensation trails) are caused by water vapor condensing on tiny particulates in the exhaust of aircraft engines. Today we tend to think that means jet engines, but all engines produce at last some particulates. You may have seen photographs of World War II bombers flying at high altitude leaving contrails. Here’s an example taken by the Army Air Corps during WW II.
The water vapor that causes contrails can come from the water vapor produced by the engine (burning petroleum fuel produces mainly carbon dioxide and water vapor) or water vapor in the surrounding air. The water vapor may not condense into visible droplets if there are no condensation nuclei. Particulates produced in the engine combustion provide the condensation nuclei that are needed. If the air at the altitude where the aircraft is flying is not very humid, a contrail can dissipate quickly. If it is humid, the contrail can stick around for a long time, or even continue to grow and form much larger clouds.
Our skies must have been fairly humid Sunday morning because these contrails remained visible for some time.
If contrails remain visible for long enough, you may be able to see how the wind at altitude can blow in different directions at different locations by the way the line of the contrail distorts. You could also estimate the wind velocity if you were so inclined.
Bob Roper, a professor at Georgia Tech who was on my reading committee, studied what were called meteor winds. He had a radar unit that looked up at very high altitudes, near the top of the atmosphere. Meteors that routinely crash into the upper atmosphere create ionization trails that reflect radar. By measuring the apparent motion of the ionization trails as seen by the radar, the wind velocity can be estimated. If you’re really interested in meteor wind measurements, you can get one of his articles here for $31.50. Or you could probably visit your local university library and ask for help finding atmospheric science journals. I imagine that neither course will be particularly attractive, and I’m afraid the article would be pretty dry anyway.
As one of the very few scientists doing meteor wind measurements in the West, Dr. Roper sometimes got to visit the USSR, where they also did such work. Back in those days, he would be debriefed by the US authorities when he returned. One time the Russians showed him a radar that could look over the horizon and detect, let’s just say for the sake of argument, ships in the Persian Gulf. He thought that was rather odd, since he was really interested only in radars that looked pretty much straight up. He figured that the Russians would expect him to be debriefed when he returned, and that the Russians probably wanted the US to know the USSR could watch US ships from afar.
Very interesting and informative. You know there are a lot of people who call contrails chem-trails. They think it is a sinister conspiracy, “According to the chemtrail conspiracy theory, long-lasting trails left in the sky by high-flying aircraft are chemical or biological agents deliberately sprayed for sinister purposes undisclosed to the general public.” We laugh and laugh! Love the photo.
Robin — I ran across “chemtrails” before. I wonder if they thought the high-flying planes before right-wing radio and the Internet were dumping chemicals. I don’t think there’s any way to reach those people with reason. Also, Leah says “hi”.
Say “hi” to Leah for us. Hope the healing continues and all is well!
We live in an area with skies frequented by commercial and military aircraft. One afternoon last November I watched trails hang overhead for hours, increasing to close to thirty by sunset. I’d wondered why these were so persistent. Thanks for the information.
Indeed, hoping Leah is feeling much better now and will continue to do so.
Minnie — Wow! I think 30 contrails is more than I have ever seen at the same time.
Leah and I were both surprised at how long it was taking, but she is doing much better now. And so far it seems that she can expand her diet to things that were problematic before.