Origin of 3 contrail pseudoconditions?

cmnit

Member
Hi all, as most (or all) of you I'm sick and tired of reading and hearing about the chemtrailist mantra regarding the infamous 3 pseudoconditions for contrail formation:
1. height of flight > 8000 m
2. temperature < -40 C
3. relative humidity > 70%

It is amazing how this meme reproduces itself without mutations ... but now I am curious about the originator of this "trick". Maybe you wrote about this before somewhere in the forum or in the contrail science site? Thanks anyway!
 

Rico

Senior Member.
These are just common figures you find in scientific literature pertaining to atmospheric science. Just at a quick glance, 8000 m is often cited as the height where you begin to see cirrus clouds. I know at least one textbook that calls out -40 C as the temperature where you start seeing persistent contrails. RH 70% is also mentioned from a number of sources. Wikipedia cites 8,000m, -36.5 degrees, and RH 60%, as when contrails "usually forms". (Source: http://en.wikipedia.org/wiki/Contrail)

Generally, you will tend to see contrails with these conditions, so they are not necessarily "pseudoconditions." I think the problem that a lot of chemtrail believers have is that they tend to assert that thou must have all these conditions for a contrail to form, which is blatantly false if only they understood why height, temperature, and RH are significant. In short, they take these numbers at face value, and often out of context.

For example, while a lot of contrails do form at heights greater than 8,000 meters (~26,000 feet), it may totally escape some people that they can form at lower altitudes if the temperature was colder (heck, here in Canada, it's not unusual seeing -40 at 5,000 feet on a cold winter day, or even at the surface). I am pretty sure most people don't even realize that the colder the temperature gets, the less moisture the air can carry before that moisture is condensed, and thus visible to the naked eye. There is also the factor that temperatures tend to decrease as you go up in altitude (exception is an inversion), which is a fact that often gets left behind when advocating chemtrails.
 
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cmnit

Member
Thanks Rico for the detailed explanation. Still, I have this feeling that someone in particular started to use the argument without context as you describe in the chemtrail camp, so that all others followed easily. Just curious.
 

skephu

Senior Member.
In addition, aerodynamic contrails form at lower altitudes and warmer temperatures, and are often hard to distinguish from exhaust contrails.
 

Efftup

Senior Member.
Thanks Rico for the detailed explanation. Still, I have this feeling that someone in particular started to use the argument without context as you describe in the chemtrail camp, so that all others followed easily. Just curious.
Similar to the contrails don't persist, ergo they must be chemtrails argument. It gets parotted around as fact so much that nobody ever bothers to check up where that idea came from.
 
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Mick West

Administrator
Staff member
The figures are reasonably rules of thumb as to when contrails are likely to form, however when the theorists use them to "prove" that a contrail should not have formed they are almost always referring to contrails that DO fall within those values.

They do one or more of:
  1. Underestimate the height, thinking if they can see the plane it must be very low, or if it is close to the horizon (even if it's too small to see) then it must be close to the ground.
  2. Overestimate the temperature, thinking "I live in Las Vegas, it's summer, so obviously it's not -40!!"
  3. Underestimate the humidity, either for the reason above ("I live in the desert, where it is dry") or using radiosonde soundings which generally don't register humidity with any accuracy below -40°F/C, and only give spot measurements anyway.
That covers the majority of cases, but I have seen also people point out contrails in the UK at around 18,000 feet in the winter - which is just a misunderstanding of the function of altitude.
 

Donnn

New Member
I was also involved in discussions about similar parameters.

Is there any data on the following questions?
-How often do persistent contrails (longer than 20 min) form? Some people say they form rarely, only under very special circumstances, other say are a regular phenomena. So when looking at the whole year, what is the average amount of days that would be suitable for the forming of persistent contrails, say in a central European climate. Any way to find out?

-How often do contrails become a cirrus cloud. Is this a "rare" event, as claimed by some? Or a "frequent" event.
I know these words need a better definition, but I am only re-using the words I read from meteorologists, where some claim it is a "rare" event. Are there any numbers, like percentage?
 

Mick West

Administrator
Staff member
Is there any data on the following questions?
-How often do persistent contrails (longer than 20 min) form? Some people say they form rarely, only under very special circumstances, other say are a regular phenomena. So when looking at the whole year, what is the average amount of days that would be suitable for the forming of persistent contrails, say in a central European climate. Any way to find out?
It's a complicated question, with complicated answers. See:
http://www-pm.larc.nasa.gov/sass/pub/conference/JP1.15.duda.arams.02.pdf

0.197 and 0.269 are the frequency of persistent contrail conditions, so about one out of ever 4 or 5 days, on average. But looking at the chart, some areas get a lot more than others, and it varies a lot with the weather.
 

Trailblazer

Moderator
Staff member
I was also involved in discussions about similar parameters.

Is there any data on the following questions?
-How often do persistent contrails (longer than 20 min) form? Some people say they form rarely, only under very special circumstances, other say are a regular phenomena. So when looking at the whole year, what is the average amount of days that would be suitable for the forming of persistent contrails, say in a central European climate. Any way to find out?

-How often do contrails become a cirrus cloud. Is this a "rare" event, as claimed by some? Or a "frequent" event.
I know these words need a better definition, but I am only re-using the words I read from meteorologists, where some claim it is a "rare" event. Are there any numbers, like percentage?
According to a study by Reading University, about 7% of the total flight distance by airliners is in conditions were persistent contrails will form:

http://www.reading.ac.uk/news-and-events/releases/PR586136.aspx

Note that that percentage includes the take-off and landing phases where the aircraft are not at cruising altitude, so the actual percentage for aircraft at cruising height will presumably be slightly higher than this.

This paper specifically studies the frequency of "cold ISSRs" (ice super-saturated regions, where contrails will persist) over the north Atlantic: http://onlinelibrary.wiley.com/doi/10.1029/2012GL051909/full

upload_2015-5-19_11-54-8.png

upload_2015-5-19_11-55-23.png
upload_2015-5-19_11-59-2.png

In altitude terms, 300hPa is about 30,000 feet, and 200hPa is about 38,700 feet, which are close to the lower and upper ranges of aircraft cruising altitude.
 
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