Jet Trails

The appearance of trails behind jets is caused by one of two things:

"Negative Pressure Zone": Water vapor from the air that condenses in the negative-pressure zone of wing tips or flaps; or,
"Ice Crystals": Condensed ice in the upper atmosphere forming around moisture from jet exhaust.

"Negative Pressure Zone" Trails

"Negative Pressure Zone" trails only occur when humidity is very high. They only last as long as a negative pressure zone persists. Below is a photo of a typical NPZ trail.

In this picture, you will notice that the trail dissipates almost completely just a few feet behind the wing. This occurs because the moisture in the trail is reabsorbed back into the air as quickly as the air pressure increases towards normal. The trail in the picture is not visible from the ground.

I've seen this principle demonstrated when a vacuum is applied in a glass jar in a high-school science class. Sometimes, you will see condensation form in the jar as the vacuum increases, but when the vacuum is released, all of the condensation dissipates immediately.

"Ice Crystals"

Under certain, very specific conditions, jets flying at high altitudes in very cold air cause water vapor to condense. This vapor then freezes back into small ice crystals. These tiny ice crystals are immediately exposed to the direct sun in the upper atmosphere and melt, dissipating usually within seconds. These trails are so thin and short-lived that they have rarely been seen at any altitude.

Furthermore, because this phenomenon is extremely rare and because it only occurs in the upper atmosphere, these types of trails are simply not visible from the ground.

Historical Rarity of Contrails

Both of the trails described above are called "contrails".

Contrails are extremely rare, but on the rare occasion that one does form in the upper atmosphere, it dissipates quickly and cannot be see from the ground. It's simply too high and too small and thin.

I have been a sky-watcher nearly all of my life. I grew up near some of the most heavily-traveled airspace in the world. I also lived on a military base. I have traveled across the United States visiting over 20 states multiple times.

Throughout the past 30 years, all across this country, I have watched thousands upon thousands of jets fly across the sky. Most of them were commercial jets, others were military, but they all had one thing in common:

They never left a trail.

Yes, after 30 years of sky-watching, I have never seen a single jet leave a trail... until now. In fact now I was seeing many more jets in the sky, and most of the had trails.

« Previous Page | Next Page »